Academic literature on the topic 'Aquatic molluscs'

Vibrio spp., natural inhabitants of aquatic environments, are one of the most common causes of bacterial gastroenteritis in the world, being spread to humans via the ingestion of seafood, contaminated drinking water or exposure to seawater. The majority of Vibrio spp. are avirulent, but certain strains may sporadically be human pathogenic. Vibrio cholerae may cause cholera and fatal wound infections, Vibrio parahaemolyticus may cause gastroenteritis and Vibrio vulnificus may cause wound infections and sepsis. To expand current knowledge of the occurrence, ecological niche and persistence of potential human pathogenic Vibrio spp. in aquatic environments, occurrence and laboratory studies were performed. The seasonal variation of Vibrio spp. in clams and mussels from Mozambique and Sweden were studied, with isolated strains characterized and compared with those isolated from water samples collected in India. Results showed that the numbers of Vibrio spp. in Mozambican clams peaked during the warmer rainy season and that the dominating species was V. parahaemolyticus. Biochemical fingerprinting and virulence screened by PCR revealed a high similarity among strains from the different aquatic environments. However, isolate functional hemolytic analyses and antibiotic resistance patterns differed between strains; Swedish and Indian strains were less sensitive to the tested antibiotics and had a lower hemolytic capacity than those from Mozambique. Molecular analysis of bacterial DNA from Swedish mussels showed the presence of the three Vibrio spp. most commonly linked with human illness, as well as their associated virulence genes. The strains isolated from marine and clinical environments were equally and highly harmful to the tested eukaryotic cells. The persistence of clinical V. cholerae in aquatic environments was investigated in vivo. Strains were exposed to mussels, with bacterial uptake and elimination then examined. The mussels were able to avoid the most potent strain by complete closure of shells. The less potent strain was accumulated in mussel tissue in low levels and one marine control strain to a higher degree. Mussels eliminated the pathogenic strain less efficiently than they did the marine strain. One clinical and one marine strain were then exposed to 4°C for 21 days, with the temperature then increased to 20°C. The clinical strain was more prone to lose culturability than the marine strain at 4°C, the former performed significantly better in regaining culturability after the temperature up-shift. Subsequently, the persistence of the clinical strain in natural bottom sediment, incubating as above, was studied and results showed a similar decrease in culturable numbers in the sediment as in the water. As the clinical V. cholerae strains did not carry any of the standard set of virulence genes, the ability to change from non-culturable to culturable may be of great importance to strain pathogenicity. The results also show that natural bottom sediment may be a potential reservoir of human pathogenic Vibrio spp.

This thesis covers three important aspects of Antarctic heterobranchs: ecology, taxonomy, and systematics. The first section deals with ecological interactions of several nudibranchs. In Chapter 1, we chemically characterize a new natural product (a homosesterterpene) called granuloside, from Charcotia granulosa Vayssière, 1906; remarkably, this is the first record of this type of compound in marine organisms. In Chapter 2, we assess the origin, function, and distribution of granuloside in this nudibranch; we found glandular structures probably responsible for storing granuloside, as a defensive mechanism against predators, like the sympatric starfish, Odontaster validus Koehler, 1906. We also hypothesize that granuloside is de novo biosynthesized by C. granulosa. This chapter reflects how organisms from polar latitudes have similar defensive strategies to those of temperate and tropical zones. In Chapter 3, a new species of ectosymbiont copepod, Anthessius antarcticus n. sp., living on C. granulosa is described. This is the first record of such association in Antarctica and the first time that this copepod genus has been found living on a nudibranch. In Chapter 4, we study the development of two anthobranchs, Doris kerguelenensis (Bergh, 1884) and Bathydoris hodgsoni Eliot, 1907, both with intracapsular development; we provide new data on the egg masses characteristics, and embryos morphology and anatomy, throughout their development; we also studied at which ontogenetic stage their natural products appear. We concluded that both nudibranchs exhibit developmental periods of up to several years; their embryos are physically defended by a thick egg capsule, while juveniles already rely on de novo biosynthesized defensive compounds. In the second section of this thesis, our interdisciplinary taxonomic and systematic studies, including histology, tomography, electron microscopy, and molecular tools, allowed us to describe three new species of heterobranchs. In Chapter 5, we provide integrative taxonomic evidence for the establishment of a new family (Newnesiidae), and the description of a new species of Cephalaspidea (Newnesia joani n. sp.) with eurybathic and circumpolar distribution; this discovery traces the origin of the cephalaspideans (distributed worldwide) to Antarctica. In Chapter 6, we performed a three-dimensional (3D) anatomical reconstruction and compared the two nudibranchs Doto antarctica and the new species Doto carinova n. sp.; their phylogeny reveals intriguing questions concerning the development of the reproductive system in this genus; 3D reconstructions reveal also the presence of probable giant neurons associated with the nervous system, which were unknown in this genus so far. Finally, in Chapter 7 we provide new evidence of bipolar geographic distributions by describing a new species of nudibranch, Doridunculus punkus n. sp., using only non-destructive tomographic techniques. Our results highlight both the need and the relevance of multidisciplinary approaches to study biodiversity and ecological interactions in heterobranch molluscs from a poorly studied area of the planet, such as Antarctica.<br>Esta tesis doctoral abarca tres aspectos relevantes de los heterobranquios antárticos: su ecología, taxonomía y sistemática. La primera sección trata sobre interacciones ecológicas en varios nudibranquios. En el capítulo 1, caracterizamos químicamente un nuevo producto natural (un homosesterterpeno) denominado granuloside, de Charcotia granulosa Vayssière, 1906; cabe destacar que ésta es la primera vez que se halla este tipo de compuestos en organismos marinos. En el capítulo 2, evaluamos el origen, función y distribución del granuloside en dicho nudibranquio; hallamos estructuras glandulares probablemente encargadas de acumular granuloside como mecanismo defensivo frente a depredadores, como la estrella de mar Odontaster validus Koehler, 1906. Además, sugerimos que C. granulosa biosintetiza granuloside de novo. Este capítulo refleja cómo los organismos de latitudes polares poseen estrategias defensivas similares a los de las zonas templadas y tropicales. En el capítulo 3, se describe una nueva especie de copépodo, Anthessius antarcticus n. sp., ectosimbionte de C. granulosa; este es el primer registro de este tipo de asociaciones en la Antártida y la primera vez que se describe este género viviendo en un nudibranquio. En el capítulo 4, estudiamos el desarrollo de dos antobranquios, Doris kerguelenensis (Bergh, 1884) y Bathydoris hodgsoni Eliot, 1907, con desarrollo intracapsular; aportamos nuevos datos morfológicos y anatómicos sobre las puestas, huevos y embriones a lo largo de su desarrollo; también estudiamos el estadio ontogenético en el que aparecen sus productos naturales; concluimos que ambas especies tienen periodos de desarrollo de varios años, sus embriones se defienden físicamente gracias a la gruesa cápsula del huevo, mientras que los juveniles ya sintetizan sus propios compuestos defensivos. En la segunda sección de la tesis, nuestros estudios taxonómicos y sistemáticos interdisciplinares, incluyendo técnicas de histología, tomografía, microscopía electrónica y moleculares, han permitido la descripción de tres especies nuevas de heterobranquios. En el capítulo 5, se aporta evidencia taxonómica para establecer una nueva familia (Newnesiidae), y la descripción de una nueva especie de Cephalaspidea (Newnesia joani n. sp.) con distribución euribática y circumpolar; este descubrimiento traza el origen de los cefalaspideos (distribuidos en todo el mundo) hasta la Antártida. En el capítulo 6, realizamos una reconstrucción anatómica tridimensional (3D) y comparamos los dos nudibranquios Doto antarctica y la nueva especie Doto carinova n. sp.; su filogenia revela interesantes cuestiones relativas a la evolución del sistema reproductivo en este género; además, las reconstrucciones 3D revelan la existencia de posibles neuronas gigantes asociadas al sistema nervioso, hasta ahora desconocidas en este género. Por último, en el capítulo 7, proporcionamos nuevas pruebas de una distribución geográfica bipolar, mediante la descripción de una nueva especie de nudibranquio, Doridunculus punkus n. sp., usando exclusivamente técnicas tomográficas no destructivas. Nuestros resultados ponen de manifiesto la necesidad y la relevancia de utilizar enfoques multidisciplinares para el estudio de la biodiversidad y las interacciones ecológicas en moluscos heterobranquios, en especial en un continente todavía poco estudiado, como es la Antártida.

Globalization has seen an unprecedented dispersal of exotic and alien species worldwide resulting in worldwide homogenization and sometimes extinction of indigenous or endemic taxa. When an exotic species becomes established in a new habitat the invasive organisms are capable of having an impact on indigenous community dynamics and the overall structure and function of ecosystems. Furthermore, the impact of invasion is determined by the geographical range, abundance and the per-capita or per-biomass effect of the invader. However, the success of the introduced organisms is reliant on their ability to acclimate to the physiochemical conditions of the newly invaded environment.Freshwater ecosystems are especially vulnerable to invasions because there are numerous potential routes of introduction including intentional pathways such as stocking, and unintentional pathways such as the release of ballast water and aquarium releases. Efforts to limit the introduction of invasive species or to manage established exotic populations are often hindered by insufficient understanding of the natural history of problematic species. Relatively little is known regarding the physiological tolerances of many taxa. Knowledge about specific species ecophysiological constraints allows for the prediction of future patterns of invasion more accurately, including where an introduced organism would probably survive, thrive and disperse. Furthermore, data on the physiological tolerances of an introduced exotic organism may provide data necessary for effective management and control. This studyinvestigated three invasive species in the Nseleni River system in a protected area in KwaZulu-Natal. The species studied were, Tarebia granifera (Quilted melania – Lamarck, 1822), Pterygoplichthys disjunctivus (Suckermouth armoured catfish - Weber, 1991) and Eichhornia crassipes (water hyacinth – (Martius) Solms-Laubach,). The Nseleni River flows into Lake Nsezi which is responsible for providing potable water to the surrounding towns and industry, as well as the surrounding rural communities. The Enseleni Nature reserve has become the centre for biodiversity dispersal in the immediate area, due to the change in landscape surrounding the protected area.An important step in developing alien invasive species management strategies in protected areas is determining their extent and invasive traits. Tarebia granifera is a prosobranch gastropod originally from South-East Asia that has become invasive in several countries around the world including South Africa. Snail populations were sampled at nine sites throughout the Nseleni/Mposa river system every six weeks over a twelve month period. The snail was abundant throughout the system, especially in shallow waters of less than 1m in depth.The first positive identification the loricariid catfish Pterygoplichthys disjunctivus for the Nseleni River was in 2006. The original introduction is believed to have been via the aquarium trade. The aim of the study was to assess the usefulness of the unified framework with regard to management of fish invasions by assessing the invasion stage of the loricariid population and identifying appropriate management actions using the Blackburn et al. (2011) framework. The fish were sampled at nine different sites and three different depths over a period of twelve months, as well as when two ichthyological surveys were carried out on the Nseleni River system. This invasive fish has been located throughout the system and both male and female fish were collected. The smallest fish sampled was a fingerling of a day or two old and the smallest pregnant female was a mere 270mm TL. This is a clear indication that this fish is breeding in the river system.Although T. granifera and P. disjunctivus were abundant in the Nseleni/Mposa river system, it was not clear what their role in the system was, and in particular if they were competing with any of the indigenous species. Therefore, isotope samples were collected from numerous taxa over a two week period, with the exception of Pterygoplichthys disjunctivus samples, which were collected over 12 months. The δ13C and δ15N signatures of all samples were determined. The niche overlap between the invasive and indigenous snails was effectively zero (1.02E-13%), indicating no shared food resources. The medium ranges of dNRb (7.14) and dCRb (9.07) for the invasive fish indicate that it utilizes a wider range of food resources and trophic levels than the majority of indigenous fish. A medium CDb value (2.34) for the invasive fish species, P. disjunctivus, describes medium trophic diversity, with three indigenous species possessing higher diversity and three possessing lower diversity. Furtherresults indicated that there was no direct dietary competition between P. disjunctivus and indigenous species. Eichhornia crassipes was first recorded on the Nseleni River in 1978, and has been shown to have a significant negative impact on the biodiversity of the Nseleni/Mposa River system and therefore required a control intervention. Although biological control using the two weevil species Neochetina eichhornia (Warner) and N. bruchi (Hustache) has been credited with affecting a good level of control, the lack of a manipulated post-release evaluation experiments has undermined this statement. Five experimental plots of water hyacinth of 20m2 were sprayed with an insecticide to control weevils. After ten months the plants in the sprayed plots were significantly bigger and heavier than those in the control plots that had natural populations of the biological control agents. This study has shown unequivocally that biological control has contributed significantly to the control of water hyacinth on the Nseleni/Mposa River system.The management plan for the Enseleni Nature Reserve identifies the need to control invasive and/or exotic organisms within the boundary of the protected area. In addition, set guidelines have been implemented on how to control these organisms, so that indigenous organisms are least affected. Lack of control of exotic organisms can have serious consequences for indigenous species. It is therefore of utmost importance that the population dynamics of the invading organism be understood, what the potential impact could be and how to control them. Furthermore, it has also acknowledged the threat of possible exotic species invasions from outside of the protected area that might result in threats to the protected area and that these must be investigated, researched and managed.This thesis has identified Tarebia granifera, Pterygoplichthys disjunctivus and Eichhornia crassipes as being a threat to indigenous biodiversity within the protected area, as well as in adjacent areas to the protected area. The thesis will therefore investigate the hypothesis that both Tarebia granifera and Pterygoplichthys disjunctivus are having a direct negative effect on available food resources for indigenous species of organisms. In addition, this thesis will investigate if theNeochetina species that have previously been introduced onto E. crassipes are having any negative effect on this invasive alien aquatic plant.

The potential role of sanctuary areas for biological control of Schistosomiasis and development of sustainable fisheries was investigated at Cape Maclear, Lake Malawi National Park (LMNP). There has been a recent increase in the incidence of schistosomiasis infection which is a threat to the local community as well as the tourism industry which is the major source of income to LMNP as well as Chembe Village. At the same place there is increasing fishing pressure due to growing human population and declining fish resource. The increase in the incidence of schistosomiasis transmission was attributed in part to over-fishing of the molluscivorous fish which are believed to control the vector snails for schistosomiasis. Four molluscivorous fish species, Trematocranus placodon; Trematocranus microstoma; Mylochromis sphaerodon and Mylochromis anaphyrmus were reported to account for more than 90% of the fishes (by numerical abundance) which feed on the gastropods above 15 metre depth. The gastropod numbers was reported to be highest at 1.5 to 4.5 metre depth. Of the four molluscivores, T. placodon was proposed as a biological control agent for schistosomiasis based upon the previous observations of its feeding habits in artificial conditions. Captive propagation of T. placodon for reintroduction at Cape Maclear in Lake Malawi has been proposed. The present study aimed at providing baseline data required to test the hypotheses that: 1) Over-fishing of the molluscivorous fish has resulted to the increased incidence of schistosomiasis at Cape Maclear. A sub hypothesis to this was that an extension of the LMNP can act as a sanctuary area for the biological control of schistosomiasis by protecting molluscivorous fish which could control schistosomiasis vector snails. 2) A park initially designed to protect the colourful rock dwelling fish and for promotion of tourism may not effectively protect the food fish. To test the first hypothesis, the biology and ecology of T. placodon were investigated with a view to evaluating the effect this species could have on the schistosomiasis vector snail population and hence the control of bilharzia in the lake. The proportions of various gastropod species at Cape Maclear was compared with those found in T. placodon guts. Comparisons of T. placodon abundance and demographic structure inside and outside LMNP were made. To test the second hypothesis, this study investigated the food fish species that use LMNP 100 m protected zone and some basic ecological factors to appreciate the extent to which the adjacent fishery might benefit from their use of the park waters. T. placodon numerical abundance (number of individuals per unit area) ranged from 5.7 to 40.5 /200 m² and it significantly (P< 0.05) varied between sampling sites. Otter Point and Mitande which are inside the park had the lowest abundance as compared to the other three sites; Nguli inside the park; Fisheries and Nchenga outside the park. Two sites in the park, Otter Point and Mitande, had a greater proportion of mature T. placodon individuals than all other sites. The abundance of T. placodon fluctuated significantly from month to month at Nchenga, Nguli and Fisheries (X² test, P<0.0001 for all the three sites) and insignificantly (P>0.05) at Otter Point and Mitande (X² test). T. placodon densities found in the present study corresponded to the peak density of 30 individuals / 200 m² reported in 1986 but did not correspond to that of 1.0 / 200 m² for 1994. There was no evidence to support the previous reports that T. placodon abundance had decreased tremendously from 1986. The reason suggested to account for the discrepancies of T. placodon abundance reported in the present study and other studies was inadequate sampling in the previous studies which did not take into account spatial and temporal variability in T. placodon abundance. The findings reported in this thesis show that there is no need for captive propagation of T. placodon to be reintroduced into the lake at Cape Maclear and that it may prove to be unsuccessful. However, since juvenile T. placodon dominated in abundance at the three sites along the major beach which is outside the park boundaries, it is suggested that the park boundaries be extended to this area so that T. placodon should be protected to allow individuals to grow to bigger size which would be more effective for gastropod control. T. placodon between 60 mm and 80 mm TL fed on benthic insects, phytoplankton and from detritus material. Individuals between 80 mm and 100 mm fed on a mixture of benthic insects, fish scales and small gastropods and at sizes greater than 100 mm individuals specialized feeding on gastropods. Gastropods of five genera were taken and they were: Melanoides , Bulinus, Gabiella, Lanistes and Bellamya. Of these genera Melanoides fonned the greatest part of T. placodon diet. Bulinus was the second most abundant genus but compared to Melanoides its proportion was very small. Of the three Bulinus species taken by T. placodon, B. globosus, is a confirmed vector for Schistosoma haematobium which is prevalent at Cape Maclear. This species was eaten in the least quantities. A comparison ofthe five gastropod proportions in T. placodon diet and in the habitats they occupy showed that Melanoides were taken in proportionately more quantities than Bulinus at most sites. These findings contrasted the previous reports that T. placodon preferred Bulinus to Melanoides. By applying the optimal foraging theory which predicts that an animal species searching for food will go for the type of prey with the highest profitability, it is concluded that the Bulinus cannot be eliminated completely by molluscivores because if their population size falls below a certain level, the fish will switch to other gastropod types. It is concluded that the increase in schistosomiasis may not be necessarily due to overfishing the molluscivorous fish but could be due to the fact that there has been an increase in the proportion of the B. globosus albeit in small numbers which are infected with schistosomiasis parasites. An integrated approach to schistosomiasis control at Cape Maclear comprising vector control, improved water supply, sanitation and health education is suggested since no method can be effective in isolation. Few food fish species were observed to use the park at various times, varying from one species to another with regards to duration, life history stages and abundance. Only a few fish species taken by the adjacent artisanal and commercial fisheries were represented among those observed in the park. This was attributed to the limited diversity of habitat types covered. Only small population size of some species visited the protected area and only part of the life cycle of some species were observed in the park. The use of the park area was seasonal for some species and the protected zone boundaries can be crossed more than once within a day because 100 m distance is just a few minutes swim by fish. Under such circumstances the park cannot function as an effective sanctuary for food fish. An increase of the park size may be a better option to effectively protect the food fish.

O consumo de moluscos bivalves pode representar sérios riscos à saúde pública, pois refletem diretamente as condições do meio ambiente. Desta forma considera-se de extrema importância o consumo de mexilhões livres de contaminação. Esta pesquisa objetivou estudar a qualidade microbiológica das águas e mexilhões de três pontos de cultivo do município de Ubatuba, SP, a saber: Engenho da Almada, Barra Seca e Costão do Cedro em um período compreendido entre novembro de 2002 e março de 2003, totalizando 5 coletas mensais. Analisou-se na água: Bacillus cereus, Clostrídios Sulfito Redutores, Aeróbios Mesófilos, Staphylococcus aureus, Coliformes totais e fecais, Enterococos e Salmonella. Nos mexilhões foram analisados os mesmos microrganismos citados para água mais o Clostridium perfringens. Os resultados encontrados tanto para as análises de água como dos mexilhões foram satisfatórios, condizentes com a legislação brasileira em vigor, salvo a coleta do mês de março, do cultivo da Barra Seca, onde a média dos valores encontrados para coliformes fecais na água (5,7x101 NMP/100mL) foi superior ao recomendado pela legislação sendo detectado também neste mesmo cultivo e mês, presença de Salmonella em 25 g nas amostras de mexilhões. Mesmo que as contagens de S. aureus e B. cereus na carne estejam de acordo com a legislação em vigor, cuidados devem ser tomados quanto ao armazenamento e a forma de consumo. Averiguou-se a intensidade de interferências sazonais na contagem microbiana na água e constatou-se que a tábua de marés e o índice de insolação diária tiveram uma correlação negativa baixa, ao contrário do índice pluviométrico que apresentou correlação positiva alta.<br>The consumption of bivalve mollusks can represent serious risks to the public health, because they reflect the conditions of the environment directly. This way it is considered of extreme importance the consumption of mussels without contamination. This work aims of studing the water and mussels microbiology quality from three different seafood farms in Ubatuba, SP, to know: Engenho da Almada, Barra Seca and Costão do Cedro from November 2002 to March 2003, totaling five monthly. It was analyzed in the water: Bacillus cereus, Total Clostridia, Aerobic Mesophilic, Staphylococcus aureus, total and fecal coliforms, Enterococci and Salmonella. In the mussels the same microorganisms were analyzed mentioned for water more Clostridium perfringens. The results found in the water and in the mussels were satisfactory, suitable with the Brazilian legislation, except for the sample at Barra Seca’s beach, in March. The average of the values found at that place for fecal coliformes in the water was higher (5,7x101 MPN/100mL) than the recommended by the legislation. Even in this collection, it was also detected Salmonella in 25 g of mussels. Even if the counts of S. aureus and B. cereus in the mussesls are in agreement with the legislation in vigor cares they should be taken with relationship to the storage and the consumption form. The intensity of seasonal interferences was discovered in the microbial count in the water, in which was verified that the board of tides and the index of daily heatstroke had a low negative correlation unlike the index pluviometric it presented high positive correlation

Una de les principals limitacions a la que s‘enfronta la producció de mol·luscs bivalves és la prevenció i control de malalties, que es dispersen, principalment, pel moviment d‘estocs. A les Balears, hem trobat paràsits de bivalves poc patogènics com Bucephalus haimeanus, Mytilicola intestinalis, i metacercàries de tremàtodes. També altres que suposen un risc per a la producció, com Marteilia refringens, Perkinsus mediterraneus i P. olseni. La presència de M. refringens és una greu amenaça, doncs produeix desordres fisiològics que poden matar l‘hoste. Probablement, als anys 80, la desaparició dels bancs ostrícoles va ser causada per aquesta malaltia. Els musclos també són susceptibles a la infecció per M. refringens, però són resistents a la malaltia. L‘any 2004, es va detectar una mortalitat al banc de la rossellona (Chamelea gallina) de s‘Arenal de Palma de Mallorca. Per detectar l‘espècie causant de la malaltia es va recórrer a tècniques histològiques, hibridació in situ, PCR i PCR niada. La seqüència obtinguda a partir d‘un bloc de parafina va mostrar un 99,1 % de similitud amb les M. refringens tipus O. D‘aquesta manera es va concloure que l‘agent etiològic era M. refringens i posteriorment que la prevalença era del 55,1%. La ubicació específica de les cèl·lules de Marteilia refringens en els teixits de la rossellona es va determinar per hibridació in situ, trobant totes les fases conegudes, inclosa la d‘esporulació, el que demostra que el paràsit completa la infecció a la rossellona. Perkinsus mediterraneus infecta a una gran varietat de mol·luscs bivalves a l‘arxipèlag balear: Ostrea edulis, Mimachlamys varia, Arca noae, Chamelea gallina, Pinna nobilis i Venus verrucosa, sense mortalitats associades a aquest paràsit. Perkinus olseni sols s‘ha detectat en V. verrucosa, però en el present estudi no l‘hem trobat. La recerca de Perkinsus spp. s‘ha realitzat mitjançant RFTM i la determinació de l‘espècie per PCR-RFLP i seqüenciació. La prevalença de P. mediterraneus ha estat semblant a la d‘altres espècies de Perkinsus i la dinàmica de la seva infecció es semblant a la de P. marinus en la badia de Chesapeake, amb valors màxims de detecció del paràsit al setembre i octubre, després del màxim estival de temperatura, i regressió de la infecció a l‘hivern. Hem trobat 12 haplotips de P. mediterraneus amb una elevada similitud genètica. Les diferències es fan majors en incloure seqüències procedents de la bases de dades del GenBank, augmentant el nombre d‘haplotips a 24. Les anàlisis filogenètiques han detectat, en conjunt, tres grups diferents d‘O. edulis de Menorca, que es diferencien d‘altres llinatges coespecífics. Les anàlisis recolzen aquesta diferenciació entre les poblacions de Menorca i Mallorca, la qual sembla, en bona part deguda a l‘aïllament geogràfic del port de Maó. Malgrat això, altres factors, com la variabilitat ambiental, diferents localitats i dates de detecció, la translocació d‘animals, l‘activitat humana, etc, poden tenir certa influència. Al Mediterrani occidental es troben tres espècies de Perkinsus. Malgrat que es coneix que es produeixen co-infeccions a l‘escopinya gravada del port de Maó amb P. olseni i P. mediterraneus, no hem trobat cap cas, ni tampoc bivalves afectats per P. chesapeaki, espècie que s'ha trobat al delta de l'Ebre. A diferents mostreigs de C. gallina hem detectat la presència de M. refringens i P. mediterraneus. Encara que no hem trobat co-infecció, aquesta no es pot descartar, perquè els individus són molt joves i possiblement ambdós patògens estiguin a fases inicials d‘infecció.Tenint en compte que l‘esporulació de M. refringens s‘inicia quan la temperatura de l‘aigua és de 17ºC (mes de maig), que les zoospores de P. mediterraneus apareixen més tard (setembre-octubre) i que les mortalitats es detecten al juny-juliol, és més probable que la causa de la mortalitat sigui la marteiliosi.<br>Una de las principales limitaciones a la que se enfrenta la producción de moluscos bivalvos es la prevención y control de enfermedades, dispersadas, principalmente, por movimiento de partidas. En las Baleares, hemos encontrado parásitos de bivalvos poco patogénicos como Bucephalus haimeanus, Mytilicola intestinalis y metacercarias de tremátodos. También otros que suponen un riesgo para la producción, como Marteilia refringens, Perkinsus mediterraneus y P. olseni. La presencia de M. refringens es una grave amenaza, pues produce desórdenes fisiológicos que pueden matar al huésped. Probablemente, en los años 80, la desaparición de los bancos ostrícolas fue causada por esta enfermedad. Los mejillones también són susceptibles a la infección por M. refringens, pero són resistentes a la enfermedad. En 2004, se detectó una mortalidad en el banco de la chirla (Chamelea gallina) de s‘Arenal de Palma de Mallorca. Para detectar la especie causante de la enfermedad se recurrió a técnicas histológicas, hibridación in situ, PCR y PCR anidada. La secuencia obtenida a partir de un bloque de parafina mostró un 99,1% de similitud con M. refringens tipo O. De esta manera se concluyó que el agente etiológico era M. refringens y posteriormente, que la prevalencia era del 55,1%. La ubicación específica de las células de Marteilia refringens en los tejidos de la chirla se determinó por hibridación in situ, encontrando todas las fases conocidas, incluida la de esporulación, lo que demuestra que el parásito completa la infección en la chirla. Perkinsus mediterraneus infecta a una gran variedad de moluscos bivalvos en el archipiélago balear: Ostrea edulis, Mimachlamys varia, Arca noae, Chamelea gallina, Pinna nobilis y Venus verrucosa, sin mortalidades asociadas a este parásito. Perkinsus olseni sólo se ha detectado en V. verrucosa, pero en el presente estudio no lo hemos encontrado. La búsqueda de Perkinsus spp. se ha realizado mediante RFTM y la determinación de la especie por PCR-RFLP y secuenciación. La prevalencia de P. mediterraneus ha sido similar a la de otras especies de Perkinsus y la dinámica de su infección es similar a la de P. marinus en la bahía de Chesapeake, con valores máximos de detección del parásito en septiembre y octubre, después del máximo estival de temperatura, y regresión de la infección en invierno. Hemos encontrado 12 haplotipos de P. mediterraneus con una elevada similitud genética. Las diferencias se hacen mayores al incluir secuencias procedentes de la bases de datos del GenBank, aumentando el número de haplotipos a 24. Los análisis filogenéticos han detectado, en conjunto, tres grupos diferentes de O. edulis de Menorca, que se diferencian de otros linajes coespecíficos. Los análisis apoyan esta diferenciación entre las poblaciones de Menorca y Mallorca, la cual parece, en buena parte debida al aislamiento geográfico del puerto de Mahón. Sin embargo, otros factores, como la variabilidad ambiental, diferentes localidades y fechas de detección, la translocación de animales, la actividad humana, etc, pueden tener cierta influencia. En el Mediterráneo occidental se encuentran tres especies de Perkinsus. Aunque se conoce que se producen coinfecciones en la escupiña grabada del puerto de Mahón con P. olseni y P. mediterraneus, no hemos encontrado ningún caso, ni tampoco bivalvos afectados por P. chesapeaki, especie que se ha detectado en el delta del Ebro. En diferentes muestreos de C. gallina hemos detectado la presencia de M. refringens y P. mediterraneus. Aunque no hemos encontrado coinfección, ésta no se puede descartar, porque los individuos són muy jóvenes y posiblemente ambos patógenos estén en las fases iniciales de infección. Teniendo en cuenta que la esporulación de M. refringens se inicia cuando la temperatura del agua es de 17ºC (mes de mayo), que las zoosporas de P. mediterraneus aparecen más tarde (septiembre-octubre) y que la mortalidad se detecta en junio-julio, lo más probable es que la causa sea la marteiliosis<br>One of the main issues in bivalve mollusc production is the prevention and control of diseases, scattered mainly by stock movements. In the Balearic Islands, we found low pathogenic bivalve parasites as Bucephalus haimeanus, Mytilicola intestinalis and trematode metacercariae. Furthermore, we found others that are a threat for their welfare, like Marteilia refringens, Perkinsus mediterraneus and P. olseni. M. refringens is a serious threat, because it causes physiological disorders that could kill the host. Presumably, in the 80s, this disease was the agent of oyster banks die out. Mussels are susceptible to the infection, but they are resistant to the disease. Mass mortality was detected in 2004 at the striped Venus shell (Chamelea gallina) bed in S‘Arenal beach. We use histological techniques, in situ hybridization, PCR and nested PCR to detect the disease agent. From a paraffin block we retrieved a sequence which showed 99.1% similarity with M. refringens type O. Thus, it was concluded that the aetiological agent was M. refringens. Subsequently, we found a prevalence of 55.1%. Marteilia refringens specific location in striped Venus shell tissues was determined by in situ hybridization. We observed all known stages, including sporulation, thus this parasite could complete its vital cycle in C. gallina, and so striped Venus shell should be considered as a new host of M. refringens. A wide bivalve mollusc variety is infected by Perkinsus mediterraneus in Balearic Islands: Ostrea edulis, Mimachlamys varia, Arca noae, Chamelea gallina, Pinna nobilis and Venus verrucosa, but they are not killed by this parasite. Perkinsus olseni has only been detected in V. verrucosa from Mahon harbour, although we have not detected it in another bivalve species. Perkinsus spp. search was performed using RFTM and species was established by PCR-RFLP and sequencing. P. mediterraneus prevalence was similar to other Perkinsus species and their infection dynamics is like P. marinus’ in Chesapeake Bay, with maximum detection values in September and October, after summer peak temperature with infection regression in winter. We have found 12 P. mediterraneus haplotypes, all of them sharing a high similarity. Differences grow up when we added GenBank sequences. Then, the haplotype number raised 24. Three groups of O. edulis from Minorca were revealed by phylogenetic analyses which are different from other co-specifics lineages. Analysis supported this differentiation among populations from Minorca and Majorca. This differentiation could be due to Mahon harbour geographic isolation. Nevertheless, another factors, such environmental variability, different detection locations and dates, animal translocations, human activity, etc., might also have some influence. There are three Perkinsus species at the western Mediterranean. Although it is known that co-infections between P. olseni and P. mediterraneus can happen in warty Venus shell from Mahon harbour, we have not found any occurrence. Furthermore, we have not detected infection by P. chesapeaki, although it has been found in the Ebro delta. We have found out M. refringens and P. mediterraneus presence in different C. gallina samples. Although coinfection has not been found, we cannot discard it, because individuals are very young and perhaps both pathogens are in early infection stages. Given that M. refringens sporulation starts when water temperature is 17ºC (May), P. mediterraneus zoospores appear later (September-October) and mortality is detected in June-July, in this way, marteiliosis might be the candidate.