Large-scale variation in macrofaunal communities along the eastern Nordic Seas continental margin: A comparison of four stations with contrasting food supply |
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| Authors: | Mark A Shields David J Hughes |
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| Institution: | aScottish Association for Marine Science, Dunstaffnage Marine Laboratory, UHI Millennium Institute, Oban, Argyll PA37 1QA, Scotland, United Kingdom |
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| Abstract: | A hypothesis-driven approach was used to examine the relative importance of pelagic and advective organic flux as drivers of macrofaunal community structure at mid-slope (900–1400 m) depths along the eastern Nordic Seas margin. Ice-free stations were sampled on the Vøring Plateau (VP, mainly pelagic flux) and Bear Island Fan (BIF, major downslope advection). Seasonally ice-covered stations with episodic inputs of fresh phytodetritus were located on the Svalbard Margin (SM, major current-driven advective input), and Yermak Plateau (YP, low advective input). Macrofaunal biomass was higher at stations with seasonal ice cover, suggesting a greater supply of bioavailable organic matter in the marginal ice zones. At VP, BIF and SM, box corer and multiple corer samples gave broadly consistent community data. Very large infauna in box corer samples from YP indicated the existence of a faunal component absent or not sampled at the other three stations. This faunal component and higher mean body size for 18 out of 23 major taxa at YP relative to VP was consistent with a hypothesis relating body size to interannual variability of sinking flux, but was confounded by a depth difference between the two stations. Consistent with predictions, taxa associated with subsurface ‘caching’ of fresh organic matter were important community elements at stations experiencing episodic pelagic input, but not at the advection-dominated BIF. Current-driven advective flux was associated with high suspension-feeder biomass at BIF, but not at SM. The predicted high representation of subsurface deposit-feeders at BIF was not found. Sipunculans (Nephasoma sp.) known to rapidly subduct fresh organic matter were found at all stations but were most abundant at VP. Comparison with data from the mid-1980s showed a large difference in estimated macrofaunal abundance on the Vøring Plateau, but good agreement in biomass. Community patterns on the Vøring Plateau were generally consistent with earlier data. Standing stock estimates from the Svalbard Margin and Yermak Plateau also agreed well with previous data. Results suggest that large-scale contrasts in organic flux can be used to predict some aspects of bathyal macrofaunal community composition in the Nordic Seas. |
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