Environmental modulation of reproductive activity of the invasive mussel Limnoperna fortunei: implications for antifouling strategies

Limnoperna fortunei (Dunker, 1857) (Bivalvia) invaded Argentina through the Rio de la Plata estuary around 1990 and is presently established throughout five South American countries as a dominant component of the benthic fauna and a major nuisance for industry and power plants. Between 1997 and 2006 we monitored the reproductive activity of L. fortunei through weekly measurements of planktonic larvae in six South American water bodies: Rio de la Plata estuary, Parana and Carapachay rivers, Salto Grande, ItaipU and Embalse de Rio Tercero reservoirs. Mean larval densities varied between 4000 and 7000 individuals m-3; except in the reservoirs of ItaipU (450 ind. m-3) and Salto Grande (869 ind. m-3), where the mussel was first recorded shortly before our surveys, and upstream dispersal is limited (Salto Grande). In all cases, reproductive output decreases during the winter. At four of the six sites surveyed larval densities were comparatively high for 8.8-10.2 months per year. A lower food supply is possibly responsible for the shorter reproductive period of 5.9 months at Embalse. At Salto Grande, there is a well-defined mid-summer drop in larval numbers, coinciding with blooms of cyanobacteria. We propose that, in addition to temperature, two major factors may regulate the reproductive activity of L. fortunei: (i) the availability of food; and (ii) blooms of toxic cyanobacteria, significantly shortening the otherwise very long reproductive period. This information is important for the design of antifouling programmes involving the use of molluscicides, and has potential for reduced biocide use. These results provide supporting evidence for some fundamental ecological theories of invasions discussed here.