High summer abundances of small pelagic copepods at the Antarctic Polar Front - implications for ecosystem dynamics

Within the framework of the SO-JGOFS, we investigated the distribution of small copepods (< 2.0 mm) in relation to the hydrography of the Antarctic Polar Front during summer 1995/96. The community of small copepods was dominated by Oithona similis, followed by Oithona frigida and Ctenocalanus citer. The total abundance of these copepods was extremely high throughout the study area, with peaks of up to 49, 000 ind. m(-3), to which naupliar and early copepodid stages (CI-CIII) contributed a high percentage. The accumulation of such a high standing-stock of small copepods is probably related to retention mechanisms provided by the meandering structure of the frontal system and to the biology of the dominant species Oithona similis, Oithona frigida, and Ctenocalanus citer. Stage distribution and metabolic demand of the dominant species indicate a very active and productive zooplankton community, with high grazing pressure on smaller plankton particles and faecal material, leading to high recycling efficiencies and low export rates due to sinking material. This study gives further support to recent findings that small copepod species and early developmental stages of all species are key components of the plankton food web of the Southern Ocean. (C) 2002 Elsevier Science Ltd. All rights reserved.