Nutrient - phytoplankton relationships during an atypical winter diatom bloom in Bahía Blanca estuary, Argentina.

CARLA V. SPETTER; CECILIA A. POPOVICH; RAÚL O. ASTEASUAIN; RUBÉN H. FREIJE; JORGE E. MARCOVECCHIO

Bahía Blanca, Argentina

Simposio; ECSA 44, Science and Management of Estauries and Coasts: A tale of two Hemispheres.; 2008

Estuarine and Coastal Science Association e Instituto Argentino de Oceanografía

Long-term studies in Bahía Blanca estuary have shown that the winter-early spring bloom can be considered as the development of a diatom assemblage (Thalassiosira spp. and Chaetoceros spp.) with T. curviseriata as the dominant species. So far, most studies try to associate the inception and duration of this bloom with the available pool of nutrients. The aim of this study focuses on the relationship between the dissolved macronutrients and the phytoplankton community structure during an atypical winter diatom bloom. From April 22nd to September 4th 2003, two Chl-a peaks (40.44 µg l-1 and 28.18 µg l-1) were observed in coincidence with the maximum values of phytoplankton total abundance (5.8 - 7.6 106 cells l-1). T. curviseriata was present only at three sampling dates reaching up to 19 % of the total abundance. In the opposite, a non-identified centric diatom (< 20 µm) was always dominant (90%). In pre-bloom period the DIN:DIP ratio was lower (8:1 to 14:1) respect to previous studies while DSi was abundant (114.7 ± 1.7 µM). During the bloom, a gradual decrease of all the analyzed macronutrients was observed. An important increase in DIN:DIP ratio occurred next to Chl-a peaks (59:1 and 83:1). Since the bloom collapse a DSi rise from 102.8 to 136.9 µM was registered. Results suggest that the observed changes in the dominant species of 2003 winter diatom bloom could likely not be due only to the different DIN:DIP ratios registered but also to another environmental factors.