CHEMTAX-derived phytoplankton community structure associated with temperature fronts in the northeastern Arabian Sea

Remotely sensed sea surface temperature (SST) and chlorophyll associated with fronts and filaments are used in India to generate potential fishing zone (PFZ) advisories in the north eastern Arabian Sea (NEAS). However, biological response to this potential nutrient enhancement has not been investigated. Here we present phytoplankton pigment signatures and nutrient distribution from a section that sampled across a filament and front in the NEAS. We show that nutrient concentrations were high within the filament and front compared to the surrounding waters and had a unique phytoplankton assemblage. Even though there was difference in the physical properties between the filament and front, chemical taxonomy (CHEMTAX) showed dominance of similar phytoplankton groups (prymnesiophytes and prasinophytes). In contrast, Prochlorococcus sp. contributed more than 50% to the total phytoplankton biomass in the surrounding waters and below the oxycline. In general, prymnesiophytes were ubiquitous, covarying with high nutrients and cold temperature, and contributed 60-70% to the total phytoplankton biomass. This study demonstrates that phytoplankton groups respond strongly to nutrient enhancement that is often encountered within the vicinity of the SST fronts that characterize the PFZs.