Spatio-temporal patterns in diversity of a fish assemblage along the Norwegian Skagerrak coast

Time series from 1953 to 1997 of 34 fish species sampled by beach seine at 69 stations along the Norwegian Skagerrak coast were analysed to describe spatial patterns of temporal variation in species richness and diversity. Principal Components Analyses were performed on species richness, total abundance and the Shannon diversity index. Spatially consistent temporal variation was detected on a scale exceeding that of the individual fjords. Two main spatial patterns were detected: one for the open Skagerrak, which showed large temporal variability with a decrease in the number of species for most of the study period followed by a recovery in the number of species, and another for the Oslofjord area, which did not show a recovery in the number of species. The total abundance and the Shannon diversity index for the same data set failed to reveal these spatial patterns. Underlying processes that might be related to the spatio-temporal variation of the fish assemblage, especially eutrophication and industrial pollution, and climatic changes are discussed.