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: Several species of ecosystem engineers inhabiting coastal environments have been reported structuring different kinds of communities. The magnitude of this influence often depends on the habitat complexity introduced by the engineers. It is commonly accepted that an increase in habitat complexity will result in an increase in diversity and/or abundance in the associated fauna. The rocky salt marshes along the coast of Patagonia are dominated by cordgrasses, mussels, and barnacles forming a mosaic of engineered habitats with different complexity. This system allows us to address the following questions: how different is a macroinvertebrate assemblage when dominated by different ecosystem engineers? And, is there a positive relationship between increasing habitat complexity and the species richness, diversity and total density of the assemblages? To address these questions, we compared the three ecological scenarios with decreasing habitat complexity: cordgrass-mussel, mussel, and barnacle-engineered habitats. We found a total of 22 taxa mostly crustaceans and polychaetes common to all scenarios. The three engineered habitats showed different macroinvertebrate assemblages, mainly due to differences in individual abundances of some taxa. The cryptogenic amphipod Orchestia gammarella was found strictly associated with the cordgrass-mussel habitat. Species richness and diversity were positively related with habitat complexity while total density showed the opposite trend. Our study suggests that species vary their relative distribution and abundances in response to different habitat complexity. Nevertheless, the direction (i. e., neutral, positive or negative) and intensity of the community's response seem to depend on the physiological requirements of the different species and their efficiency to readjust their local spatial distribution in the short term. © 2010 Springer-Verlag and AWI.