Intra-annual seasonal variability of surface zooplankton distribution patterns along a 110°E transect of the Southern Ocean in the austral summer of 2011/12

Seasonal cycles can provide insight into the interactions between zooplankton and the environment. However, few intra-annual seasonal studies have been undertaken in the Southern Ocean. We investigated the composition, distribution, and abundance of micro- and meso-zooplankton along the 110°E meridian with three transects in December 2011, January and March 2012 using a Continuous Plankton Recorder. High zooplankton abundance was recorded in the Polar Frontal Zone (PFZ) and the Antarctic Zone (AZ) in both day and night at all transects with 179.0–300.9 ind. m−3. The small copepods Oithona similis, Ctenocalanus citer, and copepodites indet (copepod indeterminable) were dominant in the PFZ and AZ communities. Total zooplankton abundance was comparatively consistent among transects. Nighttime abundance levels remained high in the AZ in March with high abundance of copepodites indet. This seasonal fluctuation appeared to be influenced by recruitment of new populations. Most core species/taxa, except for O. similis, C. citer, and foraminiferans in the AZ area in early January, exhibited a diel decrease in abundance. A multi-ship intra-annual seasonal survey will help detect their various regional and/or seasonal distribution patterns, and the impacts of environmental change on Southern Ocean pelagic ecosystems.