The population dynamics of the "cholga" Cardita affinis (Sowerby 1833) from Málaga Bay, Colombia, was studied from December 1999 to February 2002, which included the 1999-2000 La Niña event (LN) and the post-LN period 2001-2002. This climatic deviation caused precipitation anomalies in Málaga Bay. Salinity, precipitation, and sea surface temperature anomalies were highly correlated with the bivalve's body mass cycle. Irregular spawning events were observed during LN by comparison with the regular period. Individual growth and mortality were found significantly higher during LN than during the post-LN period while longevity was almost twofold lower during LN. Increased mortality was probably related to environmental stress. Individual production and productivity were higher during LN, although the annual biomass was lower than during the post-LN period. These results may be related to higher food availability during LN, which agrees well with the results on growth performance. The observed changes provide a base line for future studies regarding effects of El Niño/LN events on population dynamics of tropical bivalves. © Springer-Verlag and AWI 2007.