BENTHIC MARINE FAUNA STRUCTURED BY HYDRODYNAMIC PROCESSES AND FOOD AVAILABILITY

Benthic macrofauna was investigated, mainly in clayey silt sediments, on the west and east slopes (65-90 m depth) and at the bottom (similar to 100 m depth) of a trench in the Skagerrak, western Sweden. The wes tern slope is an underwater delta front area with, at least intermitte ntly, strong bottom currents transporting suspended organic and inorga nic particles. In the deeper parts, currents slow down and accumulatio n is extremely high (mean similar to 90 mm . y(-1)). The benthic commu nity on the western slope was dominated by the passive suspension-feed ing brittle star Amphiura filiformis. Its numbers and biomass were muc h larger than recorded in the Skagerrak and the North Sea. Total commu nity abundance and number of species were significantly larger on the western slope than on the eastern. In the deep part of the trench sign ificantly higher abundance and number of species were recorded than on the slopes, Dominant in the deep were the small polychaetes, Heteroma stus filiformis and Paramphinome jeffreysi, both assumed to be sub-sur face deposit feeders. Faunal distribution and richness are discussed i n relation to food availability through advective near-bottom processe s on the western slope, and in relation to accumulation at the bottom of the trench. The extreme densities and biomasses recorded on the wes tern slope suggest that these communities were limited by space rather than by food. In contrast, similar communities characterized by A. fi liformis in the Skagerrak and the North Sea have significantly lower a bundance and biomass, and are therefore thought to be food limited.