Benthic marine fauna structured by hydrodynamic processes and food availability

Abstract

Benthic macrofauna was investigated, mainly in clayey silt sediments, on the west and east slopes (65–90 m depth) and at the bottom (≈100 m depth) of a trench in the Skagerrak, western Sweden. The western slope is an underwater delta front area with, at least intermittently, strong bottom currents transporting suspended organic and inorganic particles. In the deeper parts, currents slow down and accumulation is extremely high (mean ≈90 mm·y⁻¹). The benthic community on the western slope was dominated by the passive suspension-feeding brittle star Amphiura filiformis. Its numbers and biomass were much larger than recorded in the Skagerrak and the North Sea. Total community abundance and number of species were significantly larger on the western slope than on the eastern. In the deep part of the trench significantly higher abundance and number of species were recorded than on the slopes. Dominant in the deep were the small polychaetes, Heteromastus filiformis and Paramphinome jeffreysi, both assumed to be sub-surface deposit feeders.

Faunal distribution and richness are discussed in relation to food availability through advective near-bottom processes on the western slope, and in relation to accumulation at the bottom of the trench. The extreme densities and biomasses recorded on the western slope suggest that these communities were limited by space rather than by food. In contrast, similar communities characterized by A. filiformis in the Skagerrak and the North Sea have significantly lower abundance and biomass, and are therefore thought to be food limited.