Descripción: The coast of Lobería and Necochea is characterized by cliffsand narrow beaches. The inlet of the Quequén Grande river used to alter the coastline. The construction of jetties related to the Quequén Harbour induced huge accumulations of sand towards Necochea, and a critic erosive process of cliff and beach to the east. Beach width reduces from 300 m at the west to 40-60 m to the east. Considering regional sand scarcity, the eastern beaches are characterized by more sand variability. Greater variations in the sand balance were assigned to human activity. Waves coming from the E, SE and S deliver more energy along this eastern sector. On the other hand, submerged zones of these beaches have less availability of sand. Greater availability of fine sand was recognized towards Necochea. The Quequén Grande river has much effect on the estuarine dynamics during ENSO-triggered floods, although sedimentation is dominated by silt supply.

Descripción: Fil:Simionato, C.G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: For the first time a taxonomic and ecological study of species belonging to Helicostomella was performed over a mesoscale spatial distribution by examining ca. 3000 loricae collected in Argentine shelf waters during the austral autumn. Microscopic and statistical analysis revealed that the general shape and the oral diameter remained practically constant in the whole area surveyed, despite a continuous length fluctuation of ca. 300 μm, which includes the entire range present in eight previously reported species. Consequently, we consider that the genus may be represented only by H. subulata, whose strong fluctuations in length (mostly attributed to an increase in the collar length), density and biomass seem to respond to temperature, food availability and front-related processes. In Buenos Aires coastal waters associated with a quasi permanent estuarine front (40-40.5°S), mixed conditions would favour moderate abundances of long loricae, whereas in northern (42.5-45.5°S) and southern (46-54.5°S) Patagonian waters, high (103 ind. L-1) and low (<5 ind. L-1) densities of short loricae seem to be a consequence of stratification and encystment, respectively. The non-occurrence of the species at 41-42°S, together with a three-fold reduction in length-related parameters between specimens from Buenos Aires and Patagonian waters, suggests a disjunct distribution.