Increase of benthic biomass in the Skagerrak-Kattegat during the 1970s and 1980s - effects of organic enrichment?

Abstract

Biomass and abundance of macrobenthos was monitored from 1972 to 1988 at 14 soft-sediment stations below the h a l o c h e in the Skagerrak-Kattegat area. Year-to-year variations in fauna were analysed. Clear general trends were demonstrated over the study area, w h c h is > 170 km long. Total biomasses showed linear increases by a median factor of 1.8, primanly from 1981 to 1988. and biornasses excluding some large species, notably echinoids, increased by a median factor of l. ? from 1972 to 1988. The changes were primarily due to echinoderms, notably the amphiurold Amphiura filiformis, and polychaetes. Polychaetes contributed more to the increase at the deepest stations, and the absolute increase of this group was positively related with water depth. The relative increases in 'biomass without large species' as well as biornass of arnphiuroids and polychaetes were positively related to water depth. Parallel to the biornass change, land freshwater runoff from western Sweden and to Danish inner waters have increased, and this has influenced the input of nutrients to the sea. Although rellable data on primary production and sedimentation of organic material are largely lacking. the present results are in accordance with hypotheses that soft-sediment infauna in the area is food limited, and that the area is being affected by organic enrichment. P