Fast response of freshwater consumers to a new trophic resource: Predation on the recently introduced Asian bivalve Limnoperna fortunei in the lower Paraná river, South America

SYLVESTER, FRANCISCO; BOLTOVSKOY, DEMETRIO; CATALDO, DANIEL

AUSTRAL ECOLOGY

Blackwell

Lugar: Oxford; Año: 2007 vol. 32 p. 403 - 415

1442-9985

Comparison of Limnoperna fortunei numbers and biomass in screened (5, 15 and 40 mm) and unscreened cages deployed for 18 months in the lower Paraná delta indicates that predators harvest 26–79% (numbers), or 20–85% (biomass) of the mussel population. Predation impact decreases with mussel size. On average, 6 kg of whole live mussel ´ m–2 ´ year–1 (0.36 g of dry mussel tissue ´ m–2 ´ day–1) were eliminated from the unscreened cages. Cages with 15 and 40 mm screens lost between 1 and 2 kg ´ m–2 ´ year–1. Aquatic mammals, birds, and especially fish, are probably the main consumers of large mussels. Small L. fortunei are most probably eaten by fish and also by several invertebrates, including crustaceans, leeches and gastropods. It is suggested that L. fortunei intercepts a significant fraction of the organic carbon that the Paraná-Uruguay rivers flush into the ocean, locally boosting numbers of benthophagous animals, deposit feeders and, indirectly, higher level predators. Our results indicate that only 15 years after its first introduction in South America this invasive species is very actively consumed by local predators, but predatory suppression of the mussel seems very unlikely. Comparisons with the effects reported for the zebra mussel (Dreissena polymorpha) in Europe and North America suggest that L. fortunei is consumed more actively and that its negative impact on the local fauna is more restricted. These differences are attributed to the fact that while D. polymorpha feeds chiefly on plankton, a limited resource, L. fortunei feeds on detrital particulate organic matter, whose supply in these large South American rivers largely exceeds consumption.