Long-term variability in summer phytoplankton blooms as fingerprints of climate change in a temperate estuary in the southern hemisphere

GUINDER V. A.; POPOVICH C. A.; MOLINERO J. C.; PERILLO G. M. E.

Boulogne sur Mer, Francia

Workshop; Climate Change Impacts on Estuarine and Coastal Ecosystems: a Zooplankton Perspective; 2010

Universidad de Lille, Francia

Spring phytoplankton blooms are ubiquitous in temperate coastal systems, while summer blooms have gained attention in the last decade as a consequence of recurrent strong phytoplankton blooms. Although these changes have been linked to both climate-related environmental changes and increasing anthropogenic disturbances, the causes remain matter of debate. Here we have examined long-term phytoplankton data covering the austral summer period, (December – March, 1978 to 2008) and compared with hydrological and meteorological variations in the Bahía Blanca region. Chlorophyll concentration remained constant over the studied period while the phytoplankton abundance (in cells l-1) increased exponentially. The phytoplankton community composition showed a shift from the dominance of phytoflagellates and relatively large diatom species towards a dominance of a small (5-15 µm) diatom species: Thalassiosira minima (up to 86 % of the total abundance in summer 2008). Long-term atmospheric conditions revealed a trend towards a warmer and drier environment which affected the hydrographic elements in the estuary (i.e. warmer and saltier waters). These shifts in water mass properties have likely affected phytoplankton species niches in recent summers eventually promoting T. minima outburst and dominance over other species.These results allow hypothesizing that the climate warming is triggering the occurrence of summer phytoplankton blooms and modifications in community structure in the Bahía Blanca Estuary. Further studies should focus on the autoecology of T. minima to evaluate species’ life history responses to both climate and anthropogenic disturbances.