Dissertations / Theses on the topic 'Ocean acidification'

Ocean acidification has been called the ‘evil twin’ of climate change and has become acknowledged as a serious risk to the marine environment. This thesis aims to explore public perceptions of ocean acidification as there is limited work on how people understand this emerging risk. It is important to engage the public because ocean acidification will contribute to how carbon emissions are addressed. The mental models approach was used to compare and examine public and expert perceptions of ocean acidification to help inform future risk communications. Many of the findings were similar to those of climate change; for example, it was not seen as a personal risk but something which would impact on the environment. Results showed that ocean acidification was unfamiliar to the public with low levels of knowledge and awareness found. People could identify possible impacts of ocean acidification but they were unsure about the main cause, stating that pollution from chemicals and industrial waste was one of the main causes. Risk perceptions of ocean acidification were influenced by factors other than knowledge about the risk such as affect, place attachment and environmental identity. A key finding of this thesis was that people were concerned about ocean acidification despite this being an unfamiliar risk issue, perceiving it as a highly negative risk. This exploratory thesis will help develop more effective risk communications around ocean acidification with these findings in mind. Future work should test ocean acidification frames; whether or not it should be framed as part of climate change. The mental models approach allowed initial understandings of this unfamiliar risk to be explored using mixed methods and helped examine how ocean acidification was conceptualised through social representations theory. Public response to ocean acidification may mean that there would be greater support for policies aimed at reducing carbon emissions.

Ocean acidification (OA) as a result of anthropogenic CO2 accumulation has major implications for the calcification of marine organisms. Assessing the calcification response of coccolithophores and planktic foraminifera to OA in particular is paramount as together they produce the majority of pelagic carbonate burial and thus impact biogeochemical cycling and oceanic CO2 uptake. In this thesis, two sediment cores from Eirik Drift and the Norwegian Sea are used to reconstruct the natural calcification response of marine plankton since the Last Glacial Maximum and compare these changes to recent anthropogenic influences over the last 200 years. Reconstructions of the bottom water dynamics and thus sedimentation at Eirik Drift infers the suitability of the core for palaeo-analysis of plankton calcification. The calcification response of three foraminiferal species and two morphotypes of the dominant polar species Neogloboquadrina pachyderma are significantly correlated throughout the Holocene suggesting similar calcification mechanisms between and within species. Although the drivers of calcification appear to vary temporally and geographically, down-core planktic foraminiferal Mg/Ca and faunal assemblage counts point towards the importance of sea surface temperature and optimal growth conditions on the calcification of N pachyderma. Unlike Globigerina bulloides, N pachyderma shows little sensitivity to CO2 changes across the last deglaciation Since the beginning of industrialisation, foraminiferal calcification fluctuates within the natural long-term trends observed over the last 22 kyrs inferring minimal anthropogenic impacts on foraminiferal calcification. Interspecies-specific responses are evident, as the test weight of G. bulloides increases since the early 1900s in response to a warming North Altantic Current, whilst Neogloboquadrina incompta shows little change over the last 200 years. Furthermore, an increase in the degree of calcification of the abundant coccolithophore Emiliania huxleyi occurs in response to accelerated 20th century climate change pointing towards increased carbonate burial in the sub-polar North Atlantic under future global change.

Global industrialisation has led to the anthropogenic raising of global CO2 concentration from 280 pp to over 380 ppm in the last 200 years causing oceanic pH to drop by 0.1 unit as a result of a processes called ocean acidification. It is expected to further drop by between 0.3 and 0.4 units over the next 100 years. Quantifying the impact of such a pH shift has, to date, largely relied on laboratory studies of model organisms or simple assemblages in mesocosms. Conversely, this work undertook a series of field experiments to examine the effect of predicted pH environmental conditions on a robust marina fouling assemblage and microorganisms through the manipulation of local CO2 concentration. CO2 was delivered and controlled above replicated settlement panels that were freely accessible to normal propagule supply. Over 5 months, recruitment and development of macroorganisms and diversity of microorganisms in biofilms was shown to be largely unaffected by low pH. Results of this investigation were contrasted against microbial diversity in biofilms from a low pH volcanic vent site. Molecular analysis of biofilms failed to detect an influence of pH on diversity. The development of an alternative method of CO2 delivery using silicone membranes is described, which proved to have both antifouling and ocean acidification experimental applications. In conclusion, the marine organisms examined in this study showed little response to pH change of the order that is expected with the progression of ocean acidification. Significant methodological advances to in situ pH experimentation have been made, however, which should assist further investigations.

The oceanic uptake of anthropogenic CO2 emissions is leading to an alteration of seawater carbonate chemistry, manifested as increasing [H+], falling [CO32-] and a drop in seawater pH. Over the coming centuries this process, termed “ocean acidification”, is expected to negatively impact marine biota, with implications for marine biological and biogeochemical processes. In this thesis, the impact that such changes may have on the net production of a range of climatically- and atmospherically-important marine biogenic trace gases, including halocarbons and dimethyl sulphide (DMS), is assessed through a mesocosm phytoplankton bloom CO2 perturbation experiment, two laboratory CO2 incubation experiments on natural seawater samples, and at a volcanically-acidified shallow marine fieldsite in Italy. Large and significant reductions in DMS and DMSP concentrations under future high CO2 conditions were observed during the mesocosm experiment (mean decreases of 57 percent and 24 percent, respectively), a finding in strong support of a previous study (Avgoustidi 2007). Furthermore, concentrations of iodocarbons showed large decreases, with mean decreases under high CO2 ranging from 59 to 93 percent. Results for the laboratory incubation experiments also showed a reduction in iodocarbon concentrations (when normalised to chlorophyll a) under high CO2. These changes may be the result of shifts in plankton community composition in response to the high CO2 conditions, and/or impacts on dissolved organic matter and the bacterial communities involved in the formation of these compounds. The response of bromocarbons was less clear cut during the experimental studies. Following investigations at a naturally-acidified fieldsite in Italy, it was concluded that this site was a poor natural analogue to the impact of future ocean acidification on marine trace gas production. Taking the results of the mesocosm and laboratory incubations into consideration, a combined decrease in both DMS and iodocarbons in response to ocean acidification may have considerable impacts on future atmospheric chemistry and global climate.

The ecophysiology of calcified macroalgal species of the genera Corallina (C. officinalis and C. caespitosa) and Ellisolandia (E. elongata) (Corallinales, Rhodophyta) was examined in intertidal rock pools of the NE Atlantic, to facilitate predictions of ocean-acidification and warming impacts on these ecosystem engineers. An initial phylogenetic study highlighted significant cryptic diversity within the genus Corallina, and demonstrated that C. officinalis is restricted predominantly to the North Atlantic, while the recently established C. caespitosa shows a cosmopolitan distribution. Three subsequent studies were performed across the NE Atlantic (Iceland to northern Spain) to examine (i) the production, respiration, calcification and growth of Corallina in relation to irradiance, water temperature, and carbonate chemistry; (ii) the photoacclimation and photoregulation strategies of Corallina and Ellisolandia; and (iii) the recent-past (1850 – 2010) and present-day skeletal mineralogy (Mg/Ca ratios) of Corallina and Ellisolandia and its relationship to sea surface temperature. Data demonstrated that species currently experience significant seasonal and tidal fluctuations in abiotic conditions that may be important when considering future responses to ocean-acidification and climate-change. Seasonality in production, calcification and growth were demonstrated, with decreasing growth observed with increasing latitude. Photoacclimation to allow maximal light utilisation during winter periods, and photoregulation via nonphotochemical quenching were highlighted as important in allowing Corallina and Ellisolandia to maintain maximal productivity while controlling for photo-stress. Seasonal cycles in skeletal Mg incorporation were demonstrated with strong relation to sea surface temperature, though no significant change in skeletal mineralogy was evident since pre-industrial times. Taken together, data indicated that Corallina and Ellisolandia have the potential to survive under future ocean-acidification and warming conditions, though loss of species at high latitudes and shifts in the relative abundances of species across the region is likely to be evident, with overall range contraction predicted for C. officinalis due to both warming and ocean-acidification impacts.

Elevated atmospheric concentrations of carbon dioxide (CO₂), partly driven by anthropogenic activity, are decreasing the pH of the oceans. This thesis aimed to assess the biological response of foraminifera to ocean acidification. Foraminifera are single-celled organisms that form the dominant component of many marine communities. A series of laboratory experiments were carried out on benthic intertidal foraminifera from the Eden and Ythan estuaries, NE Scotland, to assess the impacts of ocean acidification. The responses of two dominant intertidal species of foraminifera (Haynesina germanica and Elphidium williamsoni) to ocean acidification were initially investigated in a short-term (6 week) experiment. Multiple species and multiple stressors (seasonal temperature regime and elevated CO₂) were then incorporated in a long-term (18 month) mesocosm study to investigate the physiological consequences (e.g. survival, growth) of ocean acidification. Survival of both Haynesina germanica and Elphidium williamsoni was significantly reduced under low pH conditions. Live specimens of both these calcareous species were however recorded at low pH, in reduced numbers. Following long-term exposure to ocean acidification, foraminiferal populations were still dominated by calcareous forms. Agglutinated foraminifera were recorded throughout the long-term incubations but their numbers were not high enough in the initial sediment collections to allow them to contribute significantly to the populations. Overall, survival of all foraminifera was greatly reduced in elevated CO₂ treatments. Temperature effects were observed on foraminiferal survival and diversity with the largest CO₂ effects recorded under the seasonally varying temperature regime. Foraminiferal test damage for all live species was also highest under elevated CO₂ conditions. Test dissolution was particularly evident in Haynesina germanica with important morphological features, such as functional ornamentation, becoming reduced or completely absent under elevated CO₂ conditions. A reduction in functionally important ornamentation could lead to a reduction in feeding efficiency with consequent impacts on this organism's survival and fitness. In addition, changes in the relative abundance and activities of these important species could affect biological interactions (e.g. food web function) and habitat quality.

2013/2014
Since the beginning of Industrial Revolution a massive amount of atmospheric carbon dioxide, produced by human activity, has been absorbed by the World’s Oceans. This process has led to an acidification of marine waters on a global scale and is one of the most serious threats facing marine ecosystems in this century. The negative impacts of ocean acidification could be much more relevant in coastal ecosystems, where marine life is concentrated and biogeochemical processes are more active. However, future projections of pH reduction in these areas are difficult to estimate because result from multiple physical and biological drivers, including watershed weathering, river-born nutrient inputs, and changes in ecosystem structure and metabolism. In order to assess the sensibility of the Gulf of Trieste to the ocean acidification, high quality determination of the marine carbonate system (pHT, total alkalinity, dissolved inorganic carbon-DIC, buffer capacity) and other related biogeochemical parameters were carried out along a transect from the Isonzo River mouth to the centre of the gulf and at the coastal Long Term Ecological Research station C1. At the same time the biological influence of organic matter production and decomposition on the marine CO2 system was estimated using 14C primary production and heterotrophic prokaryote production (by 3H-leucine incorporation). The two years long measurements revealed a complex dynamic of the marine carbonate system, due to the combined effects of local freshwater inputs, biological processes, and air-sea CO2 exchange. However, it was possible to estimate the influence of the different drivers on a seasonal time scale. In winter the very low seawater temperature (minima = 2.88 °C) and strong Bora events determined a marked dissolution of atmospheric CO2 and elevated DIC concentration. During warm seasons the DIC concentration gradually decreased in the surface layer, due to biological drawdown (primary production) and thermodynamic equilibria (CO2 degassing), whereas under the pycnocline the respiration and remineralisation of organic matter prevailed, causing a temporary acidification of bottom waters. The winter seawater invasion of atmospheric CO2 was balanced by high riverine AT input (maxima ∼ 2933 µmol kg-1), derived mainly from chemical weathering of carbonate rocks of the surrounding karstic area, which increased the buffer capacity of this system and probably could mitigate the effect of ocean acidification. The marine carbonate system was also analysed in the Middle and Southern Adriatic Sea, in order to estimate the concentration of anthropogenic carbon dioxide currently present in this area. The results suggested that the entire water column was contaminated by a large amount of anthropogenic CO2 and very high concentration was detected near the bottom, in correspondence of the North Adriatic Dense Waters. This finding supported the hypothesis that during dense water formation events the very low seawater temperature can favour the physical dissolution of atmospheric carbon dioxide, and also revealed the active role of the North Adriatic Sea in sequestering and storing anthropogenic CO2 into the deep layers of Mediterranean Sea.
Dall’inizio della Rivoluzione Industriale ad oggi, una grande quantità di anidride carbonica antropogenica presente in atmosfera è stata assorbita dagli Oceani di tutto il mondo. Questo processo ha portato all’acidificazione del mare su scala globale e rappresenta una delle più gravi minacce per gli ecosistemi marini in questo secolo. L’impatto negativo di tale fenomeno, noto come ocean acidification, potrebbe essere maggiore soprattutto negli ecosistemi costieri, poiché è qui che si concentrano gli organismi marini ed è qui che i cicli biogeochimici risultano più attivi. Tuttavia è difficile stimare il futuro abbassamento del pH in queste aree a causa della loro complessità e della moltitudine dei processi fisici, chimici e biologici coinvolti (cambiamenti dello stato trofico e del metabolismo dell’ecosistema, input fluviale di nutrienti, materia organica e prodotti di dissoluzione delle rocce, ecc.). Allo scopo di valutare la vulnerabilità del Golfo di Trieste rispetto al processo di ocean acidification, per due anni sono state eseguite misure di elevata precisione del sistema carbonatico marino (pHT, alcalinità totale, carbonio inorganico disciolto-DIC, capacità tamponante) e di altri parametri biogeochimici correlati lungo un transetto che congiunge la foce del fiume Isonzo al centro del Golfo e nella stazione C1 sito LTER (Long Time Ecological Research C1). Inoltre, per valutare in maniera più approfondita l’influenza dei processi biologici sulla variabilità del sistema carbonatico, è stata stimata la produzione primaria, attraverso il metodo dell’incorporazione di 14C, e la produzione procariotica eterotrofa, attraverso l’incorporazione di 3H-leucina. I risultati hanno evidenziato una complessa dinamica del sistema carbonatico dovuta all’effetto e all’interazione degli apporti fluviali, dei processi biologici e dello scambio di CO2 tra atmosfera e mare. Su scala stagionale, tuttavia, è stata stimata l’influenza e il contributo dei diversi processi. In inverno, la bassa temperatura dell’acqua, che in un caso estremo ha raggiunto i 2.88 °C, e i forti venti di Bora hanno favorito la dissoluzione della CO2 atmosferica, determinando un incremento della concentrazione di DIC. Durante la primavera e l’estate i livelli di DIC sono diminuiti gradualmente negli strati superficiali, grazie all’effetto combinato della produzione primaria e alla perdita di CO2 verso l’atmosfera per degassamento. Nel periodo tardo estivo-autunnale, invece, al di sotto del picnoclino i processi di respirazione e remineralizzazione della materia organica sono risultati predominanti determinando, a causa dell’elevata concentrazione di CO2 prodotta, una temporanea acidificazione delle acque di fondo. Il forte assorbimento di CO2 atmosferica stimato durante l’inverno era, però, controbilanciato dall’apporto fluviale di alcalinità totale, derivante dal processo di dissoluzione delle rocce calcaree presenti nell’area carsica. Tale fenomeno ha determinato un aumento della capacità tamponante del sistema, mitigando probabilmente il processo di ocean acidification in quest’area. Parallelamente alle analisi nel Golfo di Trieste, il sistema carbonatico marino è stato analizzato anche nel Medio e Sud Adriatico, con lo scopo di stimare la concentrazione di anidride carbonica antropogenica attualmente presente in questi sottobacini. I risultati hanno dimostrato come tutta la colonna d’acqua avesse assorbito una grande quantità di CO2 antropica. In particolare elevate concentrazioni sono state individuate sul fondo, in corrispondenza delle acque dense di origine nord adriatica. Tali risultati hanno confermato l’ipotesi secondo la quale in inverno, durante il processo di formazione di acque dense nel Nord Adriatico, le basse temperature raggiunte dalle acque possono favorire la dissoluzione fisica della CO2 atmosferica. Hanno dimostrato, inoltre, l’importante ruolo svolto da tutto il bacino nord adriatico nel sequestrare e trasportare la CO2 antropica nelle profondità del mare, estendendo il processo di ocean acidification anche ad aree meno contaminate.
XXVII Ciclo
1982

Increasing anthropogenic atmospheric CO₂ is altering the chemistry of surface seawater worldwide, resulting in ocean acidification. Experiments have begun to demonstrate the detrimental consequences that a CO₂-mediated decline in ocean pH can have on the growth and survival of calcifying organisms. However, significant knowledge gaps exist both in our understanding of the mechanisms driving the observed reductions in shell growth rates of organisms exposed to increases in CO₂, and in our ability to predict how these individual-level effects could scale-up to the population or community-level. Using laboratory exposure experiments in which levels of dissolved CO₂ were carefully manipulated, we tested the effects of climatically relevant increases in CO₂ levels on a) both shell deposition rate and shell dissolution rate in the intertidal snail, Nucella lamellosa, and b) the growth and feeding behaviour of juvenile red sea urchins, Strongylocentrotus franciscanus. Based on the results of the former study, we found that shell weight gain per day in live snails decreased linearly with increasing CO₂ level while shell weight loss per day in empty shells more than doubled over this same range. These results suggest that for some species, elevated CO₂ levels may have a much greater effect on shell dissolution than shell deposition. In the latter study, although we found no effect of a doubling of current CO₂ concentration on the individual feeding rates or absorption efficiency of juvenile urchins, there was a significant reduction in relative growth rates at the higher CO₂ concentration after 4 months of exposure. Applying the urchin growth data to a simple demographic matrix model, and incorporating empirical relationships between urchin test diameter, biomass and kelp consumption rates to the model outputs, we estimated that if current CO₂ levels were to double by the end of the century, it would take significantly longer for urchins to reach reproductive and harvestable sizes, and their per capita kelp grazing rates would be significantly reduced. These simple model applications illustrate how CO₂-mediated reductions in individual growth rates could indirectly impact important population-level attributes such as time to first reproduction, and could have community- or ecosystem-level effects by moderating the importance of top-down biological control.

Since industrialisation global CO2 emissions have increased, and as a consequence oceanic pH is predicted to drop by 0.3-0.4 units before the end of the century - a process coined ‘ocean acidification’ (OA). There is significant interest therefore in how pH changes will affect the oceans’ biota and integral processes. This thesis investigates microbial community organisation and functioning in response to predicted end of century CO2 concentrations using an elevated CO2 (~750ppm), large volume (11,000 L) contained seawater mesocosm. This thesis utilises RNA stable isotope probing (SIP) technologies, in conjunction with quantitative reverse transcriptase PCR (RT-qPCR), to investigate the response of microbial communities to elevated CO2. This thesis finds little evidence of changes occurring in bacterial abundance or community composition with elevated CO2, under both phytoplankton pre-bloom/bloom and post-bloom conditions. It is proposed that they represent a community resistant to the changes imposed. In contrast, significant differences were observed between treatments for a number of key eukaryote community members. These findings were investigated in the context of functional change, using the uptake of two key substrates (bicarbonate and glucose) as analogues for photosynthesis and respiration respectively. Unlike community abundance, distinct changes in carbon assimilation were detected in dominant members of the picoplankton. In conclusion the data presented suggest that although current microbial communities hold the capacity to respond to elevated CO2, future responses will likely be taxa specific and controlled by wider community dynamics.

Ocean acidification may cause biodiversity loss, alter ecosystems and impact food security, yet uncertainty over ecological responses to ocean acidification remains considerable. Most work on the impact of ocean acidification on foraminifera has been short-term laboratory experiments on single species. To expand this, benthic foraminiferal assemblages were examined across shallow water CO2 gradients in the Gulf of California, off the islands of Ischia and Vulcano in Italy and off Papua New Guinea. Living assemblages from the Gulf of California did not appear to show a response across a pH range of 7.55 – 7.88, although the species assemblage was impoverished in all locations and the dead assemblage was less diverse at the lowest pH sites where there was evidence of post mortem dissolution. At Vulcano, the small macroalga, Padina pavonica, did not protect calcareous foraminifera from the adverse effects of ocean acidification. Calcareous taxa disappeared from the assemblage and were replaced by agglutinated foraminifera as mean pH reduced from 8.19 to 7.71. Settlement of benthic foraminifera onto artificial collectors off Vulcano was adversely affected in the acidified water, with few species as pCO2 increased and evidence of post-mortem dissolution. The foraminiferal tests, collected off Papua New Guinea, had lower δ11B as mean pH decreased from 7.99 – 7.82 for small (250 – 500 µm) Amphistegina lessonii, but not for A. lessonii or Calcarina spengleri >500 µm. In the larger foraminifera, photosynthetic activity by symbionts may begin to dominate the boron isotopic signature. Overall, the responses of foraminiferal assemblages to ocean acidification are complex, but there was an overall reduction in species diversity in infaunal, epifaunal and epiphytic assemblages as pCO2 increased. This raises serious concerns for the survival of shallow water calcareous benthic foraminifera as the oceans continue to acidify, with implications for benthic ecosystems and inorganic carbon cycling.

Since the industrial revolution, the ocean has absorbed around one third of the anthropogenic CO2, which induced a profound alteration of the carbonate system commonly known as ocean acidification. Since the preindustrial times, the average ocean surface water pH has fallen by 0.1 units, from approximately 8.2 to 8.1 and a further decrease of 0.4 pH units is expected for the end of the century. Despite their microscopic size, marine diatoms are bio-geo-chemically a very important group, responsible for the export of massive amount of carbon to deep waters and sediments. The knowledge of the potential effects of ocean acidification on the phytoplankton growth and on biological pump is still at its infancy. This study wants to investigate the effect of ocean acidification on the growth of the diatom Skeletonema marinoi and on its aggregation, using a mechanistic approach. The experiment consisted of two treatments (Present and Future) representing different pCO2 conditions and two sequential experimental phases. During the cell growth phase a culture of S. marinoi was inoculated into transparent bags and the effect of ocean acidification was studied on various growth parameters, including DOC and TEP production. The aggregation phase consisted in the incubation of the cultures into rolling tanks where the sinking of particles through the water column was simulated and aggregation promoted. Since few studies investigated the effect of pH on the growth of S. marinoi and none used pH ranges that are compatible with the OA scenarios, there were no baselines. I have shown here, that OA does not affect the cell growth of S. marinoi, suggesting that the physiology of this species is robust in respect to the changes in the carbonate chemistry expected for the end of the century. Furthermore, according to my results, OA does not affect the aggregation of S. marinoi in a consistent manner, suggesting that this process has a high natural variability but is not influenced by OA in a predictable way. The effect of OA was tested over a variety of factors including the number of aggregates produced, their size and sinking velocity, the algal, bacterial and TEP content. Many of these variables showed significant treatment effects but none of these were consistent between the two experiments.

Empirical algorithms are developed using high-quality GO-SHIP hydrographic measurements of commonly measured parameters (temperature, salinity, pressure, nitrate, and oxygen) that estimate pH in the Pacific sector of the Southern Ocean. The coefficients of determination, R-2, are 0.98 for pH from nitrate (pH(N)) and 0.97 for pH from oxygen (pH(Ox)) with RMS errors of 0.010 and 0.008, respectively. These algorithms are applied to Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) biogeochemical profiling floats, which include novel sensors (pH, nitrate, oxygen, fluorescence, and backscatter). These algorithms are used to estimate pH on floats with no pH sensors and to validate and adjust pH sensor data from floats with pH sensors. The adjusted float data provide, for the first time, seasonal cycles in surface pH on weekly resolution that range from 0.05 to 0.08 on weekly resolution for the Pacific sector of the Southern Ocean.

Esta tesis analiza los efectos socio-económicos de la acidificación oceánica y del calentamiento del Mediterráneo. Estas presiones ambientales vienen provocadas por el incremento de las emisiones de CO2 desde la Revolución Industrial. La combinación de estas presiones puede tener consecuencias negativas sobre hábitats y especies (p.e., coralígeno, bivalvos y gorgonias) junto con pérdidas económicas para la acuicultura y el turismo. Esta tesis ha investigado dichas pérdidas, desarrollando las siguientes actividades: 1) desarrollo del marco conceptual para el estudio del impacto socio-económico de la acidificación en el Mediterráneo; 2) diagnóstico de la vulnerabilidad potencial de la acuicultura de moluscos del Mediterráneo respecto a varias presiones ambientales, según las percepciones del sector; 3) valoración del impacto de la acidificación y calentamiento del mar sobre los beneficios recreativos del buceo en zonas marinas protegidas (ZMP) del Mediterráneo compuestas por el coralígeno y gorgonias; y 4) transferencia de valores ambientales, en concreto, costes en términos de bienestar y pérdidas de ingresos turísticos a causa de estas presiones, utilizando un modelo ecológico para varias ZMP de la región Euro-Mediterránea. Las principales conclusiones son cinco: primero, la acidificación y el calentamiento del mar son perceptibles en el Mediterráneo y pueden verse acentuados durante el presente siglo. Hábitats coralígenos, arrecifes de vermétidos y praderas de Posidonia, y otras especies (p.e., especies planctónicas, bivalvos, gorgonias) son vulnerables respecto a ambas presiones. Los servicios ecosistémicos potencialmente afectados incluyen la provisión de alimentos, el soporte de actividades recreativas, la protección costera y la captura de carbono. Los sectores amenazados incluyen la pesca, la acuicultura o el turismo. Segundo, los cuestionarios a productores y ZMP indican que la acidificación es un fenómeno poco conocido y que existe una alta incertidumbre sobre sus consecuencias futuras. Muchos de los encuestados la consideran como una amenaza menor en comparación con olas de calor, el incremento gradual de la temperatura del mar o los brotes de algas tóxicas. Las olas de calor constituyen una importante preocupación para el sector acuícola, debido a experiencias recientes. Tercero, la acidificación y el calentamiento del mar pueden perjudicar zonas de buceo del Mediterráneo con hábitat coralígeno. Los resultados de un experimento basado en la elección de alternativas, realizado en la ZMP de las Islas Medes (España), indican posibles pérdidas en términos de bienestar de los buceadores para los escenarios de reducción de 50% y 100% de las gorgonias (p.e., coral rojo, gorgonia roja), de -17€ y -60€/inmersión, respectivamente. Además, el análisis de las probabilidades de selección (o rechazo) de experiencias de buceo según escenarios climáticos indica la posible pérdida de ingresos turísticos, hecho que puede perjudicar las economías locales y la financiación de las ZMP. Cuarto, estos resultados fueron extrapolados para otras ZMP similares del espacio Euro-Mediterráneo. El análisis mediante transferencia de valores ambientales se llevó a cabo junto al uso de costes en términos de bienestar y pérdidas de ingresos turísticos a partir de los resultados de un modelo ecológico para el hábitat coralígeno. Dicho modelo indica que las condiciones para la presencia del hábitat coralígeno serán probablemente menos favorables en el futuro. Las estimaciones de los costes en términos de bienestar y pérdidas de ingresos asociados alcanzarían máximos de 36,6 y 20,780 millones de euros, respectivamente. Por último, el análisis de los efectos socio-económicos de la acidificación y calentamiento del mar se enfrenta a varios desafíos. Entre otros, la incertidumbre de sus efectos sobre especies, hábitats y procesos ecológicos, y la consecuente dificultad para traducirlo a términos económicos; el desconocimiento de las sinergias con otras presiones ambientales; y la falta de conocimiento sobre el potencial de adaptación de los ecosistemas y sectores económicos.
This thesis has assessed the socio-economic effects of ocean acidification (OA) and sea warming in the Mediterranean Sea. These pressures share a common driver, namely the increase in anthropogenic emissions of CO2 since the Industrial Revolution. Their combination can be detrimental to endemic habitats and species, inter alia, coralligenous, bivalve molluscs and gorgonians. This, in turn, represents potential economic losses for bivalve mollusc aquaculture and scuba diving tourism sectors. This thesis has investigated such losses. To this end, the following tasks were undertaken: 1) development of a framework for studying the socio-economic impacts of OA in the Mediterranean Sea; 2) assessment of the potential vulnerability of Mediterranean bivalve mollusc aquaculture to climatic and non-climatic pressures by addressing the perceptions of the sector; 3) valuation of the impact of OA and sea warming on recreational benefits associated with diving in Mediterranean Marine Protected Areas (MPAs), featuring coralligenous habitat and gorgonians species; and 4) value transfer of welfare costs and tourism revenue losses due to both pressures by using an ecological model for various EU-Mediterranean MPAs. The main conclusions cover five insights. First, OA and sea warming are already perceivable in the Mediterranean Sea, and can become more pronounced throughout the century. Unique habitats like coralligenous, vermetid reefs and Posidonia oceanica meadows, and various groups of species (e.g., planktonic species, bivalve molluscs, gorgonians) are found to be vulnerable to both pressures. Likely ecosystem services to be affected include provision of food, the support of recreation activities, coastal protection, and carbon sequestration. Sea-based market activities such as fisheries (capture and aquaculture) and tourism, are sensitive to both pressures. Second, the results obtained from the questionnaires distributed among bivalve mollusc producers and representatives of Mediterranean MPAs show that OA is still poorly known, and that there is a high uncertainty about what it might imply in the future. Many respondents consider OA a low threat in comparison with other stressors, such as summer heat waves, a gradual increase in sea surface temperatures, or harmful algal blooms. Summer heat waves is a matter of great concern to the bivalve mollusc aquaculture sector, as it has already experienced various extreme events of this kind in the past years. A third insight is that OA and sea warming could affect the recreational value of Mediterranean diving areas with coralligenous. Results from a choice experiment for the MPA of Medes Islands (Spain) show potential welfare losses of scuba divers for scenarios involving a decrease of 50% and 100% in gorgonians (e.g., red coral, red gorgonian, white gorgonian) to equal -€17 and -€60/dive, respectively. In addition, the analysis of choice probabilities for selecting (or rejecting) dive experiences under various climatic scenarios indicate potential losses in tourism revenues, which in turn may affect local economies and funding of the MPA. Fourth, the previous results were extrapolated to other, similar EU-Mediterranean MPAs. This value transfer analysis combined information about welfare costs and tourism revenue losses with estimates generated by an ecological model of habitat suitability. The results show a likely decrease in the suitability of the coralligenous in the majority of the studied areas. Estimates for total welfare costs and tourism revenue losses were up to €36.6 and €20.780 million, respectively. Finally, assessment of the socio-economic effects of OA and sea warming presents various challenges associated with, inter alia, the uncertainty about the effects of these pressure on species, habitats and ecological processes, and the consequent difficulty to translate these into economic effects; the lack of understanding about the synergetic effects between multiple environmental pressures; and the uncertainty about the potential adaptation of ecosystems and economic sectors to future ocean conditions.

In the last decade, ocean acidification (OA) has become a major focus of scientific research. A significant fraction of anthropogenic carbon dioxide (C02) emissions is absorbed by the world's oceans, causing a decrease in pH and shifts in the carbonate chemistry of seawater towards increased CO2(aq) Many reef-building coral species obtain their algal symbionts from environmental populations of free-living Symbiodinium via a mechanism known as horizontal transmission. This thesis examined the effect ofOA upon the productivity and growth of four different phylotypes of Symbiodinium (AI, A2, A13 and BI) and also characterised the carbon concentrating mechanisms (CCMs) ofphylotypes A2 and A13, in culture (i.e. 'free-living'). The response to a doubling of pC02 to ~800 ppmv varied between phylotypes; A I and B I were relatively insensitive to OA whilst the productivity of A2 and the growth rate of A13 increased by 40% and 60%, respectively. This phylotype-specific response to OA is likely to affect population dynamics in free-living Symbiodinium, with further implications for those corals that obtain their symbionts via horizontal transmission. Furthermore, the actual mode of iC- acquisition was shown to differ between phylotypes, with A2 capable of indirect bicarbonate (HC03-) uptake, via the catalytic action of external carbonic anhydrase (eCA), whilst A13 was solely dependent upon the CO2(aq) fraction of the inorganic carbon pool in seawater. These differences in iC-acquisition provide the basis for the phylotype-specific effects of OA on these two phylotypes. Future studies will be able to build on these findings to examine the effect of OA upon a wider representation of the Symbiodinium genus and contrast their ability to regulate the CCM in response to changes in seawater pC02 and, ultimately, contribute towards a better understanding of the effects OA will have upon the form and function of coral reef ecosystems.

In recent years there has been increasing focus on predicting the potential effects of greenhouse gas driven global warming; this has proven to be a major challenge for science. In the last decade, there has been a major shift in research with growing scientific concern over the changing ocean carbonate chemistry as a result of ever increasing anthropogenic CO₂ emissions. Major changes to the basic chemistry of seawater, such as the water pH, are likely to have substantial implications for marine life in the future (Hardege et al., 2011). Research to date has focused largely upon those organisms that require calcium carbonate to build protective shells or skeletons (Orr et al., 2005). Using semelparous polychaetes, Platynereis dumerilii and Alitta succinea, it is shown that when exposed to pH levels forecasted to occur by 2100 (pH 7.8) survival, development, reproductive output and essential behaviours e.g. feeding and predator avoidance, are negatively impacted. A. succinea show severely reduced responses to natural chemical signals with subsequent low fertilisation and larval success. The ubiquity of chemical communication in the aqueous environment indicates that chemoreception disruption can potentially have dramatic consequences. Data show that if ocean acidification continues as predicted, marine chemoreception will have to adapt rapidly with potentially profound consequences for marine life and animal interactions. It is clear from this investigation that P. dumerilii and A. succinea are not capable of acclimatisation within one lifetime. Interestingly, P. dumerilii sampled and sequenced from a naturally occurring CO₂ vent in Ischia (Naples, Italy) are genetically different from other P. dumerilii populations within Europe. Individuals appear to show signs of adaptation in behavioural trials with few significant differences between pH treatments 8.2 and 7.8. Future studies are needed to ascertain how these organisms are adapted to life in low pH waters.

Elevations in atmospheric carbon dioxide (CO2) are anticipated to lead to the acidification of the world’s oceans over the next century. This thesis sought to understand the fate of the predator-prey interactions between the endemic predator, the Mulberry whelk Tenguella marginalba (Blainville, 1832) and their prey the native Sydney rock oyster Saccostrea glomerata (Gould, 1850) and the recently introduced Pacific oyster Crassostrea gigas (Thunberg, 1793) in a marine environment increasingly affected by elevated pCO2. It was predicted that predator-prey relationships will be altered by exposure to elevated pCO2 because 1) the energetic costs for T. marginalba to survive in an acidified environment will increase causing them to compensate by increasing their consumption rate of prey; 2) growth and physiological defences of S. glomerata and C. gigas will decrease and greater energy will be required for the maintenance of acid-base balance. It was also predicted that responses will vary between oyster species and within populations of oysters. This study provides evidence that alterations in predator-prey relationships will be complex. Responses of oysters to elevated CO2 were variable and dependent on the species, family line, ploidy and size which in some cases interacted with the presence of the whelk. This thesis provides evidence that utilising triploid breeding programs to produce oysters which can divert a greater proportion of their energy budget into growth and acid-base balance, may be a viable option to reduce the predicted impacts of elevated pCO2 on oyster aquaculture over this century. Preliminary evidence for selecting oyster family lines that are resilient to both elevated pCO2 and predation suggests that this may be a challenge and more research is required to determine whether this is a feasible option to help ‘climate-proof’ aquaculture industries and oyster populations in Australia and around the world.

Si conosce ancora poco riguardo la risposta delle comunità microbiche eterotrofe marine all’acidificazione oceanica e le conseguenze sulle reti trofiche e i cicli biogeochimici negli oceani. La maggior parte delle nostre conoscenze derivano da esperimenti manipolativi a breve termine. Studi in situ di aree caratterizzate da naturali variazioni di pH, possono aiutare a comprendere gli effetti dell’acidificazione oceanica a livello ecosistemico, prendendo in considerazione le complesse interazioni microbiche esistenti in ambienti naturali. In questo studio abbiamo investigato gli effetti dell’acidificazione oceanica sulla struttura e il funzionamento delle reti trofiche microbiche pelagiche e bentoniche e dei cicli biogeochimici in due aree costiere del Mediterraneo, caratterizzate da naturali condizioni di acidificazione, paragonabili agli scenari futuri previsti per l’anno 2100 e 2500. A Presidiana (Sicilia) la naturale acidificazione era dovuta ad un input terrestre di acque a bassa salinità, nell’isola di Ischia era associata all’attività di vents vulcanici. I nostri risultati hanno mostrato che le condizioni di acidificazione causavano nei sedimenti un aumento della biomassa algale e delle attività enzimatiche extracellulari, con conseguente diminuzione del contenuto di materia organica a valori estremi di pH (<7). Bassi valori di pH in acqua causavano una riduzione della biomassa fitoplanctonica e della materia organica particellata e, associati a bassi valori di salinità, avevano un effetto negativo sulle attività enzimatiche extracellulari. Tuttavia in entrambi i sistemi investigati, valori di pH attesi per il 2100 hanno mostrato un significativo impatto su procarioti e virus pelagici e bentonici e sulle loro interazioni, causando un aumento della produzione virale e della mortalità procariotica indotta dai virus. L’infezione virale era favorita ulteriormente dall’aumento dell’attività enzimatica specifica delle singole cellule procariotiche. Al maggiore impatto virale era associato anche un cambiamento nella composizione di comunità batteriche e una diminuzione di diversità. Riduzioni estreme di pH sono risultate invece sfavorevoli alle attività virali influenzando negativamente le interazioni virus-procarioti e riducendo la pressione virale sulle comunità microbiche.
We still know little about the response of heterotrophic microbial communities to ocean acidification and the consequences for marine food webs and biogeochemical cycles. Most of our knowledge is derived from short-term perturbation experiments. In situ observational studies, exploiting natural pH gradients, can help to understand the ecosystem level effects of ocean acidification, taking into account the complex microbial interactions and environmental conditions. In this study we investigated the effects of ocean acidification on the structure and functioning of pelagic and benthic microbial food webs and biogeochemical cycling in two coastal areas of the Mediterranean Sea, characterized by naturally acidified conditions, comparable to near future (i.e., 2100) and extreme (i.e., 2500) scenarios. At Presidiana (Sicily) the natural acidification was due to freshwater input from inland, at Island of Ischia was associated with volcanic CO2 vents. Our results showed that in the sediment the acidification caused an increase of algal biomass and of extracellular enzymatic activities, with a consequently decrease of biochemical components at extremely low pH values (<7). Low pH values in seawater caused a reduction of phytoplankton biomass and of suspended organic matter and, associated to low salinity, affected negatively the extracellular enzymatic activities. However in both investigated systems, pH values expected for a near future scenario, had a significant impact on pelagic and benthic prokaryotes and viruses and on their interactions, increasing viral production and prokaryotic mortality induced by viruses. The increase of viral infection was favoured also by enhanced specific metabolic activity of single prokaryotic cells. The enhanced viral impact was associated with an alteration of bacterial assemblage composition and a reduction of bacterial diversity. Conversely extremely low pH values affected negatively the viral activity and the virus-prokaryotes interaction, reducing the viral pressure on microbial assemblage. Further studies are needed to investigate the potential impact of global climate changes on future oceans and their biogeochemical processes.

The need to understand future changes in marine ecosystems has become critically important as increasing atmospheric carbon dioxide (CO₂) drives rapid ocean acidification (OA). OA may improve or reduce the performance of marine species, and the relative impacts on interacting species will largely determine changes at the community level. The goal of this thesis was to determine the effects of acidification on predator-prey interactions between red sea urchins (Strongylocentrotus franciscanus) and sunflower stars (Pycnopodia helianthoides), a key predator-prey pair in Northeast Pacific kelp forest ecosystems. I tested this question using laboratory mesocosm experiments. Sea urchins were acclimated to ambient (pCO₂ ~ 500 μatm, pH ~ 8.0) or acidified (pCO₂ ~ 1000 μatm, pH ~ 7.7) conditions, with or without a caged sea star, for 22 weeks in a recirculating seawater system. In Chapter 2, I investigated the effects of OA on the growth, calcification, and feeding rate of P. helianthoides. High CO₂ had a significant positive effect on sea star growth, but no effect on calcified tissue mass. In addition, the consumption rate of turban snails (Chlorostoma funebralis) by sea stars was significantly higher in the high CO₂ treatment. In Chapter 3, I examined the effects of OA on the responses of S. franciscanus to sea star cues. Predator presence and high CO₂ negatively and additively affected sea urchin growth rates, but did not affect alarm responses to predator cues. Significantly higher grazing rates on kelp (Macrocystis pyrifera) were also observed in the presence of predators. Predators, but not CO₂, had a significant negative effect on urchin calcified mass. Urchin spine length was also significantly reduced under acidified conditions. Overall, these findings suggest P. helianthoides responds positively to ocean acidification, but S. franciscanus may suffer reduced fitness at seawater pCO₂ levels predicted for the end of the century. Differential effects of ocean acidification on this predator-prey pair could increase the strength of the trophic interaction and lead to stronger top-down control in the future.
Science, Faculty of
Zoology, Department of
Graduate

The current increase in the atmospheric CO2 concentration results in two major consequences in the marine environment: an increase of the sea surface temperature (0.7 °C since pre-industrial times) and a decreased seawater pH. This decrease is being measured continuously in different parts of the world and ranges from -0.0017 to -0.04 units per year according to the location considered. Based on CO2 emissions models provided by the IPCC, it was predicted that the average open ocean pH would decrease further by 0.4 units by 2100 and 0.8 by 2300 (corresponding to about a three-fold and six-fold increase of the proton concentration). Also, saturation states of seawater for the different forms of calcium carbonate, such as calcite, magnesium calcite and aragonite which are produced by calcifying marine organisms, are decreasing and consequently the saturation horizons of these minerals are shoaling. Today, some environments are characterized by pH values lower than the average open ocean pH. These are intertidal rock pools, upwelling zones, the deep-sea and CO2 vents. In these environments, pH is either constantly low or fluctuates. Those changes are either due to biological activity, geological CO2 leakage, or water masses movements. Within these environments, it has been hypothesized that organisms could be adapted or acclimatized to low pH values such as those predicted for the near-future.

Tolerance to ocean acidification in metazoans is linked to their acid-base regulation capacities when facing environmental hypercapnia (i.e. increased CO2 concentration in the surrounding environment). The latter may result in a hypercapnia of the internal fluids and a concomitant acidosis (i.e. reduced pH of the internal fluids due to the dissociation of CO2 in this case). Organisms have two buffer systems allowing the compensation of this acidosis: the CO2-bicarbonate and the non-bicarbonate buffers. Homeostasis of the internal fluids thanks to these systems is essential for the proper functioning of enzymes and processes. As hypometabolic calcifying osmoconformers, three of the characteristics conferring a relative vulnerability to ocean acidification, echinoderms are considered “at risk” for the near-future conditions. Nonetheless, post-metamorphic (juveniles and adults) echinoderms inhabit all environments showing naturally low pH. Furthermore, sea urchins which are highly calcified (compared to sea stars or sea cucumbers) are also found in these environments. This suggests that echinoderms have strategies to adapt or acclimate to low pH environments. Recent studies indicated that while sea urchins are able to regulate their coelomic (extracellular) fluid by accumulation of bicarbonate, sea stars seem to tolerate the acidosis linked to environmental hypercapnia. However, this information was obtained on a reduced number of species and significant interspecific differences were evidenced. Some taxa have not been investigated at all. Furthermore, several aspects of the acid-base physiology were unexplored, like the buffering capacity of the extracellular fluid and the origin of carbon within these fluids.

Accordingly, the goal of this study was to characterize the acid-base physiology in post-metamorphic echinoderms of different taxa in order to understand their response to ocean acidification.

The acid-base regulation capacities within the different echinoderm taxa were compared. A method was designed to measure the total alkalinity in small volumes (500 µl) of the main extracellular fluid (the coelomic fluid). This study showed that regular euechinoids have an increased buffer capacity in their coelomic fluid compared to seawater and the other echinoderm groups. In sea urchins, bicarbonate and non-bicarbonate buffers come into play, the former playing the major role. This buffer capacity was increased in fed individuals compared to fasted ones and increased further when seawater pH was lowered.

The acid-base regulation capacities of sea urchins from different taxa were investigated. Regular euechinoids possess an increased buffer capacity of the coelomic fluid allowing them to maintain a higher pH compared to cidaroids at current seawater pH. This pattern was found for temperate, tropical and Antarctic sea urchins. Data was also obtained for irregular echinoids which also showed a particularly low extracellular pH and a buffer capacity close to seawater like cidaroids. When exposed to reduced seawater pH (8.0, 7.7, and 7.4) for 4-6 weeks, regular euechinoids showed an increasing buffer capacity of the coelomic fluid accompanied by a homeostasis of the pH. On the contrary, cidaroids showed no changes in their acid-base status whatever the seawater pH (8.0 to 7.4). The origin of coelomic fluid carbon, investigated by stable carbon isotope analysis, also differs according to taxa. The δ13CDIC of regular euechinoids evidenced a mixing between CO2 from metabolic origin and that from the surrounding seawater. This is further supported by the correlation between the seawater signal of reduced pH conditions (modified by the addition of industrial gas, changing the δ13C to more negative values) and that of the coelomic fluid. On the other hand, cidaroids exhibit a signal reflecting principally metabolic CO2 (very negative δ13C), and the δ13C did not change under varying pH conditions (i.e. did not adapt to the seawater δ13CDIC signature). For irregular echinoids, the carbon origin is unclear as some species show signals close to that of regular euechinoids whereas others are similar to cidaroids.

The impact of acid-base regulation was investigated by testing the effect of ocean acidification on the mechanical properties of the skeleton (test plates) in the sea urchin Paracentrotus lividus. Individuals from intertidal pools, CO2 vents and a one year acidification experiment (pH 8.0, 7.9 and 7.7) were compared. Only the intertidal pool individuals showed a difference of the Young’s modulus and fracture forces of their plates. Sea urchins from the tide pool with the largest pH fluctuations showed a lower stiffness and strengthened test. On the contrary, sea urchins from CO2 vents and experimental acidification did not display any differences in the several mechanical properties tested. We suggest that the different food qualities (calcified vs. uncalcified algae) in the different tide pools significantly contributed to the observed difference.

The acid-base regulation ability of sea cucumbers was assessed in two species from contrasted habitats (mangrove intertidal vs. coral reef species). These organisms underwent acidosis of the coelomic fluid when exposed to reduced seawater pH for a short time (6 to 12 days). The δ13C signal of the coelomic fluid mirrored that of the surrounding seawater in all conditions, indicating that the CO2 accumulated (cause of the acidosis) comes also from the seawater. This is still unexplained to date. However, metabolic processes such as respiration and ammonium excretion rates were not affected. No difference was evidenced between the two species.

The results obtained in this study compiled with data from the literature indicate that post-metamorphic echinoderms have contrasted acid-base physiology with most regular euechinoids compensating the coelomic fluid pH by accumulation of bicarbonate ions (and possibly ophiuroids also), cidaroids and at least one regular euechinoid (Arbacia lixula) having a naturally low coelomic fluid pH which is not affected by acidification, and sea stars and sea cucumbers which do not compensate their coelomic fluid pH when submitted to acidified seawater. In regular euechinoids, negative effects are linked to resource allocation with growth usually being reduced in favor of acid-base regulation mechanisms. Starfish and sea cucumbers appear as resilient to acidification, with very few functions being negatively impacted. In conclusion, it seems that post-metamorphic echinoderms studied so far will not be particularly at risk when facing ocean acidification levels expected by 2100. Furthermore, tolerance to ocean acidification does not seem linked to the present day ambient pH regime. Nevertheless, more studies need to be carried out on brittle stars and sea cucumbers to confirm preliminary results, as well as crinoids which have not been investigated to date. Long-term exposure experiments to estimate energy budget changes as well as more assessments of evolutionary potential in echinoderms are crucially needed./L’augmentation actuelle de la concentration en CO2 atmosphérique a deux conséquences majeures dans l’environnement marin :une augmentation de la température des eaux de surface (0.7°C depuis l’époque préindustrielle) et une diminution du pH de l’eau de mer. Cette diminution est mesurée continuellement dans différentes régions du monde et varie de -0.0017 à -0.04 unités de pH par an en fonction du site considéré. Basé sur des modèles d’émissions de CO2 du GIEC, il a été prédit que le pH moyen de l’océan diminuerait encore de 0.4 unités d’ici 2100 et 0.8 d’ici 2300 (correspondant à une augmentation de la concentration en protons d’environ 3 fois et 6 fois). De même, les états de saturation de l’eau de mer vis-à-vis des différentes formes de carbonate de calcium, telles que la calcite, la calcite magnésienne et l’aragonite produites par les organismes calcifiants, sont en train de diminuer et par conséquent, les horizons de saturation remontent vers les eaux de surface. Aujourd’hui, certains environnements sont caractérisés par des valeurs de pH plus basses que celle de l’océan. Ceux-ci sont les mares intertidales, les zones d’upwelling, l’océan profond et les évents volcaniques. Dans ces environnements, le pH est soit constamment bas ou fluctue. Ces changements sont soit dû à une activité biologique, une fuite de CO2 géologique, ou au mouvement des masses d’eau. Dans ces environnements, il a été suggéré que les organismes pourraient être adaptés ou acclimatés à des valeurs basses de pH, telles que celles prédites pour le futur proche.

La tolérance à l’acidification des océans chez les métazoaires est liée à leur capacité de régulation acide-base lorsqu’ils sont exposés à une hypercapnie environnementale (c’est-à-dire, une augmentation de la concentration en CO2 dans l’environnement entourant l’organisme). Ce phénomène peut résulter en une hypercapnie des liquides internes et une acidose concomitante (c’est-à-dire, un pH des liquides internes réduit dû à la dissociation du CO2 dans ce cas précis). Les organismes ont deux systèmes tampons leur permettant de compenser l’acidose :les tampons CO2-bicarbonate et non-bicarbonate. L’homéostasie des liquides internes grâce à ces systèmes est essentielle pour le fonctionnement correct des enzymes et processus. En tant qu’osmoconformes calcifiant hypométaboliques, trois caractéristiques menant à une certaine vulnérabilité face à l’acidification des océans, les échinodermes sont considérés « à risque » pour les conditions du futur proche. Cependant, les échinodermes post-métamorphiques (juvéniles et adultes) occupent tous les environnements montrant un pH faible naturellement. De plus, les oursins qui sont hautement calcifiés (par rapport aux étoiles de mer ou aux concombres de mer) sont également retrouvés dans ces environnements. Ceci suggère que les échinodermes ont des stratégies d’adaptation ou d’acclimatation à ces environnements à bas pH. Alors que des études récentes montrent que les oursins sont capables de réguler le pH du liquide cœlomique (extracellulaire) par l’accumulation de bicarbonates, les étoiles semblent tolérer l’acidose liée à l’hypercapnie environnementale. Néanmoins, ces informations ont été obtenues sur un petit nombre d’espèces et des différences interspécifiques significatives ont été mises en évidence. Certains taxa n’ont pas été étudié du tout. Par ailleurs, différents aspects de la physiologie acide-base sont inexplorés, tels que la capacité tampon du liquide extracellulaire et l’origine du carbone dans ces liquides.

Par conséquent, le but de cette étude était de caractériser la physiologie acide-base chez les échinodermes post-métamorphiques de différents taxa afin de comprendre leur réponse à l’acidification des océans.

Les capacités de régulation acide-base au sein des différents groupes d’échinodermes ont été comparées. Une méthode a été mise au point afin de mesurer l’alcalinité totale dans de petits volumes (500 µl) de liquide extracellulaire (le liquide cœlomique). Cette étude démontra que la capacité tampon du liquide cœlomique des euéchinoïdes réguliers est accrue comparée à celle de l’eau de mer ainsi que celle des autres groupes d’échinodermes. Dans les oursins, les tampons bicarbonate et non-bicarbonate entrent en jeux, le premier étant majoritaire. Cette capacité tampon est augmentée chez les individus nourris par rapport à ceux à jeuns et est augmentée plus encore lorsque le pH de l’eau de mer est diminué.

Les capacités de régulation acide-base ont été étudiées plus spécifiquement dans les différents groupes d’oursins. Les euéchinoïdes réguliers possèdent une capacité tampon accrue du liquide cœlomique leur permettant de maintenir un pH élevé comparé aux oursins cidaroïdes, au pH de l’eau de mer actuel. Ce patron se retrouve dans les oursins tempérés, tropicaux et antarctiques. Des données ont également été obtenues pour les oursins irréguliers qui ont également un pH extracellulaire particulièrement bas et une capacité tampon proche de celle de l’eau de mer comme les cidaroïdes. Lorsqu’ils sont exposés à un pH de l’eau de mer réduit (7.7 et 7.4 par rapport à 8.0) pour 4 à 6 semaines, les euéchinoïdes réguliers ont montré une augmentation de la capacité tampon du liquide cœlomique accompagnée d’une homéostasie du pH de ce liquide. A l’inverse, les cidaroïdes n’ont montré aucune modification de leur statut acide-base quel que soit le pH (8.0 à 7.4). L’origine du carbone du liquide cœlomique, étudié par analyse des isotopes stables du carbone, diffère également en fonction du groupe. Le δ13CDIC des euéchinoïdes réguliers met en évidence un mélange entre du CO2 d’origine métabolique et celui de l’eau environnante. Ceci est également démontré par la corrélation entre le signal de l’eau de mer dont le pH est réduit (modifié par l’ajout de CO2 industriel, changent le δ13C vers des valeurs plus négatives) et celui du liquide cœlomique. En revanche, les cidaroïdes montrent un signal reflétant principalement celui du CO2 métabolique (δ13C très négatif), et le δ13C n’est pas influencé par des conditions de pH variées (c’est-à-dire, qu’il ne s’adapte pas à la signature du δ13CDIC de l’eau de mer). Pour les oursins irréguliers, l’origine du carbone est incertaine puisque certaines espèces montrent un signal proche de celui des euéchinoïdes réguliers et d’autres similaire à celui des cidaroïdes.

L’impact de la régulation acide-base a été étudié en testant l’effet de l’acidification des océans sur les propriétés mécaniques du squelette (plaques squelettiques) de l’oursin Paracentrotus lividus. Des individus de mares intertidales, d’évents volcaniques et d’une expérience d’acidification d’un an (pH 8.0, 7.9 et 7.7) ont été comparés. Seuls les individus des mares intertidales montrèrent une différence pour le module de Young et la force des fractures des plaques. Les oursins venant de la mare intertidale montrant les plus grandes variations de pH avaient une rigidité plus faible et un squelette renforcé. A l’inverse, les oursins des évents volcaniques et de l’expérience d’acidification n’ont montrés aucune différence dans les diverses propriétés mécaniques étudiées. Nous suggérons que les variations en termes de qualité de nourriture (algues calcifiées vs. non-calcifiées) dans les différentes mares intertidales ont contribués de manière significative à la différence observée.

L’habilité des concombres de mer à réguler leur balance acide-base a été évaluée dans deux espèces d’habitats contrastés (espèce intertidale des mangroves vs. subtidale des récifs coralliens). Ces organismes ont subis une acidose du liquide cœlomique lorsqu’ils ont été exposés à un pH réduit de l’eau de mer pour une courte durée (6 à 12 jours). Le signal δ13C du liquide cœlomique reflétait celui de l’eau environnante dans toutes les conditions, indiquant que le CO2 accumulé (cause de l’acidose) venait de l’eau. Ceci est encore inexpliqué à l’heure actuelle. Cependant, les processus métaboliques tels que la respiration ou l’excrétion d’ammonium n’ont pas été affecté. Aucune différence n’a été observée entre les deux espèces.

Les résultats obtenus dans cette étude compilés avec ceux de la littérature indiquent que les échinodermes post-métamorphiques ont une physiologie acide-base contrastée avec la plupart des euéchinoïdes réguliers qui compensent le pH du liquide cœlomique par l’accumulation d’ions bicarbonates (et peut-être les ophiures aussi), les cidaroïdes et au moins un euéchinoïde régulier (Arbacia lixula) qui ont naturellement un pH du liquide cœlomique bas et qui ne sont pas affectés par l’acidification, et les étoiles de mer et les concombres de mers qui ne compensent pas le pH du liquide cœlomique lorsqu’ils sont soumis à une eau acidifiée. Chez les euéchinoïdes réguliers, des effets négatifs sont liés à un changement de l’allocation des ressources avec souvent un taux de croissance réduit en faveur des mécanismes de régulation acide-base. Les étoiles de mer et les concombres de mer apparaissent plus tolérants à l’acidification, avec peu de fonctions négativement impactées. En conclusion, il semble que les échinodermes post-métamorphiques étudiés jusqu’à présent ne seront pas particulièrement à risque lorsqu’ils seront exposés au niveau d’acidification attendu pour 2100. De plus, la tolérance à l’acidification des océans ne semble pas liée au régime de pH subit actuellement. Cependant, plus d’études doivent être menées sur les ophiures et les concombres de mer afin de confirmer les résultats préliminaires, ainsi que sur les crinoïdes qui n’ont à l’heure actuelle pas encore été étudiés. Des expériences à long terme afin d’estimer le budget énergétique des organismes ainsi que plus d’évaluations du potentiel d’évolution chez les échinodermes sont absolument nécessaires.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Ocean acidification (OA) together with other anthropogenic perturbations is projected to dramatically alter marine environments over the coming centuries. The vast majority of marine species reproduce by freely spawning sperm directly into the water column, where fertilisation can then either be external or a female can draw sperm into a burrow, brooding chamber or onto her external surface. Hence, sperm are now being released into rapidly changing seawater conditions. In this thesis, I firstly assess what is currently known on the potential for OA and other anthropogenic stressors to influence freely spawned sperm in marine invertebrate taxa. I then present a series of experimental chapters investigating the influence of OA, as a single stressor or in conjunction with a second stressor, copper, on sperm function, physiology and competitive fertilisation performance in a range of invertebrate taxa. My research demonstrates that sperm are vulnerable to the projected changes in seawater carbonate chemistry under OA, with responses observed at all biological levels from sperm physiology, swimming performance, fertilisation ecology and sperm competitiveness. In a multi-stressor experiment on polychaete gametes and larvae, I provide empirical evidence that changes to seawater pH under OA can alter the susceptibility of early life stages including sperm, to the common coastal pollutant copper. Sperm DNA damage increased by 150 % and larval survivorship was reduced by 44 % in combined exposures, than when exposed to copper alone. As a single stressor OA also acted to significantly reduce Arenicola marina sperm swimming speeds and fertilisation success. This work was followed up with a mechanistic investigation of A. marina sperm swimming performance under OA conditions. I found that the length of time between spawning and fertilisation can strongly influence the impact of OA on sperm performance. Key fitness-related aspects of sperm functioning declined after several hours under OA conditions, and these declines could not be explained by changes in sperm ATP content, oxygen consumption or viability. In a final set of experiments, I ran a set of paired competitive fertilisation trials in the sea urchin, Paracentrotus lividus. In addition to reducing fundamental sperm performance parameters, OA conditions affected competitive interactions between males during fertilisation, with potential implications for the proportion of offspring contributed by each male under the new conditions. This work suggests that the ‘best’ males currently may not be the most competitive under OA. Overall this body of work reveals a series of significant changes to sperm performance under OA that might act to perturb sperm functioning in future oceans.

For decades, humans have impacted marine ecosystems in a variety of ways including contamination by pollution, fishing, and physical destruction of habitats. Global change has, and will, lead to alterations in in a number of abiotic factors of our ocean in particular reduced oxygen saturation, salinity changes, elevated temperature (ocean warming or OW) and elevated carbon dioxide (ocean acidification or OA). Now and in the future, OA and OW will operate together with local anthropogenic drivers such as oil pollution. And yet, at present, very little is known about their potential combined interactive effects on physiological performance and tolerance of marine organisms. Therefore, multiple driver experiments are required if we are to understand and predict future vulnerability of species, populations and ecosystems. Early life stages of invertebrates are generally considered most vulnerable to environmental stress. However, few studies consider the combined effects OA and OW on survival and growth during early development of marine invertebrates, and to our knowledge, there is no information on the additional effects of oil pollution. Therefore, the aim of this thesis was to investigate the effects of combined exposure to OA, OW, and incorporating local drivers such as oil pollution on the development, morphology and physiology of three economically and ecologically important marine invertebrates. These are Northern shrimp Pandalus borealis, Northern krill Meganyctiphanes norvegica, and the green sea urchin Strongylocentrotus droebachiensis. All are cold-water species, assumed to have a narrower tolerance than more temperate species, and so could be particular sensitive to combined stressor affects. Both Northern krill and to a lesser extent Northern shrimp larvae survived experimental conditions, mirroring those predicted under a future global change scenario (combined OA and OW exposure). Neither was hatching success affected. Both shrimp and krill larvae exhibited accelerated developmental rates and incurred greater maintenance costs as a result of exposure to these stressors. Shrimp larvae showed accelerated developmental rates (-9 days), increased metabolic rates (+20 %), and increased feeding rates (+20 %), but reduced growth (- 9 %) when exposed to OW compared with the control. OA increased development rate but only at the control temperature. Although juvenile mortality of krill was not affected by predicted OA/OW conditions, metabolic rate increased significantly (+ 36 %), as did larval developmental rate, while number of moults, feeding rate and growth (- 67 %) decreased significantly (- 67 %, - 60 % and -8 % respectively). Accelerated development was accompanied by greater maintenance costs possibly due to experience a mismatch between energy supply and demand. Both species had an excess of food, and so growth reduction was more likely to be associated with higher metabolic demands in the future global change treatments. Food shortage in situ, due to variable food availability in the sea and/or mismatch with key prey species (algae and zooplankton) could result in more negative effects on growth and ultimately survival. Green sea urchins were also able to survive OA exposure, without detectable effects on hatching success. However, at day 44 post-fertilization, larval body length in the OA treatment was 9 % lower compared to the control. Furthermore, there was a significant tendency of urchin larvae to increase swimming activity in the OA conditions that might indicate compensatory feeding. Elevated maintenance and repair costs as a result of exposure to multi-stressors affected the energy budget of all the three species studied here resulting in reduced growth. Global drivers (OA and OW) resulted in trade-offs with more energy reallocated to swimming activity and metabolism, rather than growth. Exposure to oil reduced the acquisition of energy by reduced feeding which in turn resulted in less energy being available for growth. Both shrimp and sea urchin larvae showed reduced activity and feeding when exposed to oil. It is possible that the reduced swimming activity observed may be due to a narcotic effect of the oil. Furthermore, early stage sea urchin larvae showed increased mortality when exposed to oil while the older larvae did not, indicating a stage specific toxicity to oil for sea urchin larvae. The combination of global drivers and oil pollution acted additively on growth for both sea urchin and shrimp larvae. The impact of combined drivers on the size of shrimp larvae was equal the sum of the negative impacts observed for each driver: a 5 % reduction when exposed to OA and OW, a 9 % reduction when exposed to oil, and a cumulative 15 % reduction when exposed to all stressors. Similarly, the impact of combined drivers on the size of sea urchin larvae was equal to the sum of the negative impacts observed for each driver: a 14 % reduction when exposed to OA, a 9 % reduction when exposed to oil, and a 21 % reduction when exposed to all drivers. Therefore, the study demonstrated the additive physiological effects of OA, OW and a contaminant, and indicated that larval (sea urchin and shrimp) resilience to future changes (i.e. pollution) could be greatly reduced if larvae were already energy limited and severely stressed (reduced development) as a result of exposure to the global drivers. This study therefore shows the importance that the effective management of local drivers such as oil pollution could have against the backdrop of OA and OW, and emphasises that it is important to study impacts of toxicants, such as an oil pollution, in the context of predicted changes in the environment, as OW and OA are becoming major concerns. Finally, the fact that some local and global drivers seem to act additively should encourage local managers to act on local driver regulations, to obtain positive effects on local populations and environment and thereby rendering them more resilient to the negative impacts of future global drivers.

Increasing atmospheric CO2 concentrations associated with climate change will likely influence a wide variety of ecosystems. Terrestrial research has examined the effects of increasing CO2 concentrations on the functionality of plant systems; with studies ranging in scale from the short-term responses of individual leaves, to long-term ecological responses of complete forests. While terrestrial plants have received much attention, studies on the responses of marine plants (seagrasses) to increased CO2(aq) concentrations remain relatively sparse, with most research limited to small-scale, ex situ experimentation. Furthermore, few studies have attempted to address similarities between terrestrial and seagrass responses to increases in CO2(aq). The goals of this dissertation are to expand the scope of marine climate change research, and examine how the tropical seagrass, Thalassia testudinum responds to increasing CO2(aq) concentrations over multiple spatial and temporal scales. Manipulative laboratory and field experimentation reveal that, similar to terrestrial plants, seagrasses strongly respond to increases in CO2(aq) concentrations. Using a novel field technique, in situ field manipulations show that over short time scales, seagrasses respond to elevated CO2(aq) by increasing leaf photosynthetic rates and the production of soluble carbohydrates. Declines in leaf nutrient (nitrogen and phosphorus) content were additionally detected, paralleling responses from terrestrial systems. Over long time scales, seagrasses increase total above- and belowground biomass with elevated CO2(aq), suggesting that, similar to terrestrial research, pervasive increases in atmospheric and oceanic CO2(aq) concentrations stand to influence the productivity and functionality of these systems. Furthermore, field experiments reveal that seagrass epiphytes, which comprise an important component of seagrass ecosystems, additionally respond to increased CO2(aq) with strong declines in calcified taxa and increases in fleshy taxa. Together, this work demonstrates that increasing CO2(aq) concentrations will alter the functionality of seagrass ecosystems by increasing plant productivity and shifting the composition of the epiphyte community. These results have implications for future rates of carbon storage and sediment production within these widely distributed systems.

The following thesis explores the physiological effects on European sea bass (Dicentrarchus labrax) and shore crabs (Carcinus maenas) resulting from the dissolution of anthropogenic carbon dioxide (CO2) into seawater: known as ocean acidification. It assesses how ocean acidification, characterised by elevated seawater pCO2 (1200 µatm) and lowered pH (~7.7), affect the internal chemistry of these animals through the homeostatic process of acid-base regulation. Control conditions used for comparison were close to current ocean average values for CO2 (~400 µatm) and pH (8.2). The proficiency and magnitude of these compensatory mechanisms was explored. Both sea bass and shore crabs were found to be highly effective acid-base regulators and employed the same strategy to compensate the hypercapnia-induced respiratory acidosis: namely an elevation of extracellular bicarbonate (HCO3-). It then considers how these regulatory mechanisms both affect, and are affected by, simultaneous exposure to a ubiquitous coastal metal contaminant, copper. Evidence for a hitherto undocumented protective effect of elevated HCO3- against copper-induced DNA damage was found to be afforded to both sea bass and shore crab cells. DNA damage was used as a sensitive toxicity marker and blood cells were used as proxies for other internal tissues. Erythrocytes exposed in vitro (2 h) to copper (45 µg/L) showed significant DNA damage under control [HCO3-] (6 mM) but were completely protected when exposed under high [HCO3-] (12 mM). A similar protective effect was apparent in crabs under in vivo exposure (14 d) to 10 µg/L waterborne copper. Conversely, during exposure to higher waterborne copper concentrations (sea bass: 80 µg/L, shore crabs: 40 µg/L), animals showed a severe or total inhibition of acid-base regulatory ability in the face of simultaneously elevated seawater CO2 (1200 µatm). The downstream effects of longer-term (28 d) exposure to high CO2 and copper, both individually and in combination was assessed. Food conversion efficiency (FCE), growth and copper accumulation were quantified in juvenile sea bass as economically relevant endpoints. Growth and FCE remained unaffected by either stressor and copper was not accumulated in the muscle tissue: pertinent to human consumption. As a bi-product of this longer term study assessment of gut calcium carbonate production rates in these animals was possible, providing some of the first evidence of excretion rates in fish fed on naturally high calcium diets. A directly proportional influence of feeding rate on gut carbonate excretion rates as a result of increased dietary calcium was observed, and novel evidence provided of the proportional contribution of dietary and seawater calcium to excreted carbonate. Both findings have considerable application to global models of fish contribution to the oceanic carbon cycle.

Coral reefs are one of the most economically important ecosystems on the planet. Despite their great contribution to the world economy, anthropogenic influence via carbon dioxide emissions is leading to unprecedented changes with concerns about subsequent negative impacts on reefs. Surface ocean pH has dropped 0.1 units in the past century; in spite of this rapid shift in oceanic chemistry, it is unclear if individual species or life stages of Caribbean stony corals will be more sensitive to ocean acidification (OA). Examined is the relationship between CO2-induced seawater acidification, net calcification, photosynthesis, and respiration in three model Caribbean coral species: Orbicella faveolata, Montastraea cavernosa, and Dichocoenia stokesi, under near ambient (465 ± 5.52 ppm), and high (1451 ± 6.51 ppm) CO2 conditions. A species specific response was observed for net calcification; D. stokesi and M. cavernosa displayed a significant reduction in CaCO3 secreted under OA conditions, while O. faveolata fragments showed no significant difference. At the cellular level, transmission electron micrographs verified that all species and treatments were actively calcifying. Skeletal crystals nucleated by O. faveolata in the high CO2 treatments were statistically longer relative to controls. These results suggest that the addition of CO2 may shift the overall energy budget, causing a modification of skeletal aragonite crystal structures, rather than inhibiting skeletal crystal formation. Consequential to this energy shift, Orbicella faveolata belongs in the category of Scleractinian corals that exhibit a lower sensitivity to ocean acidification.

As human activities continue to generate accelerating levels of carbon dioxide emissions, the world’s oceanic resources are threatened by variability in seawater chemistry, known as ocean acidification. Recent increases in atmospheric carbon dioxide have resulted in decreased carbonate ion concentrations and ocean pH levels, leading to increasingly acidic waters. The exact consequences of these chemical changes on ecosystems and individual species are difficult to predict; however, research has shown that economically valuable calcifying species will experience reduced reproductive fitness and population declines. Ocean acidification, therefore, poses an immediate risk to both fish stocks and fishery industries. From a local perspective, individual regions will need to implement dynamic management strategies to prepare for anticipated economic consequences. In a global context, international cooperation is required for further research and collaborative efforts must be made to reduce future acidification.

Recent concern over the effects of ocean acidification upon calcifying organisms in the modern ocean has highlighted the aragonitic shelled thecosomatous pteropods as being at a high risk. Laboratory studies have shown that increased pCO2, leading to decreased pH and low carbonate concentrations, has a negative impact on the ability of pteropods to calcify and maintain their shells. This study presents the micropalaeontological analysis of marine cores from the Caribbean Sea, Mediterranean Sea and Indian Ocean. Pteropods, heteropods and planktic foraminifera were picked from samples to provide palaeoenvironmental data for each core. Determination of pteropod calcification was made using the Limacina Dissolution Index (LDX) and the average shell size of Limacina inflata specimens. Pteropod calcification indices were compared to global ice volume and Vostok atmospheric CO2 concentrations to determine any associations between climate and calcification. Results show that changes in surface ocean carbonate concentrations throughout the Late Pleistocene did affect the calcification of thecosomatous pteropods. These effects can be detected in shells from marine sediments that are located well above the aragonite lysocline and have not undergone post-depositional dissolution. The results of this study confirm the findings of laboratory studies, showing a decrease in calcification during interglacial periods, when surface ocean carbonate concentrations were lower. During glacial periods, calcification was enhanced due to the increased availability of carbonate. This trend was found in all sediments studied, indicating that the response of pteropods to past climate change is of global significance. These results demonstrate that pteropods have been negatively affected by oceanic pH levels relatively higher and changing at a lesser rate than those predicted for the 21st Century. Results also establish the use of pteropods and heteropods in reconstructing surface ocean conditions. The LDX is a fast and appropriate way of determining variations in surface water carbonate saturation. Abundances of key species were also found to constrain palaeotemperatures better than planktic foraminifera, a use which could be further developed.

This text is presented in conjunction with my exhibition Crossing the Ecoline and is a visual response to changing levels of ocean acidification. My art making is informed by the processes of dispersal and dissolution that occur at the point where the absorption of carbon dioxide takes place between the atmosphere and the ocean. This project is of an interdisciplinary nature and traverses art and science - both technically and through collaboration. By working in close consultation with marine scientists I hope to draw attention to the little-known issue of ocean acidification through creative means. Through the consideration of materials and processes I aim to bring attention to where billions of microorganisms called phytoplankton live. The project is concerned with the idea of the edge: boundary or border as a conceptual notion, as well as through my art making practice, its interdiscplinarity and subject matter.

Since the 1800s, carbon dioxide emissions due to human activities have contributed significantly to the amount of carbon in the atmosphere. Approximately a third of this carbon is absorbed by the ocean, through air-sea fluxes at the ocean surface (Sabine, 2004). Increased CO2 has changed the carbon chemistry of the ocean and hence the pH. pH is expected to drop by 0.4 by the year 2100. It is unclear how this lower pH will affect carbon cycling and sequestration with respect to the biological carbon pump. Most studies have focused on open ocean phytoplankton or bacterial communities in large, stationary mesocosms. Few studies have coupled both phytoplankton and bacterial processes and even fewer have investigated coastal communities, where pH and pCO2 can vary drastically. This study focused first on developing and evaluating a mesocosm and alternative method for elevating pCO2. The second goal was to determine how potential changes in phytoplankton DOC release and community structure and the resulting carbon pool may affect bacterial secondary production and ectoenzyme activity in a natural coastal community. Mesocosms aimed to mimic natural pCO2 fluctuations by maintaining CO2 concentration of 1250 ppm in the headspace, as aqueous pCO2 may change with biological processes. Six mesocosms were filled with 40L of water from the Chesapeake Bay (three ambient pCO2 and three 1250 ppm) and monitored over 15 days. Chlorophyll a, DOC, bacterial respiration, bacterial production, and enzyme activity were measured. Bacterial production and respiration were used to calculate bacterial growth efficiency (BGE). Results showed that there was no significant difference between the ambient and elevated groups with respect to chlorophyll a, DOC, BGE and enzymes activity. However, differences in bacterial respiration and bacterial production during the first four days of the experiment may suggest that bacteria require time to acclimate to elevated pCO2. Phytoplankton and bacteria in coastal areas are exposed to a wide range of abiotic factors such as seasonal temperature variations, salinity, mixing, and terrestrial inputs. The pH of the Chesapeake Bay ranges between 7.5 and 8.3, and it is possible that the phytoplankton and bacteria are adapted to cope with a wide range of pH (Wong, 2012). This study suggests that the biological carbon pump may not be significantly altered in our future ocean.

Depuis la révolution industrielle, les activités humaines libèrent de grandes quantités de dioxyde de carbone (CO2) dans l'atmosphère. Une partie de cet excès de CO2 est captée par les océans et a provoqué des perturbations et des changements dans le cycle du système carbonaté. Ces perturbations du système carbonaté sont désormais connues pour altérer l'état d'acidification des océans. Dans l'océan Atlantique Sud, les grands tourbillons des Aiguilles, sont parmi les plus grandes structures à méso-échelle des océans. Parce qu'ils sont des structures anticycloniques, ces tourbillons sont associés à des régions où l'océan perd de la chaleur vers l'atmosphère, mais leurs rôles par rapport au système carbonaté sont encore mal connus. Ainsi, l'objectif principal de cette recherche doctorale était d'étudier la relation entre les tourbillons des Aiguilles et la capture et le transport du CO2/Cant tout au long de leur vie ainsi que le rôle que ces structures jouent dans l'état d'acidification de l'océan Atlantique Sud.Lors de cette thèse, nous avons pu démontrer que les tourbillons des Aiguilles sont capables non seulement de capter plus de CO2 que les eaux environnantes, mais aussi de transférer ce carbone en profondeur dans la colonne d'eau et peuvent transporter plus de Cant le long de leur trajectoires. Etant donné que les observations indiquent que 30% de ces structures libérées dans le courant des Aiguilles atteignent la côte ouest de l'océan Atlantique Sud et interagissent même avec le courant du Brésil, nous pouvons les désigner comme l'un des déclencheurs susceptibles d'intensifier l'acidification observée pour les couches centrales de cette région
​Human activities have been releasing large amounts of carbon dioxide (CO2) into the atmosphere since the Industrial Revolution. Part of this excess CO2 is captured by the oceans and has been causing perturbations and changes in the carbonate system cycle. These changes in the carbonate system are now known to alter the acidification state of the oceans.In the South Atlantic Ocean are observed the Agulhas eddies, which are among the largest mesoscale structures in the oceans. Because they are anticyclonic structures, these eddies are associated with regions where the ocean loses heat to the atmosphere, but its role in relation to the carbonate system is still poorly studied. Thus, the main objective of this doctoral research was to investigate the relationship between the Agulhas eddies and CO2/Cant uptake and transport throughout their lives and which role these structures play in the acidification state in the South Atlantic Ocean.As a main conclusion of this thesis, we have been able to demonstrate that the Agulhas eddies are able not only to capture more CO2 than the surrounding waters, but also to transfer into the water column and can carry more Cant along their trajectories. As studies show that 30% of these structures released in the Agulhas leakage reach the west coast of the South Atlantic Ocean and even interact with the Brazilian Current, we can indicate them as one of the triggers that may be intensifying the acidification observed for the central layers of this region
Atividades humanas vêm liberando grandes quantidades de dióxido de carbono (CO 2 ) na atmosfera desde a Revolução Industrial. Parte desse excesso de CO 2 é capturado pelos oceanos (carbono antropogênico, C ant ) e vêm causando perturbações e alterações no ciclo do sistema carbonato. Essas alterações no sistema carbonato alteram o estado de acidificação dos oceanos.No oceano Atlântico Sul observa-se os vórtices das Agulhas, que estão entre as maiores estruturas de mesoescala dos oceanos. Por serem estruturas anticiclônicas, estes vórtices estão associados às regiões em que o oceano perde calor para a atmosfera, porém seu papel em relação ao sistema carbonato ainda é pouco estudado. Dessa forma, o objetivo principal dessa pesquisa de doutorado foi investigar a relação dos vórtices das Agulhas com a captura e transporte de CO 2 /C ant ao longo de suas vidas e qual o papel dessas estruturas no estado de acidificação no oceano Atlântico Sul. Como conclusão principal dessa tese, pudemos demonstrar que os vórtices das Agulhas são capazes não só de capturar mais CO 2 do que as águas ao seu redor, como também de transferir para o interior da coluna d’água, podendo carregar mais C ant ao longo de suas trajetórias. Como estudos mostram que 30% dessas estruturas liberadas no vazamento das Agulhas atingem a costa Oeste do Oceano Atlântico Sul e chegam a interagir com a Corrente do Brasil, podemos indicá-los como um dos gatilhos que podem estar intensificando a acidificação observada para as camadas centrais dessa região

Cette étude a utilisé une approche interdisciplinaire pour évaluer les effets de l'acidification de l'océan sur des ptéropodes et les foraminifères Méditerranéennes. Une comparaison d'échantillons conservés et modernes de 2 espèces de ptéropodes a été réalisée pour étudier les effets du pH sur les propriétés de la coquille. Des populations de ptéropodes ont également été analysées à l'aide des données de séries temporelles. Pour permettre l'amélioration de futures expériences de perturbation, une revue collaborative des techniques de culture de ptéropodes a été produite. Enfin, le foraminifère O. universa a été cultivé dans des conditions de pH et de [CO32-] découplés pour évaluer les effets des changements dans la chimie du carbonate sur la composition en bore et le ?11B. Les coquilles des échantillons conservés de ptéropodes étaient plus épaisses que celles collectées en 2012 et les coquilles de C. inflexa recueillies en 1910 étaient nettement plus denses que celles de 2012, probablement en raison d'un effet de pH. Les abondances de ptéropodes ont montré une tendance croissante entre 1967-2003 et se sont révélées être influencées par les changements de température interannuelles, sans que des changements dans les propriétés des coquilles n'ai eu d'impacts négatifs. Lors de la dernière étude le pH était le seul paramètre du système de carbonate a affecter le ?11Bde la calcite de O. universa. Le B/Ca a diminué avec la diminution du [CO23-] à pH constant mais n'a pas montré de tendance cohérente avec une [CO23-] constant et un pH variable. Au lieu de cela, une étroite corrélation entre les B / Ca et [HCO3-] suggérant que le bore est contrôlé par la [HCO3-]
This study used an interdisciplinary approach to assess the effects of ocean acidification on Mediterranean pteropods and foraminifers. A comparison of museum and modern samples of two pteropod species investigated the effects of pH on shell properties. Pteropod populations were analysed using time series data. To improve future perturbation experiments, a collaborative review of pteropod culture techniques was produced. Finally, the foraminifer O. universa was cultured under decoupled pH and [CO32-] to assess the effects of changes in the carbonate chemistry on boron incorporation and isotope fractionation. Museum pteropod samples were thicker than shells from 2012 and C. inflexa shells collected in 1910 were significantly denser than those from 2012, possibly due to a pH effect. Pteropod abundances displayed an increasing trend between 1967-2003 and are influenced by inter- annual temperature changes, with no sign of the observed changes in shell properties having had negative impacts. pH was the sole parameter of the carbonate system that affected the δ11B of O. universa calcite. The B/Ca ratio decreased with decreasing [CO32-] at constant pH but did not show consistent trends at constant [CO32-] and varying pH. Instead, a close correlation of B/Ca ratios and [HCO3-] was observed suggesting that boron is controlled by the [HCO3-]

Este trabajo se desarrolló en el marco del proyecto Europeo Mediterranean Sea Acidification in a changing climate (MedSeA) (http://medsea-project.eu) con el fin de estudiar los efectos de la limitación por fósforo (P) y el incremento en la presión parcial de dióxido de carbono (pCO2) sobre diferentes aspectos de la biología y ecología de los cocolitóforos. Esta tesis consta de una introducción al tema de estudio donde se presenta el problema de la acidificación oceánica y la limitación por nutrientes en el océano. Se introduce así mismo el organismo de estudio, los cocolitóforos. Los últimos apartados de la introducción contienen los objetivos (expuestos como preguntas de investigación) y una explicación del porqué se eligió el Mar Mediterráneo como zona de estudio. Los siguientes 4 capítulos (capítulos 2 al 5) conforman el “cuerpo del trabajo”. Esta tesis combina diferentes aproximaciones metodológicas, desde experimentos de cultivo y mesocosmos hasta observaciones de campo, para responder preguntas a diferentes escalas, de especies a comunidades. Los capítulos 2 y 3 se basan en experimentos de cultivo realizados con la especie Emiliania huxleyi, la más abundante de las especies de cocolitóforos actuales. Se investigaron los impactos de la limitación por P y la acidificación oceánica en cultivos monoclonales de E. huxleyi. En el Capítulo 2, los posibles impactos de la limitación por P se investigan en 6 cepas de la especie E. huxleyi, 4 de ellas aisladas en el Este del Mediterráneo (ultra-oligotrófico) y 2 en el oeste (oligotrófico a mesotrófico). El Capítulo 3 presenta los resultados de un segundo experimento diseñado para examinar los efectos de la acidificación oceánica en aguas pobres en P sobre una de las cepas de E. huxleyi usadas en el experimento previo. El Capítulo 4 presenta los resultados de dos experimentos de mesocosmos realizados en Córcega y Villefranche-sur-Mer (Francia). Estos se enfocan en cuantificar y entender los impactos de la acidificación oceánica en dos comunidades naturales de coccolitoforos, ambas habitando aguas pobres en P. Finalmente, el Capítulo 5 presenta los resultados del análisis de 81 muestras colectadas entre los 0 – 100 m de profundidad, en diferentes puntos del mar Mediterráneo, incluyendo un transepto de este a oeste (Meteor R.V. campaña M84-3, Abril 2011). Los datos adquiridos proveen una descripción de la distribución de los coccolitoforos durante primavera, lo cual se relacionó con una amplia serie de variables ambientales medidas in situ. Se concluye que la limitación por P amplifica la respuesta a la acidificación oceánica dado que disminuye la densidad celular máxima que los cocolitóforos pueden alcanzar. Juntos, los resultados referentes a la limitación por P (Capítulo 2) y los de otros estudios referentes a la acidificación oceánica (Meyer & Riebesell 2015) sugieren que E. huxleyi puede, en un futuro océano limitado por nutrientes y acidificado, contribuir muy poco a la exportación de carbono inorgánico relativa a la exportación total de materia. Esto favorecería la remineralización en lugar del secuestro a largo tiempo de carbono. Aunque limitación por P no induce malformaciones en los coccolitos de E. huxleyi (Capítulos 2 y 3), bajo una exposición prolongada a una elevada pCO2 y en ausencia de selección entre clones, la acidificación oceánica si causa malformación de los cocolitos irrespectivamente de la [P].
This thesis was conducted in the framework of the European Mediterranean Sea Acidification in a changing climate (MedSeA) project (http://medsea-project.eu). It studies the effects of phosphorus limitation and increased partial pressure of carbon dioxide (pCO2) on different aspects of the biology and ecology of coccolithophores. This thesis starts with an introduction to the studied problem. This is the ocean acidification and phosphorus limitation in the oceans. The organisms under study, the coccolithophores, are also introduced. The last two parts of the introduction expose the objectives of the thesis (exposed as research questions) and an explanation of why the study is performed in the Mediterranean Sea. The following four chapters (chapters 2 to 5) compose the main part of the work. The thesis combines different approaches from culture to mesocosm experiments and field observations, aiming to solve questions at different scale from species to community level. Chapters 2 and 3 are focussing on culture experiments performed on the most abundant modern coccolithophore species, Emiliania huxleyi. The experiments investigate the impacts of phosphorus limitation and ocean acidification on monoclonal E. huxleyi cultures. In Chapter 2 the possible impacts of P limitation are investigated on 6 E. huxleyi clones, 4 of them isolated in the eastern Mediterranean (ultra-oligotrophic) and 2 in the western Mediterranean (oligotrophic to mesotrophic). Chapter 3 presents the results of a second culture experiment designed to test the combined effects of seawater acidification under P limitation in one of the E. huxleyi clones used in the previous experiment. Chapter 4 presents the work performed in two mesocosm experiments conducted off Corsica and Villefrance sur Mer (France). They focussed on the quantification and understating of the impacts of ocean acidification on two different coccolithophore communities inhabiting P poor waters. Finally, Chapter 5 elaborates on field data from 81 samples collected at depths from 0 – 100 m on an east to west transect in the Mediterranean Sea (Meteor Research Vessel, M84-3 cruise, April 2011). The acquired data are used to describe the spring-time coccolithophore distribution in the Mediterranean Sea, which was related to a broad set of in situ measured environmental variables. It is concluded that oligothrophy (i.e. P limitation) amplifies the response to ocean acidification in terms of maximum cell densities. That is, further decreases maximum cell densities. Results on P limitation (Chapter 2) and from other studies in ocean acidification (Meyer & Riebesell 2015) allowed to conclude that E. huxleyi might, in a future P-poor and acidified ocean, contribute relatively little inorganic carbon to exported matter, which would in turn favour remineralization over long term burial at depth. While P limitation does not induce coccolith malformations in E. huxleyi (Chapters 2 and 3), under a long time exposure to enhanced pCO2 and the absence of clone selection, ocean acidification does cause coccolith malformation irrespectively of the [P].

Ocean acidification (OA) refers to the increase in acidity (decrease in pH) of the ocean’s surface waters resulting from oceanic uptake of atmospheric carbon dioxide (CO2). Mounting experimental evidence suggests that OA threatens numerous marine organisms, including reef-building corals; however, few studies have focused on the effects on early life history stages. Coral recruitment is critical to the persistence and resilience of coral reefs and is regulated by several early life processes, including: larval availability (gamete production, fertilization, etc.), larval settlement, post-settlement growth, and survival. Environmental factors that disrupt these early life processes can result in compromised or failed recruitment and profoundly affect future population dynamics. To evaluate the effects of OA on the sexual recruitment of corals, sexual reproduction (including fertilization and sperm swimming speeds) and several critical early life history stages (including larval metabolism, larval settlement, and post-settlement growth) were tested in common Caribbean coral species. Three pCO2 levels were used: ambient seawater (380 µatm) and two pCO2 scenarios that are projected to occur by the middle (560 µatm) and end (800 µatm) of the century as determined by the Intergovermental Panel on Climate Change. Results show that fertilization success, larval metabolic rates, larval settlement rates, and post-settlement growth rates are all compromised with increasing pCO2. This dissertation demonstrates that OA has the potential to negatively impact sexual reproduction and multiple early life history processes of several common Caribbean coral species and may contribute to substantial declines in sexual recruitment that are felt at the community and/or ecosystem scale.

Ocean acidification (OA) presents a fundamental challenge to marine biodiversity and sustained ecosystem health. Reproductive and developmental processes are considered to be particularly vulnerable to OA. My PhD research examined reproductive response (measured as nauplii production), cuticle composition and stage specific growth for the copepod Tisbe battagliai over three generations at four tightly regulated pH conditions (pH 7.67, 7.82, 7.95±0.02; pH 8.l±0.06) and for combined impact ofOA and environmentally relevant copper concentrations. As part of my case studentship with the MBA I also examined OA effects on spermatophore attachment and seminal fluid stores in the female reproductive system. A significantly increased naupliar production at pH 7.95 was attributable to an initial stress response which was succeeded by a hormesis- like response at pH 7.67. The significantly decreased naupliar production at pH 7.82 was the first part of a biphasic reproductive response followed by a compensatory increase in naupliar production at pH 7.67 remaining below control levels. This pattern was consistent across all generations and broods. A mixed effects model predicted a gradual decline in naupliar production over the next 100 years (equivalent to approximately 2,430 generations). Growth (mean length integrated across all developmental stages) decreased significantly below control values at pH 7.82, and 7.67. Cuticle elemental analysis indicated significant alterations in oxygen and carbon content as seawater pH decreased. Changes in growth, cuticle composition and nauplii production strongly suggest that when under OA-induced stress copepods will preferentially reallocate resources in favour of maintaining reproductive output at the expense of somatic growth and cuticle integrity. Experiments incorporating additional copper with increasing OA observed significantly increased naupliar production at pH 8.10, this was followed by a significant reduction in naupliar production beyond that of OA alone from pH 7.95, to pH 7.82, and 7.67. Growth significantly increased with addition of copper, compared to OA impact alone. Cuticle elemental composition observed significant reductions in sulphur, phosphorus and calcium concentrations for those copepods subjected to combined OA and copper. Copepods subjected to additional copper with increasing OA were taking up copper which not only increased metabolism observing a significant increase in growth, but also became toxic observed with a significant further reduction in naupliar production. Addition of copper was seen to have an additive detrimental effect on naupliar production and the copepod population as observed from the mixed effects model output. Techniques developed in . ii. confocallaser scanning microscopy enabled the comparison of seminal fluid stores within the female reproductive system. No significant differences were observed between female reproductive structures and seminal fluid stores with increasing OA from pH 8.1 0 to pH 7.67. Spermatophore size significantly decreased with increasing OA, however to the same extent of female copepod size.

Ocean acidification (OA) is the decrease in ocean pH due to increasing atmospheric pC02• It is predicted that by the year 2100, the pC02 will rise from ca 385 uatm today to 750 uatrn, with a corresponding decrease in surface ocean pH from 8.1 to 7.8. pH was monitored at five stations around a coastal CO2 vent site in Ischia, Italy and the utility of such areas discussed. An ecological survey of benthic macroalgae revealed a substantial community shift at lower pH toward reduced species richness and diversity. The chlorophytes became more dominant at lower pH, with cover increasing from 45-55% at pH 8.16-7.84, to 67-90% at pH 7.48-7.11. Heavily calcified species disappeared at pH 7.48-7.11, but their total cover did not change significantly between pH 8.16-7.80, suggesting some resilience over this century. At lower pH, the DMSP content in macroalgae from Ischia increased in the chlorophytes while in rhodophytes and phaeophytes it decreased. The dark-adapted algal photophysiology suggested a significant benefit when pH was 7.84-7.80, which was lost at pH 7.48-7.11. Two species of common chlorophyte macroalgae VIva lactuca and VIva clathrata, were incubated under pC02 conditions ranging from 432 to 1514 uatrn, In both species, the results indicated that by the year 2100 there could be a large decrease by 50-58% in DMS production, a reduction in chlororespiration, and increased reproductive output in these species. I conclude that increasing pC02 does not directly fertilise photosynthesis or somatic growth in the Ulvales but, reduces chlororespiration, possibly due to carbon-concentrating mechanism down-regulation. This may be the cause of the large reduction in DMS production seen and may lead to a reallocation of resources towards reproductive output. This may increase the prevalence of chlorophyte macroalgae in the future with major repercussions for coastal ecosystems.

Ocean acidification and concurring warming of the oceans poses an ongoing threat to marine organisms, but little is known about their combined effects. The boreal calanoid copepod Calanus finmarchicus is a key stone species in North Atlantic Ocean and adverse effects of concurring OA and warming could have major impacts for ecosystem structure and function. A 2x2 cross factorial experiment with two levels of CO2-concentration (390 (ambient) and 2080ppm (acidified)), and two levels of temperature (11°C (ambient) and 14°C (warming)) were set up to study possible interactive (synergistic/ antagonistic) effects between these two factors. The results show that interactions between the two stressors induced a positive synergistic effect on the development rate (only significant at the C1-stage). Also, a significant reduction in dry weight (1,24 fold) and lipid content (1,56 fold) in animals exposed to warming and acidification combined, suggests that C. finmarchicus could be sensitive towards ocean acidification predicted to occur by year 2300, in combination with increasing temperature. However, acidification also displays an antagonistic effect by reducing the negative effect of warming on the dry weight and lipid content of the animals. The complex interactions induced by combining warming and acidification highlight the importance of looking at multiple environmental factors simultaneously, as this approach might reveal biological responses previously unsuspected.

Trace metal biogeochemistry is projected to be affected by ocean acidification. The understanding of the effects is of particular interest, as trace metals such as Fe and Cu are known for their significant biological roles. Dissolved Fe and Cu in seawater occur predominantly in the form of metal organic complexes. This thesis has investigated the influence that ocean acidification may have on the chemical forms (speciation) of dissolved Fe and Cu in seawater, focusing on their organic complexation, in order to provide a first insight into the possible future changes in their cycling and bioavailability. Competitive Ligand Exchange Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) was used as an analytical technique throughout this PhD work to determine Fe and Cu organic binding ligand characteristics. Organic Fe complexation was determined at current seawater pH in the high latitude North Atlantic (HLNA), which is an area of climate interest due to the importance of iron limitation on phytoplankton productivity and hence the carbon cycle. Main findings indicate that iron biogeochemistry in surface and subsurface waters of the HLNA is controlled by a combination of phytoplankton iron uptake and microbial iron binding ligand production, whilst in deep waters ligand saturation was evident, suggesting that additional Fe would be removed by scavenging or precipitation. The effect of ocean acidification on organic complexation of Fe and Cu was determined in the northwest European shelf seas, during the first UK Ocean Acidification consortium programme research cruise. Results suggested that a decrease in surface ocean pH will potentially result in a reduction of the free and inorganic metal fraction (Fe'), and also in an increase in the organically complexed iron fraction. Direct impacts on Fe bioavailability, however, are difficult to quantify, as the overall iron solubility, and hence its bioavailability, is controlled by the interrelationship between inorganic solubility, organic complexation, redox chemistry, and phytoplankton-trace metal feedback mechanisms. No significant effects were observed of a decrease in pH on the organically complexed Cu (II) fraction, or on the overall free and inorganically bound fraction (Cu'). Consequently, it is not clear so far whether Cu ligand production will be affected by ocean acidification, or the possible effects on its toxicity. In addition, surface water trace metal distribution in the northwest European shelf seas was assessed. Dissolved metal concentrations of Cd, Cu, Fe, Ni and Zn appeared to be significantly influenced by riverine inputs in the study area; whereas surface seawater pH was not evident as a controlling factor. The diversity of the chemical and biological processes controlling Fe and Cu biogeochemistry, and the way in which they will be altered by ocean acidification, is likely to be complex.

La seiche commune, Sepia officinalis, est un céphalopode côtier connu pour ses performances écophysiologiques soutenues par un large répertoire de comportements lui permettant, malgré son cycle de vie court, de tenir un rôle central dans les réseaux trophiques. Cependant, elle est également connue pour accumuler efficacement les éléments métalliques tel que le mercure (Hg), un contaminant neurotoxique sous sa forme organique (methylmercure ; MeHg). De plus, dans le contexte des changements environnementaux globaux, l’acidification des océans (AO) induite par l’augmentation des émissions de CO2, peut impacter le métabolisme, le développement et le système nerveux central, notamment chez les jeunes stades de vie. Le présent travail a donc pour but d’étudier les effets de l’AO sur la bioaccumulation du Hg et les effets de ces deux neurotoxiques (Hg et CO2) sur le comportement et les performances cognitives chez les juvéniles de seiches. Préalablement, des mesures in-situ ont montré que le Hg s’accumulait dans le cerveau des céphalopodes sous forme méthylé (MeHg). Par ailleurs, les approches expérimentales utilisant des traceurs isotopiques (stables et radioactif) du Hg ont démontré que l’accumulation du Hg total provenait majoritairement de l’assimilation du MeHg présent dans les proies, en comparaison à l’accumulation du mercure inorganique (iHg) par voie dissoute. Ce MeHg est ensuite très fortement retenu malgré la mise en évidence de processus de déméthylation du Hg dans la glande digestive. Étonnamment, l’AO n’a aucun effet sur les efficacités de la bioaccumulation et le métabolisme du Hg. En termes d’effets, des essais comportementaux ont montré que le Hg et CO2, seuls ou combinés, n’impactaient pas l’acuité visuelle et les performances de prédation chez les juvéniles. Par contre, ces deux derniers induisent une augmentation de l’activité locomotrice, compromettant le comportement défensif à travers notamment une altération de la coloration disruptive et un non-alignement de la latéralisation. Parmi les processus neuronaux susceptibles d’être impactés par le Hg et le CO2, le système GABAergique a été analysé dans les lobes optiques mais n’a montré aucun lien évident avec les réponses comportementales suggérant des processus d’effets plus complexes. L’ensemble de ce travail questionne donc les effets des conditions futures de l’océan sur les juvéniles de seiches, et plus largement les impacts sur les populations de céphalopodes
The common cuttlefish, Sepia officinalis, is a coastal cephalopod known for its eco physiological performance supported by a wide repertoire of behaviors that allows it, despite its short life cycle, to play a central role in food webs. However, it is also known to efficiently accumulate metallic elements such as mercury (Hg), a neurotoxic contaminant in its organic form (methylmercury; MeHg). Moreover, in the context of global changes, ocean acidification (OA) induced by the increase of CO2 emissions, can impact metabolism, development and the central nervous system, especially in young life stages. The present work therefore aims to study the effects of OA on Hg bioaccumulation and the effects of these two neurotoxicants (Hg and CO2) on behavior and cognitive performance in juvenile cuttlefish. In the first place, in-situ measurements showed that Hg accumulated in the brain of cephalopods in methylated form (MeHg). Moreover, experimental approaches using isotopic tracers (stable and radioactive) of Hg have shown that the accumulation of total Hg comes mainly from the assimilation of MeHg present in preys, compared to the accumulation of inorganic mercury (iHg) dissolved in seawater. This MeHg is then very strongly retained despite evidence of Hg demethylation processes in the digestive gland. Surprisingly, OA has no effect on the bioaccumulation efficiencies and metabolism of Hg. In terms of effect, behavioral assays showed that Hg and CO2, alone or in combination, did not impact visual acuity and predation performance in juveniles. However, both induced an increase in locomotor activity, compromised defensive behavior through, in particular, an alteration of disruptive coloration and a non-alignment of lateralization. Among the neural processes likely to be impacted by Hg and CO2, the GABAergic system was analyzed in the optic lobes but showed no obvious link with behavioral responses suggesting more complex effect processes. All of this work therefore questions the effects of future ocean conditions on juvenile’s cuttlefish, and more broadly the impacts on cephalopod populations

Le plancton a un rôle crucial dans le cycle du carbone. Il est donc primordial de projeter son évolution dans le contexte de changement climatique. Une partie des résultats rapportés au niveau des communautés planctoniques montrent une stimulation de la production primaire avec l’augmentation de concentration en CO2 et très peu d’expériences combinant plusieurs facteurs ont été faites. Qui plus est, les expériences ont été réalisées majoritairement dans des conditions naturellement élevées ou enrichies en sels nutritifs et très peu de données existent dans les zones naturellement pauvres en nutriments et chlorophylle a, c’est à dire dans les zones oligotrophes telles que la mer Méditerranée, bien que ces régions représentent une surface importante et en expansion de la surface de l’océan. Plusieurs approches ont été utilisées au cours de cette thèse pour étudier les effets du réchauffement et de l’acidification de l’océan sur des communautés planctoniques dans le NO de la Méditerranée. Une des approches, restreinte à l’effet de l’acidification seule, a été l’utilisation de mesocosmes. En Baie de Calvi (expérience #1; été 2012 sur 22 jours) la communauté étudiée présentait un efficace processus de recyclage des sels nutritifs ainsi qu’une production régénérée importante alors que dans le Baie de Villefranche (expérience #2; hiver/printemps 2013 durant 11 jours) la communauté était caractérisée plutôt par un système autotrophe et par une production nouvelle dominante. Une troisième expérience a été réalisée pour étudier les effets synergétiques de l’acidification et du réchauffement de l’océan (expérience #3; March 2012; post-bloom). Toutes les expériences ont ainsi été menées dans des conditions de faibles concentrations en sels nutritifs avec des communautés dominées par des petites espèces phytoplanctoniques telles que des haptophytes, cynaobacteries et chlorophytes. Lors de l’expérience #3, toutes les populations ont décliné au cours de l’expérience (12 jours) à l’exception des cyanobactéries (principalement Synechococcus spp.) qui ont significativement augmenté durant cette période. Cette augmentation était d’autant plus prononcée dans les conditions de température plus élevée, bien que l’augmentation concomitante de CO2 ai eu tendance à limiter cet effet. Pour les trois expériences, l’acidification de l’océan seule n’a pas montré d’effet sur les taux métaboliques quelque soit la méthode utilisée (O2-LD, marquage au 18O, 13C et 14C) alors que durant l’expérience #3, les conditions élevées en température ont favorisé la production brute déterminée par la méthode de marquage 18O. Des biomarqueurs spécifiques, les acides gras des lipides polaires, utilisés de façon combinée avec du marquage au 13C a permis la détermination des productions primaires par groupe. Ceci a confirmé que l’acidification de l’océan seule n’a pas particuliérement favorisé un groupe phytoplanctonique par rapport à un autre dans nos conditions expérimentales.Basé sur nos résultats et sur une revue de littérature, il apparait que la plupart des expériences (57 % des études) réalisées jusqu’à maintenant n’ont pas montré d’influence notoire de l’acidification de l’océan seule sur les communautés planctoniques, alors que le réchauffement de l’océan semble avoir plus d’effet sur la composition et la production planctonique. De plus, la biomasse dans les écosystèmes dominés par des petites espèces de phytoplancton semble être insensible à l’augmentation de CO2. A l’heure actuelle, il est impossible, basé sur ces résultats, de fournir un concept général de l’effet de l’acidification de l’océan sur les communautés planctoniques. Cependant il semble que l’acidification n’augmentera pas la biomasse et la production primaire pour la majorité des communautés
Plankton plays a key role in the global carbon cycle. It is therefore important to projectthe evolution of plankton community structure and function in a future high-CO2 world.Several experimental results reported at the community level have shown increased rates ofprimary production as a function of increasing pCO2 and few multi-driver experiments havebeen performed. However, the great majority of these experiments have been performedunder high natural or nutrient-enriched conditions and very few data are available in areaswith naturally low levels of nutrient and chlorophyll i.e. oligotrophic areas such as theMediterranean Sea, although they represent a large and expanding part of the ocean surface.Several approaches have been used during this thesis to investigate the effects ofocean warming and acidification on plankton communities in the NW Mediterranean Sea.One approach, restricted to the investigation of ocean acidification effects alone, was the useof mesocosms. In the Bay of Calvi (experiment #1; summer 2012 during 22 days), thecommunity was very efficient in recycling nutrients and showed important regeneratedproduction while in the Bay of Villefranche (experiment #2; winter/spring 2013 during 11days) the community was characterized by a more autotrophic state and larger newproduction. A third experiment was set-up to investigate the combined effects of oceanacidification and warming in small containers in the Bay of Villefranche (experiment #3;March 2012; post-bloom conditions).All experiments were conducted under low nutrient conditions with communitiesdominated by small species (e.g. haptophytes, cyanobacteria, chlorophytes). During the thirdexperiment, biomass of populations decreased throughout the experiment (12 days), exceptcyanobacteria (mostly Synechococcus spp.) that significantly increased during that period.This increase was even more pronounced under elevated temperature, albeit the combinationwith elevated pCO2 tended to limit this effect. For the three experiments, ocean acidificationalone had no effect on any of the metabolic processes, irrespective of the methods used (O2-LD, as well as 18O, 13C and 14C labelling) while during the multi-driver experiment #3, oceanwarming led to enhanced gross primary production as measured by the 18O labellingtechnique. Specific biomarkers, polar lipid fatty acids, were used in combination with 13Clabelling to assess group primary production rates. This confirmed that ocean acidificationalone did not favour any phytoplankton group under our experimental conditions.Based on our findings and on an extensive literature review, it appears that most (57%) of the experiments performed to date have shown no effect of ocean acidification alonewhile ocean warming seem to have an effect on plankton composition and production.Furthermore, plankton biomass in ecosystems dominated by small phytoplankton speciesappears insensitive to elevated CO2. It remains, for the moment, impossible based on thesefindings to provide a general concept on the effect of ocean acidification on planktoncommunities. However, it appears that ocean acidification will likely not lead to increasedbiomass and primary production rates for most communities, as it was previously anticipated.Furthermore, although warming will likely lead to increased primary production, it appearsthat small species with a low capacity for export will be favoured. If this proves to be awidespread response, plankton will not help mitigating atmospheric CO2 increase through anenhancement of the biological pump

Le plancton a un rôle crucial dans le cycle du carbone. Il est donc primordial de projeter son évolution dans le contexte de changement climatique. Une partie des résultats rapportés au niveau des communautés planctoniques montrent une stimulation de la production primaire avec l’augmentation de concentration en CO2 et très peu d’expériences combinant plusieurs facteurs ont été faites. Qui plus est, les expériences ont été réalisées majoritairement dans des conditions naturellement élevées ou enrichies en sels nutritifs et très peu de données existent dans les zones naturellement pauvres en nutriments et chlorophylle a, c’est à dire dans les zones oligotrophes telles que la mer Méditerranée, bien que ces régions représentent une surface importante et en expansion de la surface de l’océan. Plusieurs approches ont été utilisées au cours de cette thèse pour étudier les effets du réchauffement et de l’acidification de l’océan sur des communautés planctoniques dans le NO de la Méditerranée. Une des approches, restreinte à l’effet de l’acidification seule, a été l’utilisation de mesocosmes. En Baie de Calvi (expérience #1; été 2012 sur 22 jours) la communauté étudiée présentait un efficace processus de recyclage des sels nutritifs ainsi qu’une production régénérée importante alors que dans le Baie de Villefranche (expérience #2; hiver/printemps 2013 durant 11 jours) la communauté était caractérisée plutôt par un système autotrophe et par une production nouvelle dominante. Une troisième expérience a été réalisée pour étudier les effets synergétiques de l’acidification et du réchauffement de l’océan (expérience #3; March 2012; post-bloom). Toutes les expériences ont ainsi été menées dans des conditions de faibles concentrations en sels nutritifs avec des communautés dominées par des petites espèces phytoplanctoniques telles que des haptophytes, cynaobacteries et chlorophytes. Lors de l’expérience #3, toutes les populations ont décliné au cours de l’expérience (12 jours) à l’exception des cyanobactéries (principalement Synechococcus spp.) qui ont significativement augmenté durant cette période. Cette augmentation était d’autant plus prononcée dans les conditions de température plus élevée, bien que l’augmentation concomitante de CO2 ai eu tendance à limiter cet effet. Pour les trois expériences, l’acidification de l’océan seule n’a pas montré d’effet sur les taux métaboliques quelque soit la méthode utilisée (O2-LD, marquage au 18O, 13C et 14C) alors que durant l’expérience #3, les conditions élevées en température ont favorisé la production brute déterminée par la méthode de marquage 18O. Des biomarqueurs spécifiques, les acides gras des lipides polaires, utilisés de façon combinée avec du marquage au 13C a permis la détermination des productions primaires par groupe. Ceci a confirmé que l’acidification de l’océan seule n’a pas particuliérement favorisé un groupe phytoplanctonique par rapport à un autre dans nos conditions expérimentales.Basé sur nos résultats et sur une revue de littérature, il apparait que la plupart des expériences (57 % des études) réalisées jusqu’à maintenant n’ont pas montré d’influence notoire de l’acidification de l’océan seule sur les communautés planctoniques, alors que le réchauffement de l’océan semble avoir plus d’effet sur la composition et la production planctonique. De plus, la biomasse dans les écosystèmes dominés par des petites espèces de phytoplancton semble être insensible à l’augmentation de CO2. A l’heure actuelle, il est impossible, basé sur ces résultats, de fournir un concept général de l’effet de l’acidification de l’océan sur les communautés planctoniques. Cependant il semble que l’acidification n’augmentera pas la biomasse et la production primaire pour la majorité des communautés
Plankton plays a key role in the global carbon cycle. It is therefore important to projectthe evolution of plankton community structure and function in a future high-CO2 world.Several experimental results reported at the community level have shown increased rates ofprimary production as a function of increasing pCO2 and few multi-driver experiments havebeen performed. However, the great majority of these experiments have been performedunder high natural or nutrient-enriched conditions and very few data are available in areaswith naturally low levels of nutrient and chlorophyll i.e. oligotrophic areas such as theMediterranean Sea, although they represent a large and expanding part of the ocean surface.Several approaches have been used during this thesis to investigate the effects ofocean warming and acidification on plankton communities in the NW Mediterranean Sea.One approach, restricted to the investigation of ocean acidification effects alone, was the useof mesocosms. In the Bay of Calvi (experiment #1; summer 2012 during 22 days), thecommunity was very efficient in recycling nutrients and showed important regeneratedproduction while in the Bay of Villefranche (experiment #2; winter/spring 2013 during 11days) the community was characterized by a more autotrophic state and larger newproduction. A third experiment was set-up to investigate the combined effects of oceanacidification and warming in small containers in the Bay of Villefranche (experiment #3;March 2012; post-bloom conditions).All experiments were conducted under low nutrient conditions with communitiesdominated by small species (e.g. haptophytes, cyanobacteria, chlorophytes). During the thirdexperiment, biomass of populations decreased throughout the experiment (12 days), exceptcyanobacteria (mostly Synechococcus spp.) that significantly increased during that period.This increase was even more pronounced under elevated temperature, albeit the combinationwith elevated pCO2 tended to limit this effect. For the three experiments, ocean acidificationalone had no effect on any of the metabolic processes, irrespective of the methods used (O2-LD, as well as 18O, 13C and 14C labelling) while during the multi-driver experiment #3, oceanwarming led to enhanced gross primary production as measured by the 18O labellingtechnique. Specific biomarkers, polar lipid fatty acids, were used in combination with 13Clabelling to assess group primary production rates. This confirmed that ocean acidificationalone did not favour any phytoplankton group under our experimental conditions.Based on our findings and on an extensive literature review, it appears that most (57%) of the experiments performed to date have shown no effect of ocean acidification alonewhile ocean warming seem to have an effect on plankton composition and production.Furthermore, plankton biomass in ecosystems dominated by small phytoplankton speciesappears insensitive to elevated CO2. It remains, for the moment, impossible based on thesefindings to provide a general concept on the effect of ocean acidification on planktoncommunities. However, it appears that ocean acidification will likely not lead to increasedbiomass and primary production rates for most communities, as it was previously anticipated.Furthermore, although warming will likely lead to increased primary production, it appearsthat small species with a low capacity for export will be favoured. If this proves to be awidespread response, plankton will not help mitigating atmospheric CO2 increase through anenhancement of the biological pump