Microzooplankton community composition along the Western Antarctic Peninsula

Microzooplankton are an integral part of aquatic food webs, yet compared to macrozooplankton, are understudied in the Southern Ocean. The region along the Western Antarctic Peninsula (WAP) is experiencing rapid climate warming, resulting in declines in sea ice extent and duration, and affecting the marine food web. Microzooplankton community structure along the WAP was analyzed in January 2010 and 2011 as part of the Palmer Antarctica Long-Term Ecological Research project. Whole seawater samples were collected within the top 100 m of the water column along both north-south and coastaloffshore gradients, and major taxa of microzooplankton were quantified using microscopy. Average chlorophyll-a concentrations and microzooplankton biomass were higher in 2011 compared to 2010. Athecate dinoflagellates and aloricate ciliates dominated microzooplankton biomass, and the biomass of most taxonomic groups was higher in the south compared to the north. Specifically, aloricate ciliate and tintinnid biomass increased with increasing latitude, and biomass peaked at several southern, inshore stations – including Marguerite Bay, which was an area of high biomass for some microzooplankton taxa. Biomass was higher in surface waters compared to 100 m, and variability in microzooplankton biomass between years and with distance from shore was most likely due to sea ice dynamics. Microzooplankton biomass was positively correlated with chlorophyll-a and particulate organic carbon. These results are used to consider how microzooplankton populations may be adjusting to environmental changes along