Surface zooplankton distribution in the Drake Passage recorded by Continuous Plankton Recorder (CPR) in late austral summer of 2000

We investigated the composition, distribution, and abundance of zooplankton in the Drake Passage in February 2000 using a Continuous Plankton Recorder. Zooplankton abundance varied considerably, between 1 and 1537 individuals/segment (where a segment is 5 nautical miles of surface towing) (mean ± SD = 121.3 ± 200.9). The highest abundances were recorded in the vicinity of the Polar Front (PF). Abundances increased at low latitudes north of the Sub-Antarctic Front (SAF) and decreased northward. A positive correlation was observed between zooplankton abundance and chlorophyll a concentration, reflecting the higher abundance of zooplankton north of the SAF, where higher abundances of phytoplankton were also observed. A total of 21 species/taxa of zooplankton were classified. Small calanoid copepods were found throughout the transect and accounted for 57.5% of total zooplankton abundance, followed by the Cyclopoid copepods Oithona spp. (25.9%) and Calanus simillimus (8.4%). The results of cluster analyses reveal that small calanoid copepods were the most important contributors to the high zooplankton abundance around the PF and north of the SAF in the Drake Passage. We suggest that a change in species composition has occurred since Hardy's descriptions in 1927, from abundant larger copepods and chaetognaths to smaller copepods and other species.