NEMATODE ASSEMBLAGES OF DEEP-SEA AND SHELF BREAK SITES IN THE NORTH-ATLANTIC AND MEDITERRANEAN-SEA

The nematode community structure of several shelf break and deep-sea s tations in the North Atlantic and the Mediterranean is compared using data from the literature. Samples from 2 Mediterranean deep-sea canyon s have a unique fauna of predatory and scavenging nematodes (e.g. Syno nchiella, Halichoanolaimus, Gammanema) which comprise some 20 to 30% o f the community, while some of the typical deep-sea genera (Theristus, Acantholaimus) are only marginally present. The nematode generic comp osition of the other sites reveals a gentle transition from the shelf break (Bay of Biscay; Mediterranean) over the slope (Mediterranean) to wards the continental rise, abyssal plain and hadal depths (Bay of Bis cay, Puerto Rico Trench, HEBBLE site, Hatteras Abyssal Plain). At all these sites predators and omnivores are less abundant (<10 %), while b acterial feeders (deposit and epistrate feeders) predominate. With inc reasing water depth, the genus Sabatieria becomes less dominant, while the genera Theristus, Acantholaimus and Halalaimus gain in importance . We suggest that this is caused by the growing importance of the oxic mineralization pathway at greater depth, As such the relative amount of organic matter that enters the suboxic and anoxic regions of the se diment diminishes with depth. These anoxic or suboxic regions are typi cally inhabited by Sabatieria. It is argued that larger fluxes of orga nic matter to the bottom in the Mediterranean canyon, compared to the other sites, allow for a higher trophic complexity of the nematode com munities and a higher mean nematode biomass. Trends in nematode biomas s, mean individual weight and nematode density are discussed.