Nematode biomass and morphometric attributes as biological indicators of local environmental conditions in Arctic fjords

Kongsfjord and Hornsund are fjords located on the west coast of the island of Spitsbergen that differ in terms of hydrographical conditions and food source availability for benthic organisms. We studied the nematode communities of these two glacial fjords with respect to their morphometric attributes (body length, width, length/width ratio) and biomass (total and individual) to evaluate whether their differences reflect differences in hydrographical and biogeochemical conditions. Sediments collected from Kongsfjord, which contained enhanced marine organic material than sediments from Hornsund, supported nematode communities exhibiting higher biomass and morphological diversity. The roles that the biochemical properties of sediments and food availability play in structuring biological communities were reflected in the wider spectrum of length/width ratio (L/W) and size spectra, with biomass dominance in the higher weight-classes observed in Kongsfjord. In this respect, the appearance of short and plump nematodes in the Kongsfjord nematode assemblage (12% of all nematodes), characterised by a L/W ratio of <12, was striking. This morphotype, which is almost absent in the Hornsund fjord (4%), is considered to be an indicator of well-oxygenated sediments with favourable food sources and may further confirm that the organic material in the Kongsfjord sediments is of higher quality. Furthermore, the homogeneity of sediment composition suggests that the morphological landscape of nematode communities are not structured by granulometry per se, as has been suggested in other studies, but rather by other environmental factors that are indirectly connected with particle size. The results of the present study provide evidence that the morphometric characteristics of nematodes are suitable for detecting differences in sediments, particularly with regard to organic matter availability.