Mollusc fauna along an offshore-fjord gradient

Abstract

From along a transect from the Norwegian Trough to the inner parts of a fjord system, the Shannon-Wiener diversity of 65 mollusc species decreased markedly from offshore to the innermost stations; there were fewer but more abundant species in the fjords than offshore. Diversity was positively correlated to sill depth, and negatively correlated to distance to "species pool' (=recruitment area), C/N, and % carbon in the surface sediment, TWINSPAN divided the mollusc fauna into offshore, outer fjord, and inner fjord faunas. The environmental variables that explained most of the variance between species were still depth, distance to "species pool', C/N, %C, % loss on ignition, and median phi-size, and together accounted for 74% of the variance in the species data. The diversity of the deep fjord fauna of molluscs and amphipods is low compared to adjacent offshore areas, because the sediment habitat (food resources, measured as C/N, and grain size) may be more diverse offshore than in fjords, or the higher influx of organic matter in fjords may favour dominance of a few opportunistic species. -from Authors