Surface zooplankton communities in the Indian sector of the Antarctic Ocean in early summer 1999/2000 observed with a Continuous Plankton Recorder

Abstract

The first deployment of a Continuous Plankton Recorder (CPR) on board the icebreaker Shirase was conducted during the 41st Japanese Antarctic Research Expedition (JARE) in 1999/2000 austral summer in the Indian sector of the Antarctic Ocean. The CPR was towed horizontally at approximately 10m depth while the Shirase was steaming at about 14 knots across the Polar Front (PF). Mean total abundance of zooplankton for horizontal five nautical mile sample units was 168.1(SD : ±117.18) individuals with the maximum of 456 individuals. Zooplanktons were counted for 34 categories of species/taxa. Copepods occupied more than 90% of the total abundance in numbers. Oithona spp. was the most dominant group among copepods, representing 59% of the total zooplankton. Other numerically important categories were small-sized calanoids (copepodites and adults; 18.4%), and copepodites of Calanoides acutus and Calanus simillimus (8.2%). Latitudinal change of zooplankton abundance coincided with increasing/decreasing tends of temperature and salinity. Two different zooplankton assemblages were identified by cluster analysis and these assemblages seem to be closely related to different water characteristics, such as the of PF and areas of cold water masses. CPR is considered to be an ideal tool for long term monitoring of surface zooplankton communities.