Microphytoplankton communities off the Antarctic Peninsula region in austral summer 2010/2011

Abstract

Abstract Microphytoplankton communities in waters near the Antarctic Peninsula were investigated using collections made during two krill harvesting cruises in austral summer 2010/2011. Twenty−five net−haul samples were collected. The species composition was assessed, and the cell abundance was counted with a light microscope. A total of forty−four species were recorded, with diatoms being the most abundant group. The predominant species near the South Shetland Islands (SSIs) were Fragilariopsis kerguelensis, Pseudo−nitzschia lineola and Thalassiothrix antarctica, while Rhizosolenia antennata f. semispina was the most common species near the South Orkney Islands (SOIs). Habitat use was preferentially distributed. The average cell abundance of total phytoplankton was 6.6×1011 cells m−2 with high densities detected at the southwest tip of theAntarctic Peninsula. Cluster analysis clearly illustrated that the microphytoplankton communities were different at the SSIs and SOIs. Correlation analysis was applied to interpret the relationship between phytoplankton distribuion and associated hydrographic conditions. Total phytoplankton abundance showed a significant negative correlation with sea surface salinity (p <0.01). The results implied that the high phytoplankton biomass was supported primarily by suitable physical conditions in the upper water column, i.e., relatively stable, stratified and well−lighted seawaters. Water stability in combination with the depth of the upper mixed layer might be the main factor control− ling the phytoplankton distribution in waters near the Antarctic Peninsula.