Melisa D. Fernández Severini

Planktonic food and foraging of Eubalaena australis, on Peninsula Valdés (Argentina) nursery ground

Se reportan observaciones sobre alimentacion de la ballena franca austral y zooplancton disponible, realizadas en Bahia Piramides (Golfo Nuevo). Se compararon datos de plancton, comportamiento trofico de las ballenas y temperaturasalinidad y clorofila-a registrados los dias 10 y 19 de octubre de 2005. El 19/10 la biomasa zooplanctonica fue significativamente mayor, observandose un numero alto de ballenas filtrando en superficie. Esta conducta se observo desde el 17 al 21/10. El evento de forrajeo descrito, confirma que la ballena franca se alimenta en este zona reproductiva de parches de zooplancton con una adecuada composicion y alta densidad, en primavera.

Tidal time-scale variation of inorganic nutrients and organic matter in Bahía Blanca mesotidal estuary, Argentina

Land-derived materials are regulated by coastal and shelf environmental conditions before being transported to the open sea. It is of great concern to understand the processes and to establish the extent in which they modify terrestrial compound fluxes, such as nutrients, that end up in the oceans. At present, one of the topics that arouses the highest interest within environmental coastal studies is the direction and magnitude of inorganic nutrients and the exchange fluxes of organic matter between the water column and the associated tidal plains during the daily tidal cycle. These processes, together with the local hydrographic conditions, define the key role of this type of environment: its function as a nutrient and organic matter reservoir and/or as a source. A research programme directed to understand this mechanism within mesotidal estuaries was developed in the Bahía Blanca estuary, on the coast of Buenos Aires (Argentina). On a tidal time-scale basis, levels of DIN (nitrate + nitrite + ammonium), DIP, DISi, and organic matter were measured in the estuarine water column and tidal plain porewater, for two years. Results showed no significant variations during the tidal cycle, even though the temporal variation of these compounds was clearly identified. In addition, the biological production of the estuary was considered and taken into account, so as to understand the organic matter cycle within the system. Particular conditions of the environment (sediment characteristics, porewater chemical environment, hydrodynamics, anthropogenic sources, etc.) were also considered to help fully understand the results.

Mesozooplankton composition and spatial distribution, Nuevo Gulf, Patagonia, Argentina

The composition and spatial distribution of mesozooplankton of Nuevo Gulf, Argentina, were analyzed from surface samples taken on July, 1997. A total of 32 taxa were recorded. The highest abundances were found close to Nueva Bay, which is located nearby a growing urban population, whereas the lowest values were detected in the center of the gulf. Holoplankton dominated at all stations and evidenced a homogeneous spatial distribution. Meroplankton showed a more heterogeneous pattern. Ctenocalanus vanus was the most abundant taxon followed by Paracalanus parvus . Gastropoda veligers dominated the meroplanktonic fraction. Our results showed that the spatial distribution of the mesozooplankton seemed to be mainly influenced by the dominant hydrological circulation pattern of the region. This research establishes the first scientific basis for further studies in zooplankton communities of this important gulf, closely related to a natural protected worldwide known area declared a world heritage site by UNESCO.

Distribution and behavior of zinc in estuarine environments: an overview on Bahía Blanca estuary (Argentina)

Zinc concentrations and distribution have been fully studied within Bahía Blanca estuary, an area which is strongly influenced by urban and industrial stress. Not only metal dissolved in estuarine water were measured but also measured were sediments and suspended particulate matter (SPM), as well as associated with estuarine organisms. In all cases, internationally standardized protocols were applied to metal measurements, including analytical quality check test through analysis of certified reference materials. Total metal contents from surface sediments and SPM were compared with those from a historical database of the area, as well as with values representing the natural geochemical baseline within the system. Results showed that heavy metal pollution is mainly localized in the areas close to both industrial effluents discharge system and urban sewage outfall discharge. Data from sequential extractions indicate that metals from anthropogenic sources are potentially more mobile than those inherited from geological parent material. The influences of other potential sources of metals (i.e., streams, runoff) were also considered. SPM was clearly identified as the main carrier of the studied heavy metals within the system, and its significance to metals input into sediments and/or biota was verified. Zinc has been accumulated within the different biological species from Bahía Blanca estuary, and their kinetics of accumulation have also been considered. Finally, the combination of the obtained results allowed suggesting the maintenance of a surveillance program to assess the environmental quality of this environment.