The potential of Glycymeris longior (Mollusca, Bivalvia) as a multi-decadal sclerochronological archive for the Argentine Sea (Southern Hemisphere).

In the absence of instrumental records, shell growth increments of bivalves are used to build continuous multi-decadal time series of growth and to estimate environmental variability. While there is interest in such chronologies in the Northern Hemisphere, there is a lack of multi-decadal datasets of growth for marine species from the Southern Hemisphere. We assessed the potential of the clam Glycymeris longior as an environmental proxy archive for the mid-latitudes of the South Atlantic Ocean, by applying sclerochronological techniques on the shells of individuals from a coastal area in Northern Patagonia, Argentina. Growth of G. longior showed a synchronous pattern, and shells were cross dated. We demonstrated that G. longior shells can be used to generate a robust multi-decadal chronology. The chronology spanned for a period of 22 years, from 1990 to 2011. This chronology has the potential to be extended, given that the maximum longevity of the analysed shells was 69 years. Significant positive correlations were found between the chronology and sea surface temperature and the Southern Annular Mode index. The sclerochronological approach performed in this study is a first step toward a long-term understanding of the links between climate and growth patterns of bivalves in temperate regions of SW Atlantic Ocean, under a long-term perspective.

Bonamiosis status in natural Ostrea puelchana beds in San Matías Gulf (Patagonia, Argentina), 14 years after an epizootic.

Between 1995 and 1996, Bonamia exitiosa caused an epizootic in San Matías Gulf, Argentina, that spread from a commercial culture site of Ostrea puelchana to natural beds located at the northeastern coast of the gulf. A mortality rate of 95% was registered in cultured oysters, and oysters from natural beds were also affected. The aims of this study were to assess the parasite prevalence in oyster beds and the demographic structure 14 yr after the epizootic. Two different oyster beds were studied during 2009 and 2010. Parasite prevalence was studied related to oyster aggregation, density, sex, and oyster size. Prevalence reached 35.3% at Las Grutas and 18.9% at Banco Reparo and was proportionally associated with density. Prevalence was also associated with the type of aggregation in Banco Reparo, where carrier oysters were more infected. Infection was independent of sex category, and infected oysters were larger than the non-infected ones. Oyster density decreased markedly compared to previous studies in both beds and mean sizes were lower, while prevalence doubled. Because of the persistence of the beds in this period, disease seems to control the population structure.