Deep-sea nematode diversity and ecosystem function

Biogeosciences Discussions This discussion paper is/has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG if available. Abstract Alongside a primary productivity gradient between the Galicia Bank region in the northeast Atlantic and the more oligotrophic eastern Mediterranean basin, we investigated the bathymetric (1200–3000 m) and longitudinal variation in several measures for nematode taxon (Shannon–Wiener genus diversity, expected genus richness and generic 5 evenness) and functional diversity (trophic diversity, diversity of life history strategies, biomass diversity and phylogenetic diversity). Our goals were to establish the form of the relation between diversity and productivity (measured as seafloor particulate organic carbon or POC flux), and to verify the positive and negative effect of sediment particle size diversity (SED) and the seasonality in POC flux (SVI), respectively, 10 as observed for other oceanographic regions and taxa. In addition, we hypothesized that higher taxon diversity is associated with higher functional diversity, which in turn stimulates carbon remineralisation rates by nematode assemblages (determined from biomass-dependent respiration estimates). Taxon diversity showed a positive linear relationship with seafloor POC flux. Both SED (against our expectations) and SVI (as ex-15 pected) had a negative influence on several nematode diversity indices. We observed a positive linear relation between taxon diversity and carbon remineralisation, but none of the functional diversity indices computed in the present study provided a mechanism through which taxon diversity may promote this ecosystem function. The present results suggest potential repercussions of climate change on deep-sea ecosystem func-20 tioning, but further also emphasize the need for a better understanding of nematode functions and their response to evolutionary processes.