Variability of phytoplankton biomass and environmental drivers in a semi-enclosed coastal ecosystem (San Matías Gulf, Patagonian Continental Shelf, Argentina) using ocean color remote sensing (MODIS) and oceanographic field data: Implications for fishery resources

Abstract

Annual cycles of phytoplankton biomass (using chlorophyll-a as a proxy) and seasonal patterns of environmental drivers were analyzed in a semi-enclosed coastal ecosystem (San Matías Gulf, SMG, Patagonian Continental Shelf, Argentina). Monthly climatologies (2003-2014) of satellite images of chlorophyll-a (Chla-sat), sea surface temperature (SST), photosynthetically available radiation (PAR), and euphotic depth (Z1%) were analyzed using Principal Component Analysis (PCA). Satellite environmental variables were evaluated together with oceanographic field data (temperature, nitrate, and chlorophyll-a). Thus, this study analyzes the Chla-sat data to describe the spatio-temporal distribution of the phytoplankton biomass in the SMG and investigates its relationship with the regional environmental drivers. Two contrasting phytoplankton annual cycles characteristic of these temperate waters were distinguished. PCA discriminated the inner and outer areas separated by a complex frontal system. The gulf's inner waters showed a bimodal phytoplankton cycle (maximums in autumn and spring) associated with the seasonal stratification of the water column in deeper areas and the consequent nitrate limitation in summer. The outer waters adjacent to the continental shelf showed unimodal cycles (maximum in autumn or spring) linked to the vertical mixing of the water column in shallow areas with moderate light intensity and nitrate availability. For both annual phytoplankton cycles, light is the main limiting factor in winter. Finally, the analyzed environmental patterns suggest that a tidal front favor feeding and spawning fishery re-sources in the north of the gulf.