Abstract
We conducted a species-level study of molluscs associated with a 5-m long carcass of a minke whale at a depth of 125 m in the Kosterfjord (North Sea, Sweden). The whale-fall community was quantitatively compared with the community commonly living in the surrounding soft-bottom sediments. Five years after the deployment of the dead whale at the sea floor, the sediments around the carcass were dominated by the bivalve Thyasira sarsi, which is known to contain endosymbiotic sulphur-oxidizing bacteria, while background sediments were dominated by another thyasirid, T. equalis, less dependent on chemosynthesis for its nutrition. The Kosterfjord samples were further compared at the species level with mollusc abundance data derived from the literature, including samples from different marine settings of the west coast of Sweden (active methane seep, fjords, coastal and open marine environments). The results show high similarity between the Kosterfjord whale-fall community and the community that developed in one of the Swedish fjords (Gullmar Fjord) during hypoxic conditions. This study indicates that at shallow-water whale-falls, the sulphophilic stage of the ecological succession is characterized by generalist chemosynthetic bivalves commonly living in organic-rich, sulphidic environments.
Highlights
In the deep sea, the arrival of a whale carcass generates an organic-rich “island” in an otherwise food-poor deep-sea, supporting a highly specialized and diverse assemblage of animals that exhibit a series of successional stages (Smith & Baco 2003)
During the sulphophilic stage chemosynthetic bacteria - free living or in symbiosis within vesicomyid clams, bathymodiolin mussels and siboglinid tube worms – are at the base of a food web where organic matter is primarily produced by the oxidation of inorganic compounds
Some of these animals are restricted to vertebrate carcasses, such as the gutless bone-eating worm Osedax (Rouse et al 2004, 2011), whilst chemosynthetic taxa are often found at other deep-sea reducing habitats, including hydrothermal vents and hydrocarbon seeps (Smith & Baco 2003, Dubilier et al 2008). As they are not restricted to a specific geological setting, whale falls may have played a keyrole in the dispersal of chemosynthetic fauna among these habitats
Summary
The arrival of a whale carcass generates an organic-rich “island” in an otherwise food-poor deep-sea, supporting a highly specialized and diverse assemblage of animals that exhibit a series of successional stages (Smith & Baco 2003). During the sulphophilic stage chemosynthetic bacteria - free living or in symbiosis within vesicomyid clams, bathymodiolin mussels and siboglinid tube worms – are at the base of a food web where organic matter is primarily produced by the oxidation of inorganic compounds Some of these animals are restricted to vertebrate carcasses, such as the gutless ( heterotrophic) bone-eating worm Osedax (Rouse et al 2004, 2011), whilst chemosynthetic taxa are often found at other deep-sea reducing habitats, including hydrothermal vents and hydrocarbon seeps (Smith & Baco 2003, Dubilier et al 2008). The shelf-depth sea floor has much higher organic carbon content and the organic input from a whale carcass may represent a less significant contribution to nutrient budgets in comparison with the deep sea (Smith 2006)
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