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

Meio- and macrofauna density and biomass were estimated at the OMEX-transect across the continental slope of the Goban Spur at water depths ranging from 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 found. At the continental shelf meiofauna densities were similar to 50 times higher than macrofauna densities, whereas in the abyss meiofauna densities were more than 1000 times higher. This change in ratio was due to a significant decrease in macrofauna densities with increasing water depth, whereas the 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 three times higher. Macrofauna biomass was high at similar to 1000 m, due to the 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 fraction (>0.5mm) a linear increase in the ratio between nematodes and macrofauna sensu stricto with depth was found. At the deepest station similar to 20% of the macrofaunal fraction were nematodes, at the shallowest station only similar to 2%. Thus, large nematodes became relatively more important with increasing water depth. Within the macrofauna a decrease in the abundance 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 increasing water depth within either group could be observed, the change in meio:macrofauna ratios along the OMEX- transect merely reflects a change in taxonomic (functional) composition, rather than a change in size. [KEYWORDS: Deep-sea meiobenthos; area ne atlantic;size structure nematodes; sediment; ocean; ecology; spectra; sites