Zooplankton distribution patterns in relation to the Antarctic Polar Front Zones Recorded by Continuous Plankton Recorder (CPR) during 1999/2000 Kaiyo Maru cruise

Abstract

During the 8th Antarctic Expedition of the R/V Kaiyo Maru of the Japan Fisheries Agency, October 1999 to March 2000,a Continuous Plankton Recorder (CPR) was used to investigate zooplankton composition and abundance in the surface of the Indian sector of Southern Ocean between South Africa and Antarctica. Total zooplankton abundance ranged from 0 to 432 individuals/segment (a 5 nautical miles of the surface towing) (Mean±SD=69.7±83.5). Zooplankton abundance tended to be higher in the high latitudes than the Sub-Antarctic Front (SAF). Opposite correlations were observed between zooplankton and seawater temperature (negative), salinity (positive) and in vivo fluorescence value (positive) reflecting the higher abundance of zooplankton found in the cooler waters south of the SAF, which also have higher salinities and phytoplankton. Among twenty-nine species/taxa identified, cyclopoid copepod Oithona spp. were found throughout the transect, and accounted for 53.3% of total zooplankton abundance. Cluster analysis based on seventeen dominant zooplankton species/taxa revealed two groups and three ungrouped individual species/taxa at the 84% dissimilarity level. On the other hand, the cluster analysis based on the samples obtained in a 5 nautical miles indicated two major distinctive zooplankton community groups at 89% dissimilarity level. The main group included most segments in the Polar Frontal Zone (PFZ : region between SAF and the Polar Front) and Antarctic Zone (AZ : south of the Polar Front) with high zooplankton abundance while the second mainly group comprised lower latitude segment with low abundance (<100 individuals/segment)