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Trophic relationships between demersal fish and benthic fauna at Hausgarten` (79°N west off Svalbard)

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Citation:
Bergmann, M. , Dannheim, J. and Klages, M. (2006): Trophic relationships between demersal fish and benthic fauna at Hausgarten` (79°N west off Svalbard) , 11th International Deep-Sea Biology Symposium, 9-14 July, Southampton, UK. .
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Abstract:

In 1999, the AWI deep-sea research group established the first and only long-term deep-sea observatory beyond the polar circle, 'Hausgarten' (see Soltwedel et al.). Footage from underwater camera transects has shown that demersal fish largely belonging to the eelpout family (Zoarcidae) constitute an important fraction of the benthic fauna. Despite their numerical abundance, little is known about their biology and functional ecological role.Here, we used baited traps and trawls to sample the demersal ichthyofauna at six stations that constitute the shallower end of the Hausgarten depth transect (1200-3200m). Stomach contents analysis showed that trawled eelpout chiefly fed on small crustaceans (cumaceans, amphipods, isopods) and polychaetes whereas trap-caught fish fed largely on scavenging amphipods.Results from radio stable isotope analysis indicate that starfish (Hymenaster pellucidus, Poraniomorpha cf. tumida, Bathybiaster vexillifer) followed by scavenging amphipods (Eurythenes gryllus) occupied the highest trophic level at most stations (δ15N 11.9-24.6). Fish had an intermediate trophic position (Lycodes spp. δ15N 12.8-13.7), reflecting their preference for macrofaunal invertebrates. The lowest trophic level at different stations was occupied by various taxonomic groups due to differences in the composition of species sampled. Assuming a stepwise δ15N enrichment of 3.8 per trophic level, the benthic food web sampled at stations along the depth gradient ranged from four to six trophic levels. This large figure may be indicative of a complex food web structure caused by intense recycling of nutrients which is characteristic for food-limited deep-sea environments. Food limitation may be even stronger at high latitudes due to reduced primary productivity caused by seasonal ice coverage.

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