Zooplankton dynamics in the eastern Atlantic sector of the Southern Ocean during the austral summer 1997/1998—Part 2: Grazing impact

Abstract

Zooplankton grazing impact using the gut fluorescence technique was investigated in the top 200 m water layer along the 6°E meridian between 49°50′ and 60°25′S at six Biostations during a Scandinavian/South African Joint Global Ocean Flux Study (December 1997–January 1998) on board the SA Agulhas. Copepods were found to be the most conspicuous grazers along the entire transect, generally accounting for ≈40% of total zooplankton grazing. Pelagic pteropods, Limacina helicina and Clio sulcata, were the second most important grazers within the Seasonal Ice Edge (SIE) region, while the tunicate Salpa thompsoni and euphausiids, mainly Euphausia superba and E. frigida, were the second and third most important consumers of the phytoplankton production within the Winter Ice Edge (WIE) and Antarctic Polar Front (APF) regions. The overall ingestion rates of the zooplankton community ranged from 24 to 277 mg C m−2 day−1. The lowest and highest ingestion rates were recorded within the SIE and APF regions. The zooplankton grazing impact was low within the SIE region accounting for <10% of daily primary production. The highest phytoplankton consumption rate (56% of daily primary production) was observed in the WIE region, while the APF region was characterized by modest (23–33%) grazing impact of zooplankton.