Limnetica 33

Sinelobus stanfordi (Richardson, 1901) is a euryhaline tanaidacean distributed worldwide and recorded in the freshwater zone of the Río de la Plata estuary. Despite the vast bibliography on this species, its sensitivity to pollution has never been assessed. This study was conducted in the coastal freshwater tidal zone of the Río de la Plata estuary, encompassing approximately 170 km of Argentine shoreline subjected to different types of anthropogenic disturbance. Benthic samples were taken seasonally in triplicate in vegetated zones, along with 19 sampling sites from 2005 to 2010. To explore the main environmental gradients within the study area, a principal component analysis (PCA) was conducted. For the interpretation of the most relevant variables, the axis defined by PCA was followed by a varimax-normalised rotation. The ecological optima and tolerance limits of S. stanfordi were calculated for each environmental variable analysed. The multivariate analysis suggested that most of the variations within the study area could be related to the impact of anthropogenic pollution as well as the natural dynamics of the estuary. The abundance of the species was significantly lower in sites with high levels of nutrients and oxygen demands, exhibiting a negative correlation with soluble reactive phosphorous concentrations and a positive correlation with oxygen levels. Turbidity and conductivity did not represent limiting variables for the distribution of this tanaid.

This study constitutes the first approach to assess the effect of anthropogenic disturbance on the populations of this crustacean and contributes to the knowledge of tanaidacean ecology. The low species abundance in the most polluted sites would suggest that S. stanfordi could be useful in biomonitoring studies in the Rio de la Plata estuary as well as other temperate estuarine systems.