| Summary: | The enigmatic fauna of chemosynthesis-based ecosystems (CBEs), i.e. hydrothermal vents, cold seeps and organic falls, has been the subject of intensive research over the last decades. However, there are still many aspects of these ecosystems that are poorly understood. There are many shared families and genera of animals between the different types of CBEs, which shows that there is an evolutionary link between them, but the prevalence of shared species and present-day connectivity between different CBEs is debated. The existence of “intermediate” habitats such as sedimented hydrothermal vents and hydrothermal seeps, led to the suggestion that CBEs should be considered a continuum of reducing conditions, rather than completely distinct phenomena. However, it is not clear which environmental factors are most important in structuring the fauna of CBEs, or what determines the habitat specificity of taxa. Evolutionary studies of CBE-adapted taxa often show a gradual adaptation to more extreme environments, with organic falls or cold seeps serving as evolutionary stepping-stones into the hydrothermal vent habitat. Most of these studies, however, have been focused on symbiotrophic taxa, and the evolutionary role of intermediate habitats has not been assessed in a phylogenetic context. Sampling of CBEs is still patchy and biased, both in terms of geographic regions and habitats, which hampers our understanding of biogeographic patterns. The main objective of this project was to contribute to filling these knowledge gaps by focusing on the annelid fauna of CBEs on the Arctic Mid-Ocean Ridge and in the Nordic Seas. The target taxa were worms in the family Ampharetidae, which are commonly found in all types of CBEs around the world, and Sclerolinum contortum and Nicomache lokii, which are abundant habitat-builders in Arctic CBEs. The project aimed to: 1 – describe the new species of Ampharetidae from Loki’s Castle Vent Field (LCVF), 2 – reconstruct the evolutionary history of Ampharetidae, 3 – assess the relationship ...
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