Assessing long-term changes in early summer zooplankton communities around Iceland

A summary of the Icelandic Spring Survey zooplankton data for May and June is presented for the years 1960-1996, along with time-series information on sea surface temperature. Changes in zooplankton abundance are assessed using displacement volumes and simple index numbers modelled as various functions of temporal (year) and location (latitude and longitude) covariates. Long-term displaced volumes of zooplankton remained fairly stable although there were pronounced short-term fluctuations. Further, the proportion of specimens in each sample belonging to species with affinities of water of Atlantic type has fallen dramatically over the Icelandic Shelf since the 1960s, whereas the proportion of species with Arctic affinities has increased most markedly northeast of Iceland.