Monitoring variability and change in the plankton communities of the Scotia Sea through Continuous Plankton Recorder surveys

The northern regions of the Scotia Sea demonstrate notable variability in environmental conditions, particularly in the location of the Polar Front. This has a strong influence on patterns of productivity and distribution of plankton, with implications to higher trophic levels, including harvested species. The long-term impact of environmental variability on plankton species composition and abundance has been monitored through conducting a series of Continuous Plankton Recorder (CPR) tows in the South Atlantic Ocean since 2005. The tows were carried out as a collaboration between the British Antarctic Survey (BAS) and the Sir Alister Hardy Foundation for Ocean Science (SAHFOS). This report documents the series of tows that have been carried out to date, which comprises more than 2000 samples from 78 successful tows. Of these, 715 samples have been analysed.  A total of 245 taxa have been recorded, with abundance being far more variable than species composition within and between tows.  In general, phytoplankton were most abundant in the tows taken in November and December but sharp declines occur by April. Diatoms dominated the phytoplankton together with coccolithophores and silicoflagellates. The most commonly recorded copepod was Calanus simillimus, while Thysanoessa spp. was the most abundant euphausiid. An analysis considering the relationship between satellite-derived dynamic height (from which frontal positions may be approximated) and abundance of biomass-dominant species indicated varying affinities, implying that major faunal shifts will accompany any changes to frontal locations in this region.