A mass occurrence of pteropods (Limacina spp.) drove a pronounced peak in zooplankton biomass in Atlantic water in the Barents Sea in 1994.

Abstract

Zooplankton have been monitored on autumn cruises in the Barents Sea since the late 1980s. The time series shows a pronounced peak in zooplankton biomass in the inflow region of Atlantic water in 1994. The mean biomass was ~ 20 g dry weight m^-2, which is more than twice the long-term average, and showed an atypical composition with dominance of the small size fraction (<1 mm). Analysis of stored samples revealed that the high biomass event in 1994 was due to a mass occurrence of two species of Limacina pteropods (Limacina retroversa and Limacina helicina) dominated by small juveniles < 1 mm in diameter. High biomass in the Atlantic inflow region also in 1995 was due to a strong but delayed summer generation of the dominant copepod Calanus finmarchicus. Estimated biomass of copepods (from numbers and individual weight by species and stage) was strongly dominated by C. finmarchicus in both years (~90%). The average biomass of Limacina spp. in 1994 was ~ 7 g dw m^-2, estimated to be mainly in the small fraction, and contributed to the 1994 peak on top of a "typical" biomass of C. finmarchicus. The results contribute to a better understanding of the Barents Sea ecosystem.