Spatiotemporal statistical analyses reveal predator-driven zooplankton fluctuations in the Barents Sea

Abstract

There is limited statistical support for top-down effects on plankton in oceanic ecosystems. We quantify the combined effects of key planktivorous fish, invertebrates and climate on mesozooplankton dynamics in the Barents Sea. Zooplankton biomass was measured during Russian and Norwegian surveys in April–May and June–July 1959–1990 and August–early October (1981) 1984–2010. We found that zooplankton biomass in the central and northern Barents Sea in August–October showed pronounced multi-year fluctuations that were strongly negatively correlated with the total biomass of planktivorous fish. Fish predation explained >50% of the interannual variability in the biomass of medium-sized and large mesozooplankton in these parts of the Barents Sea and the predation effects remained significant while accounting for effects of climate variables. Spatiotemporal statistical analyses for different zooplankton size fractions supported the interpretation of top-down control, predominantly from capelin, on the zooplankton. In the southwestern Barents Sea the fluctuations were less pronounced and uncorrelated to total biomass of planktivorous fish, suggesting weaker top-down control by fish in this region, characterised by higher productivity and higher diversity of the predators. We suggest that predator-driven zooplankton fluctuations may play an important role in the ecosystem dynamics of the Barents Sea and potentially other Arcto-boreal shelves.