Colonization and spread of Limnoperna fortunei in South America

Abstract

The invasion of the exotic bivalve Limnoperna fortunei (Dunker 1857) in South America started with its introduction, presumably with ballast water from transoceanic ships trading with southeast Asia, in the Río de la Plata estuary (Argentina) around 1990. From there it spread swiftly to cover most of the Río de la Plata basin. L. fortunei is now present in five South American countries: Argentina, Bolivia, Brazil, Paraguay and Uruguay, as well as the basins of Guaíba and Tramandaí (Brazil), Patos-Mirim (Brazil and Uruguay), and Mar Chiquita (central Argentina). These smaller watersheds were most probably colonized as a result of secondary human-mediated introductions from waterbodies of the Río de la Plata basin. Expansion was much faster along navigable waterways, especially the Paraná and its tributaries (around 250 km/year), and slower elsewhere (Paraguay and Uruguay rivers and their tributaries). Over 20 years after its introduction to South America, new waterbodies are still being colonized by L. fortunei (e.g., the first records of the mussel in the Tramandaí River, and in Peixoto, Quadros and Itapeva lakes date from 2013). Mussels have not been recorded in a few rivers of the Río de la Plata basin where their survival seems to be limited by excessively high suspended solid loads or salinities, or by the fact that they periodically dry out (e.g., rivers Bermejo, Pilcomayo, Salado del Norte, in north-central Argentina). South American populations display a relatively high genetic differentiation, confirming that geographic spread is strongly dependent on human activities: vessel and barge traffic is the main vector that helps to disperse the mussel locally through upstream "jumps" of adults attached to ship hulls. Genetic studies also suggest that there have been multiple introductions. By early 2014, L. fortunei had not yet been reported from any of the other major South American watersheds (Amazonas, São Francisco, Orinoco), but colonization of these basins is probably inevitable. Modeling of potential distribution based on habitat fitness indicates that extensive regions could support L. fortunei including much of lowland South America, southern Mexico, the southeastern United States, Europe, and tropical Africa.