Macrozooplankton communities and environmental variables in the Barents Sea marginal ice zone in late winter and spring

Abstract

The horizontal distribution of macrozooplankton (≥3 mm) was studied with respect to changes in environmental conditions along 3 transects across the marginal ice zone (MIZ) in the NW Barents Sea during late winter (March 2000) and spring (May 1999). The water masses, which were identified by their salinity and temperature characteristics, largely determined the macrozooplank- ton composition, but season (late winter vs spring), geographical area (latitude and longitude) and bottom depth were also important. Almost 80% of the total macrozooplankton variability could be explained by changes in these environmental variables. Ice cover and the algal bloom situation had no significant impact on the horizontal macrozooplankton distribution early in the season (March to May). We sampled 3 main water masses: cold and less saline Arctic water (ArW), warm and saline Atlantic water (AtW) and mixtures of these (MIX); 5 distinct macrozooplankton communities were found, 2 in ArW (ArW bank and ArW slope), 2 in MIX (warm, >1°C, and cold, <0°C, MIX) and 1 in AtW. These communities were characterised by differences in species abundance rather than differ- ences in taxonomic composition. Numerically important macrozooplankton were Calanus glacialis, C. hyperboreus, Thysanoessa inermis and Aglantha digitale. These were also important in terms of wet biomass together with Beroe cucumis, Clione limacina and Sagitta elegans. Good indicator species for ArW were C. glacialis, C. limacina, Mertensia ovum and Parathemisto libellulla, and for AtW Thysanoessa spp. (T. inermis, T. longicaudata and T. raschii). Characteristic for MIX, i.e. the Polar Front region, was low macrozooplankton abundance, biomass and species richness compared to AtW and ArW. Seasonal variability (late winter vs spring) accounted for 21% of the total macro- zooplankton variability. Particularly the herbivores showed large seasonal variability in abundance and biomass, most probably due to their seasonal migration patterns.