Periodicity of composition, abundance, and vertical distribution of summer zooplankton (1977/1978) in Ezcurra Inlet, Admiralty Bay (King George Island, South Shetland)

Abstract

Seasonal succession and variation in species composition, density, biomass, age distribution and frequency of zooplankton (mainly the Copepoda) were analysed during the austral summer of of 1977/1978 in Ezcurra Inlet, a part of the Antarctic coastal ecosystem. Small zooplankters (i.e., cyclopoids of the genera Oncaea and Oithona, and calanoids Drepanopus pectinatus and Scolocithricella glacialis) were found to predominate in terms of abundance and percentage contribution. The zooplankton biomass was dominated by larger organisms of the Metrididae and Calanidae (Calanoida). The maximum abundance and maximum biomass of copepods were recorded in February; two small peaks in copepod biomass being observed in late December and late January, and a lesser biomass peak in late December. The vertical distribution of copepods in terms of their diel and seasonal (December, January, February, March) changes showed a day-time maximum to have occurred in the near-bottom layer, the nocturnal distribution being bimodal with peaks within 0–10 m and 25–50 m. The summer zooplankton community in Ezcurra Inlet is controlled by trophic (phytoplankton composition and density) and hydrological (water exchange with Bransfield Strait) conditions prevailing in the area.