Dissertations / Theses on the topic 'Larval metamorphosis'

Le maintien et le renouvellement des populations de poissons coralliens dépendent en grande partie du recrutement larvaire, c’est-à-dire de l’installation des larves pélagiques dans les habitats récifaux adultes, et de leur survie après s’être métamorphosées en juvéniles. De plus en plus d’études révèlent que les changements de composition de l’eau, causés par le changement climatique et la pollution, peuvent altérer les capacités sensorielles des poissons coralliens, diminuant leurs aptitudes à localiser des habitats propices (maximisant leur croissance et diminuant leur mortalité) lors de l’installation. Cependant, les mécanismes internes à l’origine de ces phénomènes sont méconnus. Lors de cette thèse, j’ai examiné le recrutement larvaire du poisson chirurgien bagnard Acanthurus triostegus et mis en évidence que les changements écologiques, morphologiques, physiologiques et comportementaux qui s’y déroulent correspondent à une métamorphose contrôlée par les hormones thyroïdiennes (HT). J’ai ensuite analysé comment des stress d’origine anthropique, tels que l’élévation des températures de surface et la pollution par un pesticide d’origine agricole, peuvent perturber sa métamorphose. Lors de cette étape clé de leur cycle de vie, ces perturbations diminuent les taux d’HT, altérant la maturation de leurs organes sensoriels, leurs capacités sensorielles, et augmentant leur mortalité. Cette thèse est donc une analyse holistique de l’impact des perturbations anthropiques sur les processus moléculaires, et les changements histologiques, anatomiques et comportementaux du recrutement larvaire des poissons coralliens. Elle souligne l’importance du système thyroïdien, et invite à une meilleure compréhension des processus endocriniens du recrutement larvaire, dans l’optique d’une amélioration de la conservation des récifs coralliens
The persistence and sustainability of coral-reef fish populations depends on the continued larval recruitment, i.e. successful settlement by pelagic larvae into adult reef habitats and post-settlement survival through metamorphosis to a juvenile stage. There is growing evidence that changes to water conditions due to global change and waterborne pollution can impair coral-reef fish sensory abilities to locate settlement habitats that maximize growth while minimizing mortality risk. However, the inner mechanisms of such impairments remain unknown. In this thesis, I have examined the recruitment phase of the convict surgeonfish Acanthurus triostegus, and determined that the ecological, morphological, physiological and behavioral changes occurring at recruitment correspond to a metamorphosis mediated by thyroid hormones (TH). Then, I investigated whether this metamorphosis is prone to endocrine disruption under anthropogenic disturbances such as elevated sea water temperature and agricultural pesticide pollution. I demonstrated that such pressures can reduce TH levels at a critical developmental stage in coral-reef fishes, impairing their metamorphic processes such as intestine remodeling, sensory organ maturation, and sensory abilities acquisition, further increasing their mortality rates. Overall, this thesis is a holistic analysis that addresses molecular, histological, anatomical, and behavioral assays of multiple stressors affecting coral-reef fish recruitment. It indicates the importance of a proper endocrine function during coral-reef fish recruitment, highlighting the need for a better understanding of these processes for coral-reef conservation

Thesis (Ph. D.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Cell Biology & Molecular Genetics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The ability of animals to vary growth, development rate and behaviour in response to environmental conditions has been well documented, particularly during the larval phase in animals with complex life cycles. The evolution and maintenance of plasticity in response to environmental conditions is likely to be adaptive in animals that face unpredictable environments. However, there are two aspects of life histories in animals with complex life cycles, which would be expected to favour plasticity, that have received limited attention: traits during metamorphic climax and variation in the life history phase at which temperate species spend the winter. Therefore the aims of this thesis were to consider the environmental factors that are likely to result in plasticity in the timing and duration of metamorphic climax and contribute to variation in the over-wintering life stage, using amphibians as study animals. To assess the ability of animals to respond to environmental conditions during metamorphic climax conditions were manipulated during metamorphosis independent of larval treatment. Accordingly all larvae entered metamorphic climax having experienced the same conditions. The African clawed toad, Xenopus laevis, was used. I examined the influence of environmental temperature, predation risk and starting body size on several traits during the transitional stage (e.g. mass, snout-vent length (SVL), head width, tail morphology, duration and locomotor performance). Morphological measures and the duration of the life stage were shown to vary with temperature and predation risk. As predicted, higher temperatures and the risk of predation resulted in faster development through metamorphosis and smaller sizes on completion. The acceleration of metamorphosis was demonstrated to have potential costs, not in the form of reduced locomotor performance as predicted, but in a reduction in juvenile size as a result of faster metamorphic development. This suggests that, during this potentially vulnerable stage, it would be advantageous to take more time to complete in the absence of predators. Greater body size at the onset of metamorphosis requires a longer time to complete metamorphic climax suggesting that having a greater quantity of tissue to reconfigure during metamorphosis takes more time. Therefore, the conditions experienced during metamorphosis may have important implications for juvenile fitness and should be considered in studies of life history plasticity. In many temperate species with complex life cycles, the life history stage at which a species can survive the winter is generally fixed, imposing time limits on the timing of development. Most of these species must therefore often modify developmental rate to reach the appropriate stage or size at the onset of winter, usually at a cost to other traits. However, variation in the stage or developmental group that some amphibian, fish and insect species spend the winter has been observed, such as in the common frog Rana temporaria in the UK, which can spend the first winter as either a tadpole or as a juvenile frog. To investigate the factors that contribute to this variation in life history, I examined the influence of environmental temperature, food availability and water depth on the rate of larval development and growth. Data on development, growth and environmental temperature of a field population of R. temporaria, which have been observed to over-winter as larvae, were collected to determine how and when the two divergent early life history patterns of development were established. Development rate was slowed by reduced temperatures and food availability and greater water depth during rearing. Temperature and food availability also had a significant impact on the proportion of larvae that over-wintered, but in the field other factors are likely to contribute to the within-population variation in wintering strategy. While a greater water depth did prolong larval development, as predicted, this does not appear to be due to the cost of surfacing to respire acting as a constraint on development, since a similar slowing in development was observed in the lung-less Bufo bufo tadpoles. The results of these studies did not allow a definitive assessment of whether over-wintering as larvae represents an adaptive strategy or occurs as the result of developmental constraints. There is some evidence that over-wintering as larvae might be adaptive, since on completion of metamorphosis individuals that wintered as larvae were larger than those that completed metamorphosis late in the summer. Further work is necessary to identify other factors contributing to the over-wintering of larvae in Rana temporaria and to determine the adaptive significance, if any, of the alternative life history patterns.

Ambystoma tigrinum undergoes an obligatory metamorphosis while A. mexicanum fails to metamorphose and exhibits paedomorphosis. While it is clear that salamander paedomorphosis is associated with genetic changes that delay developmental timing, it is not clear when and how these changes manifest during development. It is possible that paedomorphic and metamorphic larvae show equivalent patterns of developmental until late in the larval period, when brain regions become competent to stimulate the release of metamorphic hormones. To test this hypothesis, I compared gene expression patterns between the brains of A. mexicanum and A. t. tigrinum larvae. In support of the developmental equivalence hypothesis, 114 differentially expressed genes (DEGs) were identified in common between the species and all but 2 showed the same temporal pattern of expression. However, more DEGs were identified uniquely from each species. In particular, several genes that are associated with the hypothalamus-pituitaryinterrenal axis, which is implicated in metamorphic regulation in amphibians, exhibited significant expression differences between A. mexicanum and A. t. tigrinum larvae. The results show that metamorphic and paedomorphic modes of development are associated with different transcriptional programs in the brain and these programs diverge during early larval development.

This study investigated the reproduction, larval growth and metamorphosis of the nudibranchs Onchidoris bilamellata (L.) and Goniodoris nodosa (Montagu) under controlled laboratory conditions. In addition, the rare occurrence of spawning events of O. bilamellata taking place in the field outwith the winter and spring reproductive period was studied. Onchidoris bilamellata and Goniodoris nodosa differ in the size and number of eggs produced per spawning event. In the present study O. bilamellata does not exhibit a clear spawning pattern, whereas G. nodosa lays increasingly smaller eggs and larvae as the season progresses. The diameter of the eggs of O. bilamellata is not correlated with the organic content per egg. The data available for G. nodosa were insufficient to analyse this relationship. The rates of larval growth and development are reported for Onchidoris bilamellata and Goniodoris nodosa. These variables do not differ significantly for O. bilamellata between cultures maintained under various light regimes, ranging from continuous darkness to continuous illumination, and are comparable to those of G. nodosa. The shell growth pattern exhibited by larvae of G. nodosa is sigmoid, similar to that of other opisthobranchs. Spawn masses laid during the winter and spring months were collected fresh from the field and compared to spawn masses collected from the field in July and September, outwith the typical spawning period of Onchidoris bilamellata in the British Isles. The shell size of the July and September hatchlings was significantly smaller than that of the winter and spring hatchlings. Furthermore, the larvae hatched from spawn masses laid in September cultured in the laboratory exhibited high mortality rates and the overwhelming majority did not survive through metamorphosis. The significance of the spawning activity of O. bilamellata past the typical spawning period of this species is discussed. The induction of metamorphosis of Onchidoris bilamellata was investigated using seawater containing elevated concentrations of potassium ion, and the results indicate that the optimal concentration inductive of metamorphosis is 19 mM K+ ASW, Metamorphosis experiments were also performed with the natural prey of O. bilamellata, the acorn barnacle Semibalanus balanoides (L.). The results suggest that pediveligers can be induced to metamorphose at a distance from the inductive substrata. Attempts were made to identify the natural inductive cue of Goniodoris nodosa, but this was not successful.

The global stressors of ocean warming and acidification, as well as local stressors such as eutrophication, overfishing, and coastal construction, have all contributed to the severe decline in coral populations worldwide. Recovery of coral reefs depends partly on recruitment, which relies on the response of larvae to settlement cues indicative of habitat quality; however, it remains unclear whether recruitment in disturbed areas will be compromised. Specifically, as reefs become more disturbed and dominated by macroalgae, it is important to understand larval behavior in response to changes in habitat quality. In this study, we first assessed the settlement success of newly released Agaricia agariciteslarvae in response to several settlement cues, including temperature and water movement. Then, to test the Desperate Larva Hypothesis, the ability of larvae of different ages (0-7 days) to settle and discriminate between inducing and inhibitory settlement cues was assessed. Newly released larvae displayed a stronger preference for settling on crustose coralline algae (93%) than on ceramic plates in macroalgae- (30%) or conspecific-treated seawater (5%), or filtered seawater (13%) (control). Older larvae became progressively less discriminatory of settlement cues, settling even in response to inhibitory cues. This confirms that, although the absence of good settlement cues initially deters settlement, larvae become desperate as they become older and settle even on unfavorable substrates, thus contributing to recruitment in poor quality habitats.

Significant seasonal variation in size at settlement has been observed in newly settled larvae of Dreissena polymorpha in Lake Constance. Diet quality, which varies temporally and spatially in freshwater habitats, has been suggested as a significant factor influencing life history and development of freshwater invertebrates. Accordingly, experiments were conducted with field-collected larvae to test the hypothesis that diet quality can determine planktonic larval growth rates, size at settlement and subsequent post-metamorphic growth rates. Larvae were fed one of two diets or starved. One diet was composed of cyanobacterial cells which are deficient in polyunsaturated fatty acids (PUFAs), and the other was a mixed diet rich in PUFAs. Freshly metamorphosed animals from the starvation treatment had a carbon content per individual 70% lower than that of larvae fed the mixed diet. This apparent exhaustion of larval internal reserves resulted in a 50% reduction of the postmetamorphic growth rates. Growth was also reduced in animals previously fed the cyanobacterial diet. Hence, low food quantity or low food quality during the larval stage of D. polymorpha lead to irreversible effects for postmetamorphic animals, and is related to inferior competitive abilities.

Made available in DSpace on 2016-06-02T18:55:29Z (GMT). No. of bitstreams: 1 6442.pdf: 2821557 bytes, checksum: fa6229cde894643bd94017a2424cf314 (MD5) Previous issue date: 2014-12-05
Financiadora de Estudos e Projetos
Africanized Apis mellifera bees Linnaeus, 1758 (Hymenoptera: Apidae), although not native to Brazil, is very important both for the environment and for the economy. However, with the growth of food production and biofuels, there was an expansion of the areas of monoculture consequently was increased also the use of fertilizers and pesticides. Although some insecticides such a fipronil (used in sugar cane) and dimethoate (standard substance in larval tests standardized by the Organization for Economic Cooperation and Development and used in cotton crops), are toxic to bees. Thus the present study aimed to evaluate the biological and histological effects of toxicity of pesticides in the ontogenetic development of Africanized A. mellifera. For this, worker larvae of 1st instar were collected from healthy colonies of the apiary located in the rural town of Piedade/SP and transferred to sterile polystyrene cells, which contained larval diet. After the transfer, the cells were maintained at a temperature of 34±2° C and RH 85±5%, the larvae fed daily from 1st to 5th day. On day 4, were prepared with three different concentrations (20, 5 and 0.5 ng a.i./μL) fipronil and dimethoate a concentration (200 ng a.i./μL) was added 1 μL of each concentration prepared (isolated) under integument of the larva, called acute treatment. The results showed that there was no larval mortality (72 hours) significantly between groups (p>0.20), exposed to fipronil and control, but the pupae rate anomalous (p<0.03) and emergency (p<0.04) was found significant difference. The most common abnormalities were pigmentation on the upper and lower body, head and malformation in the absence of members; pink eye pupa (Pp) and white eyed pupae (Pw) with malformation of the limbs, having formed the eye and with larval body. It is assumed that the fipronil be a neurotoxic compound, he is acting in the regulation and release of Ecdysteroid hormones that are involved in the passage from larva to adult (metamorphic process). After the bioassay dimethoate, pre-pupae were collected (D9) for morphological and histochemical analysis for both treatment groups and for the control. Pre-pupae were processed routinely. Histological sections were stained with Hematoxylin-Eosin. For immunohistochemical analysis, we used the Bromophenol Blue reactions, Periodic Acid-Schiff and Feulgen. By morphological and histochemical analysis, changes were observed in muscle tissue, intracellular spacing of trophocytes and oenocytes, increase in the amount of proteins and lipids and nuclear branch in trophocytes. Most of these characteristics are described pupae, however individuals were analyzed in the pre-pupae stage, namely, and it is likely that the substance studied on the development of bees exposed to the insecticide. Dimethoate could activate the cellular detoxification system by carboxylesterases enzymes and, in this way, cause the hydrolysis of the Juvenile Hormone and hence the acceleration of the metamorphic layers. The high rate of abnormalities in the pupal stage and decreased emergency rate in individuals exposed to fipronil raises concerns with decreasing productivity in commercial apiaries located in agro-ecosystems. In addition, the advance from the present study calls attention to damage in the colony, as in nature the metamorphosis of the phases have certain duration. This can cause physiological disorder could indirectly damage the chain pollination by bees.
A abelha Apis mellifera africanizada Linnaeus, 1758 (Hymenoptera: Apidae), apesar de não ser nativa do Brasil, é muito importante tanto para o ambiente quanto para a economia. Porém, com o crescimento da produção de alimento e biocombustíveis, houve uma expansão das áreas de monocultura, consequentemente aumentou-se também o uso de fertilizantes e de defensivos agrícolas. Entretanto, alguns inseticidas, como o fipronil (utilizado em cana-de-açúcar) e o dimetoato (substância padrão em testes larvais padronizados pela Organização para a Cooperação e Desenvolvimento Econômico e utilizado em culturas de algodão), são tóxicos para as abelhas. Diante disso o presente estudo teve como objetivo geral avaliar os efeitos biológicos e histológicos da toxicidade desses defensivos agrícolas no desenvolvimento ontogenético de A. mellifera africanizada. Para isso, larvas de operárias de 1º ínstar foram coletadas de colônias saudáveis do apiário localizado na zona rural da cidade de Piedade/SP e foram transferidas para cúpulas de poliestireno esterilizadas, as quais continham dieta larval. Após a transferência, as cúpulas foram mantidas à temperatura de 34±2º C e UR de 85±5º %, sendo as larvas alimentadas diariamente do 1º ao 5º dia. No 4º dia, prepararam-se três concentrações (20, 5 e 0.5 ng i.a./μL) de fipronil e para o dimetoato uma concentração (200 ng i.a./μL).. Foi adicionado 1 μL de cada concentração preparada (isolado) sob o tegumento da larva, chamado tratamento agudo. Os resultados evidenciaram que não houve mortalidade larval (72 horas) significativa entre os grupos (p>0.20) expostos com fipronil e o controle, porém na taxa de pupas anômalas (p<0.03) e de emergência (p<0.04) constatou-se diferença significativa. As anomalias mais comuns foram: pigmentação na parte superior e inferior do corpo, malformação na cabeça e ausência de membros; pupa de olho rosa (Pp) e pupa de olho branco (Pw) com malformação dos membros, tendo formado o olho e ainda com corpo larval. Supõe-se que pelo fipronil ser um composto neurotóxico, ele esteja agindo na regulação e liberação dos hormônios ecdisteróides que estão envolvidos na passagem de larva a adulto (processo metamórfico). Após o bioensaio com o dimetoato, foram coletadas pré-pupas (D9) para as análises morfológicas e histoquímica, tanto para os grupos expostos como para o controle. Pré-pupas foram processadas rotineiramente. As secções histológicas foram coradas com Hematoxilina-Eosina. Para a análise histoquímica utilizou-se as reações de Azul de Bromofenol, Ácido Periódico de Schiff e Feulgen. Através da análise morfológica e histoquímica, foram observadas alterações no tecido muscular, espaçamentos intracelular de trofócitos e enócitos, aumento na quantidade de proteínas e lipídios e ramificação nuclear nos trofócitos. A maioria dessas características descritas é de pupas, porém os indivíduos analisados estavam na fase de pré-pupa, ou seja, é provável que a substância estudada adiante o desenvolvimento das abelhas expostas ao inseticida. O dimetoato poderia ativar o sistema de desintoxicação celular pelas enzimas carboxilesterases e, por essa via, ocasionar a hidrólise do Hormônio Juvenil e, consequentemente, a aceleração das fases metamórficas. A alta taxa de anomalias na fase pupal e a diminuição da taxa de emergência em indivíduos expostos ao fipronil aumenta a preocupação com a diminuição da produtividade nos apiários comerciais localizados nos agro-ecossistemas. Além disso, o adiantamento encontrado no presente trabalho chama atenção para danos na colônia, já que na natureza as fases da metamorfose têm uma determinada duração. Esse possível distúrbio fisiológico poderia causar de forma indireta prejuízos na cadeia da polinização realizada pelas abelhas.

This thesis focussed on the effects of a range of trace metals on various stages of Haliotis rubra development. The trace metals assessed in this thesis were the essential metals Cu, Zn and Fe; and, the non-essential metals Hg, Cd and Pb. Copper and Hg proved to be the two most toxic metals to the life stages of H. rubra studied. The concentrations affecting normal development of the fertilised egg exposed for 48h showed a decreasing order of toxicity with 48hEC50 recorded at 7µg Cu/L, 20µg Hg/L, 42µg Zn/L, 4,102µg Fe/L, 4,515µg Cd/L, and 5,111µg Pb/L. Settlement and metamorphosis occur in normal larvae when aged 5 days, and exposure of the 5 day old larvae to the metals for 48h resulted in impaired crawling success at 128µg/L Cu and Hg, and 1250µg Cd/L. Settlement was inhibited after exposure to 128µg Cu/L, 32µg Hg/L, and 1250 Cd/L. Metamorphosis of larvae 96h after exposure was inhibited by 32µg Cu/L, 512µg Zn/L, 32µg Hg/L and 625µg Cd/L. The rate of meta morphosis was enhanced after exposure to Cu and Hg at 0.5µg/L and 64 - 256µg Zn/L. Exposure to Zn at concentrations 64, 128 and 256 µg Zn/L caused an increased rate of settlement and metamorphosis. Juvenile H. rubra exposed to the six metals for 96h were most sensitive to Cu, which produced a 96hLC50 of 87µg Cu/L compared to Hg with a 96hLC50 of 173µg Hg/L. Juvenile H. rubra were relatively insensitive to Zn and Cd with the 96h LC50 of 1730µg Zn/L and 3700µg Cd/L, respectively. Exposure to individual solutions of Cu, Zn, and Cd for 28 days resulted in juvenile H. rubra bioaccumulating significant concentrations of metals in the visceramantleedible foot muscle. Accumulation of Hg was greater in the mantle-viscera-edible foot muscle. Following exposure, depuration in clean seawater for 28 days produced varying decreases in metal concentrations for each tissue compartment. Sodium-potassium activated ATPase (Na+,K+-ATPase) activity in the gills of juvenile H. rubra was significantly affected following expos ure to the trace metals for 28 days, with a decreasing order of effect on enzyme activity of Hg-Cu-Cd-Zn. Depuration of H. rubra in clean seawater for 28 days resulted in the recovery of Na+,K+-ATPase activity to varying degrees. The recovery of ATPase activity was more efficient following exposure to Cd-Zn-Cu-Hg. The overall results of this thesis provide initial baseline information to evaluate the sensitivity of H. rubra to trace metal toxicants, and these results may be utilised by regulators for establishing marine water quality guidelines to protect H. rubra and other abalone species in their natural habitats.

Over the past few decades, coral cover has declined worldwide due to overfishing, disease, and storms, and these effects have been exacerbated by ocean warming and acidification. Corals are extremely susceptible to these changes because they are already living close to their thermal and aragonite saturation thresholds. Ocean warming and acidification (OAW) may also impact coral survival and growth by impacting their settlement cues. Coral larvae use crustose coralline algae (CCA) and their associated biofilms as cues for settlement, i.e., habitat selection. Settlement cues can also be negatively affected by increased water temperature and acidity. It was hypothesized that the impacts of OAW on settlement substrate can further threaten coral persistence by altering/inhibiting larval settlement and potentially decreasing the post-settlement survival and growth of coral recruits. In this study, we 1) assessed the effect of substrate quality (substrate conditioned in ambient or OAW conditions) on settlement of A. agaricites larvae, 2) determined the effect of substrate quality on post-settlement survival and growth of A. agaricites recruits, and 3) determined the effect of ocean warming and acidification on the post-settlement survival and growth of A. agaricites recruits. Aragonite settlement tiles were placed offshore for one month to accrue CCA and associated biofilms, and were then conditioned in either ambient (29°C, 8.2 pH) or predicted future oceanic conditions (31°C, 7.9 pH) conditions for 7 – 10 days. Agaricia agaricites larvae were then introduced to the settlement tiles, and their settlement percentage was calculated. Once a week for 12 weeks after larval settlement, the size, survival, and pigmentation of A. agaricites recruits was recorded. Larvae settled marginally more on optimally conditioned tiles than on tiles previously exposed to OAW conditions (p=0.053). The survival of coral recruits in OAW conditions was greatly reduced, their growth was very limited, and they became paler over time. When reared in ambient conditions, recruits on OAW treated substrate initially displayed higher survival rates than recruits on ambient treated substrate. After 3 weeks in ambient conditions, however, survival rates were similar for recruits on ambient and OAW treated substrate; their growth curves were very similar, and coral recruits became more pigmented over time. Ocean warming and acidification conditions not only directly impacted the growth, survival, and pigmentation of A. agaricites recruits, but it also indirectly affected larval 5 settlement by likely altering microbial composition in bacterial biofilms on the settlement tiles. These results indicate that future conditions of ocean warming and acidification can be deleterious for A. agaricites, particularly after settlement. If the early life stages of scleractinian corals are negatively affected by OAW conditions, successful recruitment throughout the Caribbean and Florida Reef Tract could decrease. As a result, recovery from disturbances could be hindered, thus compromising the sustainability of many coral species and other marine ecosystems that depend on coral reefs for protection, habitat, and food.

碩士
國立中山大學
海洋生物科技暨資源學系研究所
101
The combination of two factors, temperature and salinity might affect zoeal survival and morphological pattern of Thalamita crenata. In order to know the effect, newly hatched zoeae were reared under 45 combinations of temperature and salinity (i.e. combinations of five temperatures variables: 20, 25, 30, 33, 35℃ and nine salinity variables: 18,20,22,25,30,35,38,40,42 psu ). The zoeae were fed with newly hatched Artemia nauplii. The results showed that temperature and salinity as well as the interaction of the two parameters significantly affected the survival rate of zoeae. The effect of temperature at 20℃ and 35℃ resulted in no zoeal survival from zoea to megalopa stage. Under the temperature range of 25~33℃, There is significant difference between the survival rates of zoeae (p < 0.05). High survival rate (above 64%) occurred at temperature range of 25~30℃ and salinity range of 30~35 psu. Survival rate decreased at salinity range of 20,22,25,38 psu. Under 30℃ and 18 psu condition, zoeae could develop into megalopa stage. Temperature, salinity and their interaction also significantly affected zoeal development. At 25℃, the shortest zoeal developmental time to reach megalopa was 18 days under salinity 30 and 35 psu conditions and the developmental time extended to 20 and 21 days under salinity 38 and 20 psu conditions. At 30℃, the shortest zoeal developmental time to reach megalopa was 11 days under salinity 30 psu conditions and the developmental time extended to 23 days under salinity 18 psu conditions. Under 33℃ and 25 psu condition, the zoeal developmental time to reach megalopa ranged from 16 to 22 days. The larval development of Thalamita crenata has five zoeal stages. Four tested zoeae had morphological differences in antennules, maxillule and maxilla in fifth stage which are shown as follow. There are 5 additional setae on the top of antennule exopod . The endite of maxillule coxal has 14 plumose setae; The basal endite has 8 plumose setae. The maxilla basal endite has 8 plumose setae. The scaphognathite has 27 plumose setae. In addition to basic five zoeal stages, an additional zoeal stages was observed from the tested crab. There were evidences suggested that the appearance of the additional zoeae was associated with limited temperature condition for life and lower salinity. Based on exuviae and larval specimens, the major morphological characteristics of the additional zoeal larvae were as follow: oblong carapace, lateral spine disappeared; prolonged cheliped and pereiopods compared to Z5 stage; with setae on pleopods.

碩士
國立中山大學
海洋生物學系
85
This research studied the effects of larval density on the larval development rate and benthic juvenile growth of Babylonia formosae (Sowerby). Larvae were collected and raised at four densities (1, 2, 4 and 8 individuals/ml) and physiological traits in different developmental stages were recorded. Results show that increasing planktonic larval density increased cumulative settlement rate and decreased mortality rate and settlement time. The densities of planktonic period were not related to the daily growth and total shell length increment of juveniles in the settled juveniles under control treatment. Daily growth and total shell length increment of juveniles decreased with increasing densities of settled juveniles in the settled juveniles under experimental treatment. The increased cumulative settlement rate and decreased mortality rate caused by the increment of planktonic larval densities may be explained by the concentration of inducer in the environment. Enhanced development rate may be caused by the lack of food competition during the planktonic period. Increasing settled juvenile density accompany by decreased daily growth and total shell length increment of juveniles is a common negative effect caused by high density in an organism.

Larval development of Berthella californica, a pleurobranchoidean heterobranch from the Northeastern Pacific, is described using histological sectioning, SEM, TEM, and immunolabelling. Current phylogenetic hypotheses place the Pleurobranchoidea as sister to all nudibranchs, or as sister to only the anthobranch nudibranchs. Deciding between these alternatives is difficult due to extensive homoplasy among heterobranchs. Analysis of larval morphology may help resolve this issue by identifying additional phylogenetically informative characters. Larval development has been well documented for many nudibranchs, but there are few studies on pleurobranchoideans. Larvae of B. calfornica dissolve internal shell whorls, a trait uniquely shared with nudibranch larvae. Additionally, mantle fold tissue inflates and reflects dorsally during metamorphosis to form the notum, which also occurs in anthobranchs. B. californica possesses several unusual developmental traits, as revealed by a review of current knowledge of heterobranch development. Morphological characters of B. californica larvae support hypotheses of nudibranch paraphyly and the clade Pleuroanthobranchea.

The flat or native oyster, Ostrea angasi (Sowerby, 1871), was once a conspicuous inhabitant of many coastal bays and estuaries in south eastern Australia and formed the basis of a thriving wild fishery. Overfishing led to population collapses in NSW, Victoria, Tasmanian and South Australia, which in turn saw local demand for oysters being met through the production of Sydney rock oysters and the introduced Pacific oyster. As markets have developed and factors such as disease have impacted the production of other oyster species, there has been a renewed interest in production of O. angasi within the southern states. O. angasi are sequential protandric hermaphrodites and larviparous, with brooding adults retaining larvae on the gill filaments in the brachial chamber for approximately half the larval life cycle. Wild catch of O. angasi spat is low and unreliable and the cultivation of this species is reliant upon hatchery production. To date production techniques for O. angasi have been loosely based on those used for Saccostrea glomerata and Crassostrea gigas, and have varied in success, with many hatcheries still reporting poor outcomes. In part this has arisen from a lack of systematic assessments of the fundamental variables that determine hatchery success. Specifically, improvements in O. angasi production output and reliability require an improved understanding of the reproductive biology of the species and knowledge of conditions required to optimise late larval development and metamorphosis. In the first instance hatchery production is underpinned by the reproductive biology and ecology of this species. Knowledge of the temporal frequency of reproduction within New South Wales (NSW) estuaries is essential for larval acquisition and the development of a hatchery program. To address this, oysters were sampled over a 12 month period, across four estuaries, and examined histologically to reveal marked differences in gametogenic patterns to that previously reported in the southern states of Australia. The frequency of brooding oysters among farmed populations of O. angasi, in NSW waters, extended beyond that recorded in the Southern states of Australia. In the most northern and southern estuaries examined, brooding oysters were found between eight to nine months of the year with little synchronicity observed in reproductive timing within and between estuaries. Temperature, previously thought to halt gametogenic activity, was not restrictive to O. angasi reproduction in NSW farmed populations. For oviparous oyster species, assessments of larval rearing techniques frequently address specific ontogenetic stages, which begin with fertilisation success and culminate in competency and metamorphosis. For O. angasi, advanced stage larvae are acquired directly from brood-stock and greater emphasis is on the settlement and metamorphosis. This study sought to better understand the influence of the larval rearing environment on the morphological changes and physiological mechanisms associated with metamorphosis in O. angasi. Accordingly, techniques to reliably induce metamorphosis in competent larvae were assessed, and based upon these outcomes the impact of diet, temperature and salinity on later stage larvae were assessed, all with a view to improve O. angasi hatchery outcomes. Several neuroactive catecholamines (epinephrine, epinephrine bitartrate, L-3,4- dihydroxyphenalalanine and gamma amino butyric acid) were trialed to induce metamorphosis of O. angasi larvae. The optimal dose and duration of exposure of epinephrine and epinephrine bitartrate was determined by induced metamorphosis of O. angasi larvae. The capability to induce rapid metamorphosis in competent O. angasi, aside from single seed production for industry, offers an invaluable tool to assess the effects of rearing conditions on larval development and acquisition of competency. Using epinephrine induced metamorphosis, the influence of algal diet, rearing salinity and temperature on survival, growth and development of hatchery reared O. angasi, larvae was investigated. A comparison of dietary requirements for early stage larvae (140 - 230μm shell length) and late stage larvae (230 - 340μm shell length) was made. A series of uni, binary and ternary algal diets were assessed for their effect on the development of competency by induced larval metamorphosis. Optimal salinity (30 to 35) and temperature (26 to 29oC) were determined for larval rearing, larvae reared outside these salinity and temperature range exhibited, reduced growth, survival and/or delayed development. The effects of short term (1h) reduction in larval rearing temperature from 26oC significantly increased larval metamorphosis without affecting larval survival. However, short term increase in larval rearing temperature from 26oC adversely effected larval survival and metamorphosis, high lighting the need to assess rearing conditions during this critical stage of development. To ensure repeatability in outcomes, tests showed larvae sourced from different estuaries did not vary significantly in their metamorphic response to short term temperature manipulation and epinephrine induced metamorphosis. Collectively the work in this thesis has significantly increased our understanding of O. angasi reproductive patterns and larval biology. The seasonal availability of larvae and the effects of the main environmental factors purported to influence reproduction of O. angasi have been examined. The environmental factors that can be easily and economically adjusted for greater larval rearing success were determined. Additionally, this work adds to the broader understanding of the acquisition of competency and larval metamorphosis in bivalve molluscs. Commercially, O. angasi hatchery outcomes have been highly variable; however, beyond having developed protocols for the use of settlement inducers, significant improvements in hatchery success have accrued. At the Port Stephens Fisheries Institute, a facility that has produced commercial quantities of O. angasi spat for over 15 years, the cumulative improvements in larval rearing technology described in this thesis have increased the percentage of larvae that successfully metamorphose from an historical average of approximately 57% for the four most successful rearing attempts to an overall average of 68% for nine larval rearing attempts.

Cannibalism is a seemingly aberrant interaction, appearing counter to the fitness of individuals. Yet cannibalism is not overly uncommon, and naturally occurs among aquatic organisms, including larval amphibians. In temporary wetlands larval amphibians are in a race to complete metamorphosis before their aquatic habitat disappears. When intraspecific competition intensifies, eating conspecifics may represent a beneficial if not necessary strategy. The research presented within this thesis aims to characterize factors that influence cannibalism within populations of larval amphibians. Wood frog tadpoles (Lithobates sylvaticus) were used to test potential benefits of cannibalism as a diet, determine if dietary quality and nutritional stress influence cannibalism, and investigate the roles of competition and chemical cues in influencing cannibalism. Larval long-toed salamanders (Ambystoma macrodactylum), and ringed salamanders (A. annulatum) were used to investigate a functional link between trophic polymorphism and cannibalism in natural populations. Results suggest that perceived increases in competition may stimulate some individuals to become less risk averse, and more aggressive, which may in turn facilitate cannibalistic behaviour. Cannibalism itself provided only conditional benefits to larval wood frogs, rather than the optimal growth that would be expected from an ideal diet. However, this may have been the result of individual variation in response to the diet and/or conspecific cues as opposed to a nutritional deficit. In conditions where tadpoles could perceive increased competition they altered their behaviour and morphology in ways that may improve their foraging success and potentially promote cannibalism. Finally, a functional link appears to exist between head morphology and cannibalism in natural wetlands. However, the appearance of this morphology appears related to conditions that may facilitate increased population densities through rapid pond drying.

Perfluoroalkyl substances are synthetic organic chemicals of environmental concern because they have been associated with adverse effects in both human epidemiological studies and standard laboratory animals. In the environment, PFAS occur as mixtures, especially in areas with a history of PFAS application, such as aqueous film forming foam (AFFF) sites. Among the PFAS, perfluorooctanesulfonic acid (PFOS) and perfluorohexanesulfonic acid (PFHxS) are the most common, and occur at the highest concentrations. Thus, amphibian populations at or near AFFF sites are at risk of exposure to known bioaccumulative and persistent chemicals, likely compromising the physiology and body condition of the animals. Here, we exposed northern leopard frogs to environmentally relevant concentrations of 0.5 and 1 ppb PFOS and PFHxS, alone or as a mixture comprised of 0.5 ppb PFOS and 0.5 ppb PFHxS. Univariate analyses showed that in the larval stages, tadpoles exposed to PFAS had significantly reduced scaled mass indexes (SMI’s) relative to the control, and only the organisms exposed to PFHxS 0.5 ppb were significantly larger. Sex did not significantly influence toxicity in the later stages (GS 42 & 46), indicating no sex-related effects. Altered body condition (i.e., fat stores) in the larval stages indicate potential effects to energy balance. There is a need to assess fitness-related effects as amphibians’ transition into the terrestrial environment, and include endpoints such as: reproductive, developmental, immunological, mating, feeding, competition, and survival. Early developmental effects in the larval stages also suggests that earlier developmental endpoints may be of interest. Establishing ecological risk assessments for PFAS are necessary, as they are toxic, persistent, and bioaccumulative.

The increase of ultraviolet radiation (UV) and the increasing use of personal care products (PCP) are referred as two of the main anthropogenic-driven threats that can affect aquatic species. The early larval stages of Senegalese sole, Solea senegalensis, Kaup 1858 are among the marine vertebrates potentially affected by these stressors. Therefore, the objective of this work is to study the single and combined effects of UV and two PCP ingredients along early development of the sole, the wide-spectrum biocidal triclosan (TCS) and the UV filter 4-methylbenzylidene camphor (4-MBC). The TCS, 4-MBC and UV exposure tests were performed on two stages of larval development: from egg to 3 days after hatching (approximately 96 hours post-fertilization) and throughout the initial 48 h of metamorphosis (typically near the thirteenth day after hatching) with evaluation of the development until the end of the metamorphosis (about ten days later). Effects at the individual level (survival, malformations, growth, behavior, and progression of metamorphosis) were linked with effects at lower organizational levels (biochemical and molecular markers). In general, the response to the exposure to sub-lethal levels of different stressors indicates that the initial larval stage is more sensitive than the metamorphosis stage. At the end of the first stage of development, exposure to the stressors caused a decrease in growth and induced malformations. At biochemical level, the exposure to 4-MBC and UV did not affect the cholinergic activity in an evident manner, however changes were observed at behavioral level, namely a decrease of swimming activity. Additionally, at this stage, the GST was induced by TCS (LOEC = 30 μg L-1 TCS), suggesting activation of the phase II of biotransformation for detoxification. At the end of the metamorphosis, effects of chemicals exposure were observed even after maintenance in clean medium for nine days, namely alterations on antioxidant system and decrease of growth. Additionally, both chemical stressors caused an acceleration of the metamorphosis progression during exposure and also in the immediately subsequent moments. This response suggests a possible direct or indirect action of these stressors on thyroid axis. In the case of TCS, this action was verified through the observation of the down-regulation of thyroid axis genes (NIS and TSHβ), which lasted until the end of metamorphosis in one of the analyzed genes (NIS). There was also a down-regulation of genes both immediately after exposure to UV (THRβ, Tpo and NIS) and at the end of metamorphosis (NIS). The changes may be related to oxidative damage in thyroid tissues caused directly by UV, which can lead to dysfunction of this gland. However, this under-expression of the thyroid genes of UV-exposed organisms was not followed by alterations in the progression of metamorphosis at individual level. Overall, the results obtained suggest that the sole response to TCS was not altered when in combination with UV. In general, the results obtained in the present study suggest that exposure to stressors may have an impact on the development and ecological performance of the species. Additionally, taking into account the modes of action of the stressors and the relevant effects observed, studies in more realistic scenarios should be performed, namely, considering longer periods of exposure using environmentally relevant concentrations/doses. The usefulness of larval stages of sole as a model species to evaluate stressors effects in the marine environment was confirmed, with the initial early period up to the third day after fertilization being a suitable alternative model for animal testing.
O aumento da radiação ultravioleta (UV) e a utilização crescente de produtos de cuidado pessoal (PCP) têm sido apontados como duas das ameaças derivadas da ação humana que podem afetar espécies aquáticas. Os estadios larvares de linguado branco, Solea senegalensis, Kaup 1858 estão entre os vertebrados marinhos potencialmente afetados por estes stressores. Assim, o objetivo deste trabalho é estudar, ao longo do desenvolvimento larvar do linguado, os efeitos simples e combinados de radiação UV e de dois ingredientes de PCP, o biocida de largo espectro triclosan (TCS) e o filtro UV 4-metilbenzilideno-cânfora (4-MBC). Foram realizados testes de exposição a TCS, 4-MBC e UV em duas fases do desenvolvimento larvar do linguado: desde ovo até aos 3 dias após eclosão (aproximadamente 96 horas pós-fertilização) e ao longo das 48 h iniciais da metamorfose (tipicamente ao décimo terceiro dia após a eclosão) com avaliação do desenvolvimento até ao final da metamorfose (cerca de dez dias mais tarde). Estudaram-se efeitos ao nível do indivíduo (sobrevivência, malformações, crescimento, comportamento e progressão da metamorfose) que se tentaram ligar com efeitos a níveis organizacionais inferiores (marcadores bioquímicos e moleculares). De um modo geral, a resposta à exposição a níveis sub-letais dos diferentes stressores indica que o estadio larvar inicial é mais sensível que a fase da metamorfose. No final da primeira fase de desenvolvimento estudada, a exposição a cada um dos stressores causou diminuição do crescimento e induziu malformações. A nível bioquímico, a exposição a 4-MBC e UV não afetou a atividade colinérgica de forma evidente, no entanto observaram-se alterações a nível comportamental, nomeadamente uma diminuição da natação. Adicionalmente, nesta fase, observou-se a indução da GST pelo TCS (LOEC=30 μg L-1 TCS), sugerindo ativação da via biotransformação II para destoxificação. Da análise dos efeitos dos stressores químicos no final da metamorfose, verifica-se que estes causam efeitos mesmo após manutenção durante nove dias em meio limpo, nomeadamente a nível de stress oxidativo e diminuição do crescimento. Adicionalmente, ambos os stressores químicos causaram uma aceleração da progressão da metamorfose durante a exposição e também nos momentos imediatamente subsequentes. Esta resposta sugere uma possível ação direta ou indireta destes stressores no eixo da tiroide. No caso do TCS, esta ação foi verificada através da observação da sub-expressão de genes do eixo da tiroide (NIS e TSHβ), que se prolongou até ao final da metamorfose num dos genes analisados (NIS). Verificou-se ainda uma sub-expressão de genes tanto imediatamente após a exposição aos UV (THRβ, Tpo e NIS) como no final da metamorfose (NIS). Estas alterações podem estar relacionadas com o dano oxidativo nos tecidos da tiroide causado diretamente pelos UV, o que pode levar à disfunção desta glândula. No entanto, esta sub-expressão dos genes da tiroide dos organismos expostos aos UV não foi acompanhada por alteração da progressão da metamorfose ao nível do indivíduo. Globalmente, os resultados sugerem que a resposta do linguado ao TCS não foi alterada pela exposição combinada com UV. De um modo geral, os resultados obtidos neste trabalho sugerem que os stressores estudados poderão ter impacto no desenvolvimento e na performance ecológica da espécie. Adicionalmente, tendo em conta os modos de ação dos stressores e os efeitos relevantes observados, deverão ser realizados estudos em cenários mais realistas, nomeadamente, por períodos de tempo mais prolongados e utilizando concentrações/doses ambientalmente relevantes. A utilidade de estadios larvares do linguado como modelos na avaliação de efeitos de stressores em ambiente marinho foi confirmada, sendo que o período inicial até aos três dias pós-fertilização se enquadra como modelo alternativo em experimentação animal.
Programa Doutoral em Biologia e Ecologia das Alterações Globais

Members of the Pyramidellidae are ectoparasites that have highly unusual feeding habits relative to other heterobranch gastropods. Pyramidellid foregut anatomy is so complex that it is difficult to recognize homologous parts relative to other heterobranch gastropods, which is a necessary step in reconstructing evolutionary changes to the foregut developmental program. We investigated foregut development through metamorphosis and beyond in the pyramidellid Odostomia tenuisculpta. By examining sections of larval and post-velum loss stages, we conclude that the so-named acrembolic proboscis of this pyramidellid is actually an eversible oral tube and the piercing stylet is either a modified radular tooth or a jaw derivative. Much of the complex, multi-component foregut of the post-metamorphic stage is constructed during a 10-day period of explosive metamorphic morphogenesis. This stands in marked contrast to predatory neogastropods, where most components of the adult feeding system become extensively differentiated in the larval stage prior to settlement and metamorphosis.
Graduate
2020-06-10

碩士
國立臺灣大學
生態學與演化生物學研究所
107
Microplastics are plastic debris smaller than 5 mm in diameter. It has been shown that microplastics would cause many adverse impacts on zooplanktons such as reduce feeding rate, delay development and decrease fecundity. However, most studies evaluate the effect of microplastics focus on holoplankton, but relatively less studies focus on meroplankton. In the present study, we used the barnacle Amphibalanus amphitrite as a model organism for meroplankton to investigate the effects of four different sizes of polystyrene microplastics (diameter 1.7, 6.8, 10.4, 19.0 µm respectively) at four concentrations (1, 10, 100, 1000 beads mL-1). We found that stage II nauplii of A. amphitrite were able to ingest all four sizes of microplastics and efficiently egested them within several hours. Larval mortality, development time, growth rate, settling rate and metamorphosis percentage of microplastic treatments were not significantly different from that of control after being exposed to four different sizes of microplastics at any concentration from nauplii to cyprids. Moreover, feeding rate of nauplii (stage II- stage VI) were barely impaired at the concentration of 1000 beads mL-1. Overall, our results suggest that polystyrene microplastics have very limited impacts on the entire larval cycle of barnacle A. amphitrite. The microplastic exposed larvae could still successfully metamorphose to juvenile stage. We further extended the microplastic exposure over barnacle generations, continuously fed barnacle adults with same size of microplastic until they reproduced next generation offspring. Our results found that microplastics did not significantly affect adults of first generation but significantly increase larval mortality of next generation offspring, suggesting that microplastics have transgenerational effects. We also compared the larval mortality and retention time of microplastics between barnacle larvae from different habitats and climatic zones (Fistulobalanus albicostatus, Tetraclita japonica formosana, Chelonibia testudinaria, Neoacasta sp., Euacasta dofleini, Darwiniella angularis, Chthamalus dalli, Balanus glandula). We found that all barnacle species did not suffer increase mortality upon exposure to microplastics, but the retention time of microplastics significantly differed between barnacles lived in different habitats. Rocky shore and coral reef associated species have about 3-4 times longer microplastic retention time than the muddy shore species, suggesting that rocky shore and coral reef associated species might be more vulnerable to microplastic pollution.

The series of two fossil species belonging to the order Palaeodictyoptera from the Late Carboniferous of Kuznetsk Basin in Russia were re-examined. The two species as Tchirkovaea guttata and Paimbia fenestrata were investigated with emphasis on the wing growth and development in comparison with the structure of developing wings in recent mayflies. This fossil material of T. guttata and P. fenestrata was long considered by previous authors as undisputed evidence for a unique type of wing development in the Palaeozoic insects. The idea was that the larvae of these insects possessed the wings, which became articulated and fully movable already earlier during the postembryonic development and that these gradually growing wings changed their position from longitudinal to perpendicular to the body axis. Moreover, the development was supposed to include two or more subimaginal instars, implying that the fully winged instars moulted several times during postembryonic development. After detailed study of the available fossils and subsequent comparison of the fossil evidence with the development of wings in the recent mayfly Cloeon dipterum it was discovered, that the alleged series of immature, subimaginal and imaginal wings of T. guttata and P. fenestrata do not provide clear evidence that would support...

Η οικολογία και η δυναμική της εγκατάστασης εξετάστηκαν για τέσσερα μεσογειακά παράκτια είδη: Diplodus vulgaris, Diplodus sargus, Oblada melanura και Diplodus annularis. Η διερεύνηση τους έγινε με υποδιαίρεση της βενθικής ιχθυονυμφικής τους φάσης σε έξι οντογενετικά στάδια βάσει χρωματικών πρότυπων που εμφάνιζαν διαδοχή και ήταν χαρακτηριστικά για κάθε είδος. Η συλλογή δεδομένων έγινε για κάθε οντογενετικό στάδιο με στρωματοποιημένη δειγματοληψία, με τις στρώσεις να αποτελούν συνδυασμό τύπου υποστρώματος και βάθους στην παράκτια περιοχή ανατολικά των εκβολών του Αχελώου, από βάθος 0 έως 5m. Τα δεδομένα συλλέχθηκαν με απ’ ευθείας παρατηρήσεις με χρήση καταδυτικής συσκευής. Υπολογίστηκαν οι πυκνότητες κάθε οντογενετικού σταδίου στους διάφορους τύπους υποστρώματος και βάθη μέσα στο έτος. Η κατανομή των πυκνοτήτων αυτών έδωσε στοιχεία για τις οικολογικές προτιμήσεις των βενθικών ιχθυονυμφών και των νεαρών, καθώς και για τους ρυθμούς μεταμόρφωσης κάθε είδους. Επίσης ελέγχθηκε το πρότυπο συμπεριφοράς των ιχθυονυμφών του μελανουριού κατά την εγκατάσταση τους, μ’ επινόηση ειδικής μεθοδολογίας κι ενός δείκτη που απέδωσε ποσοτικά τις διάφορες εκφάνσεις της συμπεριφοράς. Σύμφωνα με τ’ αποτελέσματα της εργασίας, φάνηκε ότι ο σαργόπαπας και ο σαργός εγκαθίστανται την κρύα περίοδο του έτους, ενώ το μελανούρι και ο σπάρος τη θερμή. Όλα τα είδη εμφάνισαν γρηγορότερο ρυθμό μεταμόρφωσης κατά τα πρώτα στάδια, ενώ τα είδη που εγκαταστάθηκαν το καλοκαίρι είχαν συνολικά γρηγορότερους ρυθμούς μεταμόρφωσης από τα χειμερινά. Τα είδη εμφάνισαν διαφοροποίηση στη χρονική και χωρική κατανομή τους ώστε να ελαττώνονται οι ανταγωνιστικές δράσεις. Το είδος με τη μακρύτερη χρονική παρουσία ήταν ο σαργόπαπας (10 μήνες), ο οποίος εμφάνισε ευρύτητα ως προς τις οικολογικές του απαιτήσεις διασπειρόμενος σ’ όλο το εύρος βάθους και τύπους υποστρώματος, εκτός του αμμώδους. Στον αντίποδα, το μελανούρι είχε τη μικρότερη συνολική παρουσία (4 μήνες) και απόλυτη εξάρτηση από σκληρό υπόστρωμα. Ο σαργός κι ο σπάρος έδειξαν ενδιάμεσες οικολογικές απαιτήσεις με προτίμηση στα σκληρά υποστρώματα και στα φανερόγαμα αντίστοιχα. Κανένα είδος δεν έδειξε προτίμηση σε αμμώδεις βυθούς. Ιδιαίτερο οικολογικό ρόλο εμφάνισε το ρηχότερο τμήμα της παράκτιας ζώνης και οι μεταβατικές ζώνες διαφορετικών υποστρωμάτων. Οι βενθικές ιχθυονύμφες του μελανουριού επέδειξαν τάση παραμονής για μέρες με μικρές ομάδες σε σημεία του υποστρώματος. Στα επόμενα στάδια σχημάτισαν μεγάλες ομάδες με μικρότερη εξάρτηση από το υπόστρωμα.
The ecology and dynamics of settlement process were studied for four sparids (Diplodus vulgaris, D. sargus. D. annularis and Oblada melanura), in a coastal littoral in western Hellas. The benthic larval phase of each species was divided in six ontogenetic stages, according to specific patterns in appearance that followed a sequence. Preliminary observations showed non homogeneous distribution of the larvae in the area, so stratified sampling was applied. Strata represented the different substratum types accounted in each of the three depth zones of 0-1m, 1-2m and 2-5m. Data concerned abundances of each ontogenetic stage in each stratum during a 15 month interval and they were collected by visual census. Moreover, data on site-attachment ontogenetically depended behavior of benthic larvae of O. melanura were also collected. The later behavior was studied via an index devised for quantifying different expressions of residence behavior. Two of the studied species (D. vulgaris and D. sargus), settled during the cold period of the year while the other two settled during summer. Metamorphosis rates were faster at the first ontogenetic stages for all species, while they were faster in total for the summer species. Temporal and spatial distribution of the species was arranged in order to minimize competition. D. vulgaris and D. sargus settled in the same substratum types in different periods and O. melanura and D. annularis settled during the same period in different substrata. D. vulgaris remained in the nursery area the longest period, exhibiting the broadest ecological requirements, being distributed in different substrata and depths. O. melanura remained half as long in the nursery area, exhibiting the narrowest ecological requirements, staying always over hard substratum in shallow waters. The other two species exhibited intermediate conditions, with D. sargus preferring hard substratum and D. annularis, seagrass beds. None of the studied species preferred soft substratum. The shallowest part of the littoral appeared to be very important for three species (D. vulgaris, D. sargus, O. melanura) and the transition zones (between two different substrata), for all four of them. Benthic larvae of Oblada melanura commenced settlement in small shoals that resided for varying number of days in specific sites over stones or rocky substratum. Gradually as metamorphosis proceeded they became more kinetic forming larger shoals that expanded their home range.