Long-term decreasing trend of a blooming diatom (Thalassiosira curviseriata) in a temperate estuary of South America (Atlantic coast, Argentina)

POPOVICH C. A.; GUINDER V. A.; MARCOVECCHIO J. E.

IFM-GEOMAR, Kiel, Alemania

Conferencia; AQUASHIFT. Life in warming waters; 2010

IFM-GEOMAR

Bahía Blanca Estuary is a turbid and eutrophic coastal plain estuary located in a semiarid region on the Atlantic coast of South America. Phytoplankton and physico-chemical environment has been continuously studied since 1978 on a fortnightly basis. Up to 2002, the phytoplankton annual pattern in the upper zone was characterized as quasiregular and predictable with a recurrent winter-early spring diatom bloom dominated by Thalassiosira curviseriata. The massive growth of this key species in winter has been mainly attributed to low water temperatures, relatively low light intensities, maximum-nutrient stock and low grazing pressure.  In recent years (2003-2007), however, significant changes in the phytoplankton composition and species succession have been observed. The most noticeable change has been the significant decrease in the abundance of T. curviseriata, especially during June-August 2003, 2006 and 2007.  Long-term analysis of physico-chemical variables (e.g. dissolved nutrient concentrations, water temperature and turbidity) indicate that the decreasing trend of this species is mainly related to higher water temperatures in winter. Our results suggest that this diatom can be used as an accurate biological indicator of environmental modifications in the Bahía Blanca Estuary. Moreover, the shifts in the phenology of Thalassiosira curviseriata provide insights on the consequences of climate change in the southern hemisphere.