| Summary: | Whale carcasses reaching the bottom of the ocean, known as “whale falls”, represent massive organic inputs that provide habitat islands for complex communities of specialised fauna. However, studies about these habitats are mostly restricted to the Pacific Ocean. To investigate the importance of whale falls in the deep-Atlantic Ocean, five mammal carcasses were deployed within the CARCACE project at 1000 m depth in the Setubal canyon (NE Atlantic, west Portuguese margin). In order to describe the fauna associated with the carcasses, investigate the trophic ecology of the metazoan assemblages and analyse the functional morphology of the encountered specialists, bones resulting from the degradation of the carcasses were collected 18 and 28 months after the deployment using a ROV. In this context, the colonisation patterns of two dominant taxa of invertebrates found in the colonising assemblages, the mytilid mussel “Idas” simpsoni and Dorvilleidae polychaetes were studied. Regarding “I.” simpsoni the specific goals of this work were to investigate its settlement patterns and to understand its nutritional strategy. The analyses of the populations' size structure showed a continuous settlement and a limitation in growth and adult survival. These limitations are probably due to insufficient energy supplied by the cow bone to maintain chemosynthesis, which is in agreement with the isotopic signatures that indicated a higher contribution of filter feeding than chemosynthesis to their nutrition. Concerning the dorvilleid assemblages, the analyses of species composition disclosed temporal variations associated with distinct food sources at different degradation stages of the bones, as different species presented different isotopic signatures. Moreover, species distribution in different microhabitats did not show any relation with the substrate texture, hardness and presence of conspicuous filamentous bacteria on the surface. The morphology of the jaw apparatus of the different dorvilleid species was also analysed in order to investigate the relationship between this structure and trophic ecology. Dorvilleid jaw apparatuses are generally used in taxonomic and phylogenetic studies, but this is the first study on the functional anatomy of these structures. Species with similar jaw characteristics exhibited similar isotopic signatures, suggesting a possible role of the jaw morphology in the specialisation on different resources. However, further studies, using more species from different habitats, are needed to establish this relationship. Overall, these results give significant insights about the ecology of the studied species and into the colonisation patterns of deep-sea mammal carcasses in the Atlantic Ocean.
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