Field and laboratory observations of the mass mortality of the yellow clam Mesodesma mactroides in South America: the case of Isla del Jabalí, Argentina.

FIORI, S. M.; VIDAL-MARTÍNEZ V.; SIMÁ-ÁLVAREZ R.; RODRÍGUEZ-CANUL R.; AGUIRRE-MACEDO M. L.; DEFEO, O

JOURNAL OF SHELLFISH RESEARCH

National Shellfisheries Association, Inc.

Lugar: Connecticut, U.S.A.; Año: 2004 vol. 23 p. 451 - 455

0730-8000

Mesodesma mactroides (Deshayes, 1854) has experienced mass mortalities throughout its biogeographic range (23°S to 41°S) along Atlantic exposed sandy beaches of South America. However, there is no information about the potential causes underlying these large-scale events. In the summer of 2002 sudden massive mortality almost decimated the yellow clam population located to the south of Isla del Jabalí (Argentina), at the southern edge of its geographical range. Field observations showed a drastic decrease in abundance from 2000 to 2002, without recovering since then. Mortality sequentially occurred in the beach in a north-south direction, following the same trend as in the large-scale event. Significant differences in individual size were found between dead and live clams with the largest individuals of the population being the most affected. Histological analysis revealed the presence of a meront stage of an unidentified coccidian parasite in the epithelium of the middle intestine of 3 of the 14 clams examined. Necrosis was found in gills and stomach in 13 of the 14 clams examined. The results suggest that these parasites could play a role in the massive mortality events of the yellow clam populations all along South American sandy beaches since 1993. These findings provide an alternative explanation to the widely held notion that mass mortalities in sandy beach macrofauna are due to harmful algae blooms.