Inter-annual variability in abundance and community structure of zooplankton south and north of Iceland in relation to environmental conditions in spring 1990-2007

Abstract

An 18 year zooplankton time series from two standard sections differing in hydrographic conditions (Subarctic Water north of Iceland and Atlantic water south of Iceland) was examined in relation to hydrography and phytoplankton dynamics, and large-scale climatic changes in the North Atlantic Ocean, particularly the North Atlantic Oscillation (NAO). The long-term mean zooplankton abundance was higher in south (∼160 000 individuals m−2) than that in north of Iceland (∼120 000 individuals m−2). Abundance fluctuated markedly between years. Copepods (mainly Calanus finmarchicus and Oithona spp.) dominated the zooplankton, comprising >60–70% of the plankton in most years. Among the copepods, C. finmarchicus was more abundant in south of Iceland (∼20–70%) than to the north (∼10–60%). Abundance and community structure were related to environmental variables using regression and multivariate techniques (principal component analysis and redundancy analysis). Temperature and salinity were the most important environmental variables in explaining the differences in species composition in north and south of Iceland, with species and groups like Podon leuckarti and cirripede larvae being relatively abundant to the south, and C. hyperboreus to the north of Iceland. A significant year-to-year variability in community structure was observed both to the south and to the north, with salinity and used nitrate dictating the variability to the south and temperature to the north (Monte Carlo permutation tests, P < 0.05). In neither region was a unidirectional temporal trend in species composition.