Massive mortality of the Asian clam Corbicula fluminea in a highly invaded area

Abstract

Corbicula fluminea is one of the most widespread invasive species in aquatic ecosystems. Originating from Southeast Asia this clam has been dispersing worldwide over the last decades (Darrigran 2002; McMahon 2002; Sousa et al. 2008b). Corbicula fluminea was first reported in the Minho estuary in 1989 (Araujo et al. 1993), and is now a major component of the benthic fauna in terms of density and biomass, contributing to more than 95% of the overall biomass (Sousa et al. 2008e). Recently, the C. fluminea population has been undergoing rapid die-offs in the Minho estuary, due to extreme abiotic changes that have been occurring in the summer (e.g. low river flow, high temperature, low dissolved oxygen and lower redox potential). The first documented event occurred in the summer 2005, and was associated with a strong heatwave. The major declines in C. fluminea density and biomass occurred in estuarine areas with fine sediments and rich in organic matter content (Sousa et al. 2008a, d). Environmental impacts resulted from the 2005 heatwave and the synergistic effects caused by the great mortalities of C. fluminea were responsible for dramatic changes in the macrozoobenthic estuarine community (Sousa et al. 2008c), with the native bivalve populations (e.g. Pisidium amnicum, Unio pictorum, Anodonta anatina and Psilunio littoralis) being severely affected. However, C. fluminea rapidly recovered from this impact, returning in the subsequent years to the earlier density and biomass (Sousa et al. 2008c). In September 2009, local fisherman reported massive accumulations of soft putrefying parts of this Asian clam at the water surface, suggesting another massive die-off. Given the ecological importance of this phenomenon, and since a long data set concerning the ecology of C. fluminea in this estuary already exists (Sousa et al. 2008a, d), the aims of the present study were to report the first results of the recent massive mortality of C. fluminea in the Minho estuary, and also to discuss the ecological changes resulting from this occurrence.

Martina Ilarri

Postdoctoral researcher

My research interests include the ecological impacts of biological invasions in a changing climate.