Densidade e estrutura populacional das larvas de Limnoperna fortunei Dunker 1857, e os efeitos da resiliência do rio Paraná sobre sua população.

Abstract

The drainage basin of the Upper Paraná River has suffered several anthropic impacts, among which, the construction of reservoirs, which cause various changes in the chemical and physical features of the habitat. This basin presents a free 230 km stretch of these developments, which holds high biodiversity, but also allocates several invasive species, among them, the Limnoperna fortunei. This bivalve is native to the Asian continent, and has been present in South America since the early 90?s. These individuals present a plankton habit during the larval phase and, a fouling habit during their adult phase, which facilitates their dispersion by the movement of water and the traffic of vessels. This specie, as well as other invasive species, represents a great threat to biodiversity of the Upper Paraná River basin. To understand the temporal population dynamics of larvae of L. fortunei and to verify the role of the Porto Primavera reservoir on larval densities of this species, we performed collections along the free 230 km of dam of the upper Paraná River. In this study, we identified the factors driving the temporal dynamics of L. fortunei to describe variations in its larval stages density. We verified the effects of the Porto Primavera reservoir and the resilience of the Paraná River after its construction on the density and structure of the L. fortunei larvae population. We measured the contribution of the main tributaries that flow in this stretch of Paraná River for the variations in limnological variables in relation to a distance gradient of the Porto Primavera reservoir. We found that temperature is the main driver of the reproduction of this species, since in the warmer months the highest densities of the initial larval instars were recorded. This period coincides with the period of high waters of the Paraná River, which increases the emission of propagules of L. fortunei and can facilitate their establishment in new environments. We also observed that in the most distant portion of the Porto Primavera reservoir the limnological conditions approximate the natural values (previous to the construction of this reservoir), and that the tributaries contribute to the restoration of these variables, especially for Secchi and phosphorus total. In these regions farther from the Porto Primavera reservoir, larval densities are lower, which demonstrates that river resilience may be a possible environmental filter for the L. fortunei invasion.