Has the fauna in the deeper parts of the Skagerrack changed?: A comparison of the present amphipod fauna with observations from 1933/37

Abstract

Abstract The amphipod fauna at seven, mostly deep water stations from an investigation of the open Skagerrak in 1933/37, were reinvestigated in 1989/90. The composition of the fauna had changed, and diversity was higher in 1989/90 than in 1933/37. There was a distinct increase both in the number of species per sample, the expected number of species in a standard sample size (E[S]), and in the diversity index H′. In the deeper parts of the Skagerrak (>250m) H′ and E[S] had doubled and tripled respectively. The fauna has changed from being dominated by free-swimming visual predators and surface detritivores, to suspension-feeders and burrowing detritivore amphipods. Twinspan, a numerical clas: sification method, divided the seven sampled sites into three groups based on the composition of the amphipod fauna: l) the deep stations(> 250m) from 1933/37, 2) the deep stations(> 400 m) from 1989/90 and 3) one group composed of the shallowest station (- 130m) from both 1933/37 and 1989/90 plus a transition zone station (- 300 m) from 1989/90. The increase in diversity and changes in species composition suggests that the deeper part of the Skagerrak is in an early stage of enrichment and clear negative effects of anthropogenic contaminants on the amphipod fauna were not found.