ROLE OF NUTRIENTS IN THE PHYTOPLANKTON DEVELOPMENT DURING A WINTER DIATOM BLOOM IN AN EUTROPHIC SOUTH AMERICAN ESTUARY (BAHÍA BLANCA, ARGENTINA)

CARLA V. SPETTER; CECILIA A. POPOVICH; ANDRES H. ARIAS; RAUL O. ASTEASUAIN; RUBEN HUGO FREIJE; JORGE E. MARCOVECCHIO

JOURNAL OF COASTAL RESEARCH

COASTAL EDUCATION & RESEARCH FOUNDATION

Lugar: Florida; Año: 2015 vol. 31 p. 76 - 87

0749-0208

The Bahia Blanca Estuary is considered as highly eutrophic. Here, long-term studies have shown that the winter-early spring bloom can be considered as the development of a diatom assemblage with Thalassiosira curviseriata as the dominant species. Since 2003 several changes have been observed in the annual pattern of nutrients and phytoplankton. In order to assess the availability of nutrients and their relationship with phytoplankton development, nutrient variability was studied during a winter bloom in 2003 (April 22nd to September 4th). Nitrite, nitrate, ammonium, phosphate, silicates, chlorophyll a, phytoplankton abundance, particulate organic matter and physicochemical parameters were measured in surface water at Cuatreros Port. In the Sauce Chico River mouth was determined the concentration of nutrients to estimate the input of this river. The results of this study were compared with a previous usual diatom bloom (2002). In 2003, the bloom was dominated by Cyclotella sp. with high chlorophyll a concentrations (26.5 - 40.4 microg L-1). T. curviseriata was presented only at three sampling dates reaching up to 19% of the total abundance. Mean values of dissolved oxygen, nitrate, oxygen saturation percentage and salinity were significantly higher in 2003 than 2002; while, N:P ratios were significantly lower. Si was never limiting. A shift in the limiting nutrient between the two years (N in 2003 and P in 2002) could have lead to a change in species dominance during the blooms. Results suggest that the nutrients levels in the coastal ecosystems as Cuatreros Port play an important role in the control of phytoplankton dynamics during the productive period and partially explain its inter-annual variability.