Seasonal patterns in diversity and abundance of the High Antarctic meroplankton: Plankton sampling using a Ross Sea desalination plant

Abstract

The Antarctic marine environment is thermally stable, yet shows pronounced seasonality in the light : dark cycle, primary productivity, and the extent of sea-ice cover. Thorson’s Rule, predicting reduced meroplankton diversity at high latitudes, was based on the perceived difficulties in completing larval development at low temperatures and within the short summer period of phytoplankton production. Yet few studies have addressed seasonal patterns in Antarctic meroplankton diversity and abundance, especially in the High Antarctic. Here we circumvented logistical difficulties in conducting winter plankton sampling by using the 100-mm primary filter on the desalination plant at Scott Base in McMurdo Sound, Ross Sea (77u519S), to sample embryos and larvae. Using samples from an entire calendar year we found no seasonal changes in either embryo or larval operational taxonomic unit (OTU) diversity with season, no seasonal changes in embryo abundance (5000 L21), but a peak in larval abundance during the period of the summer phytoplankton bloom (maximum 295 larvae 5000 L21). While some OTUs showed a strong seasonality, there was also a high diversity of both embryos and larvae during the autumn and winter, and some OTUs were present in the meroplankton year-round. Annelids, molluscs, and echinoderms were dominant members of the Ross Sea meroplankton, showing similar prevalence to that seen at Signy (60u439S) and Adelaide Islands (67u34.59S). The use of the desalination plant primary filter allows plankton samples to be collected year-round, even in the High Antarctic with permanent sea-ice and 4 months of 24-h darkness