Plankton Ecology and Biodiversity in the Bahía Blanca Estuary

Abstract

The Bahía Blanca Estuary encompasses an extensive flat area covered by islands, saltmarshes, mudflats and tidal channels. This spatial heterogeneity confers to theecosystem the capacity to hold large biodiversity; in particular, the estuary is an importanthabitat for numerous permanent and migratory species of commercial and ecologicalimportance, including fishes, birds, invertebrates and mammals. Due to its interconnection with land, large gradients of salinity, nutrients, organic carbon and turbidity characterize the inner part of the estuary where plankton has developed ecophysiological adaptations to sustain natural populations. In addition, urban and industrial settlements within this area pose additional threats to plankton communities. In recent years, however, specific plankton groups have revealed profound changes, denoting that the present rate of environmental change is exceeding the adaptive capacity of organisms. This chapter provides a comprehensive long-term examination of the main planktonic groups (phytoplankton, microzooplankton, mesozooplankton and jellyfish), their speciesdiversity and temporal and spatial dynamics. This section further examines the ecologicaladaptations of plankton to survive under wide environmental gradients and identifiesmain biological shifts, including the introduction of invasive species, species replacement, low reproductive capacity, phenological changes and the biomass decline of specific plankton groups in the last 40 years. Experimental and long-term field observations allowed the attribution of such changes to multiple interactive effects of environmental drivers, highlighting rising water turbidity and temperature, eutrophication, pollution and expansion of exotic species as the main sustain drivers. The assessment of environmental variability and trend feedback provides the baseline toidentify key plankton vulnerabilities and to delineate effective mitigation plans within theBahía Blanca Estuary.