Nanophytoplankton in the Bransfield Strait: Contribution of Cryptophyta to the Community Abundance and Biomass During Austral Summer

Abstract

The chapter describes the flow cytometry data on the abundance and biomass of nanophytoplankton in the central Bransfield Strait, and their distribution across the strait in relation to hydrology and hydrochemistry of the two major water masses: the warmer and less saline Transitional Zonal Water with Bellingshausen Sea influence (TBW), and the cold and salty Transitional Zonal Water with Weddell Sea influence (TWW). Two nanophytoplankton clusters were distinguished and enumerated in the cytograms: larger cells (about 9 μm) of cryptophytes with bright orange fluorescence, and smaller cells (3 μm) of other nanophytoplankton (NP). It was shown that both assemblages develop to higher abundances and biomasses in the warmer and less saltine TBW. This biotope was characterized by a much more diverse nanophytoplankton community with a pronounced dominance of Cryptophyta in terms of biomass. Temperature did not appear to be a key factor controlling NP growth. The results support the idea that the increasing melt-water input can potentially increase the spatial and temporal extent of cryptophytes. The replacement of large diatoms with small cryptophytes leads to a significant shift in trophic processes in favor of the consumers like salps that are able to graze on smaller prey. If this trend persists, the food web shifts will eventually impact biogeochemical cycling in Antarctic coastal waters.