The meiofauna : macrofauna ratio across the continental slope of the GobanSpur (north-east Atlantic)

Meio- and macrofauna density and biomass were estimated at the OMEX-transec t across the continental slope of the Goban Spur at water depths ranging fr om 208 to 4460 m in the north-east Atlantic. A linear increase in the ratio between meio- and macrofauna densities with increasing water depth was fou nd. At the continental shelf meiofauna densities were similar to 50 times h igher than macrofauna densities, whereas in the abyss meiofauna densities w ere more than 1000 times higher. This change in ratio was due to a signific ant decrease in macrofauna densities with increasing water depth, whereas t he meiofauna densities staved more or less at the same level. The ratio in biomass between meio- and macrofauna showed a dip at similar to 1000 m. At this depth macrofauna biomass was similar to 55 times higher than meiofauna biomass, whereas at similar to 4500m macrofauna biomass was only about thr ee times higher. Macrofauna biomass was high at similar to 1000 m, due to t he high mean individual weight of the macrofauna, whereas meiofauna biomass and mean individual weight were low at this depth. Meiofauna consisted of similar to 90% nematodes. Within the macrofaunal fra ction (>0.5mm) a linear increase in the ratio between nematodes and macrofa una sensu stricto with depth was found. At the deepest station similar to 2 0% of the macrofaunal fraction were nematodes, at the shallowest station on ly similar to 2%. Thus, large nematodes became relatively more important wi th increasing water depth. Within the macrofauna a decrease in the abundanc e of filter- and surface deposit-feeders relative to the subsurface deposit -feeders with increasing water depth was observed, which may be related to a change in food input. As no decrease in mean individual weight with incre asing water depth within either group could be observed, the change in meio :macrofauna ratios along the OMEX-transect merely reflects a change in taxo nomic (functional) composition, rather than a change in size.