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Aim:To verify the temporal dynamics of Limnoperna fortunei larval stages and to identify the main environmental variables driving the larval density patterns in an area highly impacted by reservoirs. Methods: Samplings were performed quarterly, from February to December 2014, in 10 transects along to the Paraná River main channel. For each sample site, 100 L of water were filtered. The filtrated was fixed in alcohol 80%, and the larval stages were counted and classified under the optical microscope. Concomitant to biological collections we took some of the main water variables. We performed a Redundancy Analysis (RDA) in order to summarize the variations in densities of larval stages in relation to the main physical and chemical water variables. Results: We found a total of 200,590 L. fortunei larvae, in which 83.6% were identified as the initial stages. The most abundant months in L. fortunei larvae were December and February. The first two axes of RDA sum up 96% of the total data variation, and the most significant environmental variables explaining variations in larval densities were: water temperature, total nitrogen, electrical conductivity, phosphate, dissolved oxygen, depth and ammoniac ion. The warmer months were influenced by the major values of water temperature and depth, besides the higher densities of all larval stages. Conclusions: Our results indicate that L. fortunei reproduction follows a general pattern throughout the upper Paraná River floodplain, what seems to occur mainly between February and December. Thus, we suggest that measures for the L. fortunei control should be done during low-density periods (i.e., April to August), when the water level is low, and consequently, the dispersion of this species might be limited.Keywords: area of environmental preservation; propagule pressure; golden mussel; reproduction.Resumo: Objetivo: Verificar a dinâmica temporal dos estágios larvais de Limnoperna fortunei, e identificar as variáveis ambientais direcionadoras desses padrões, em uma área altamente impactada pela construção de reservatórios. Métodos: As amostragens foram realizadas trimestralmente, de 2

Limnoperna fortunei Dunker, 1857 is an Asian invasive freshwater bivalve. Although there need to contain their spread, studies about the biology of the larvae are scarce. We correlated the larval stages of L. fortunei with biotic factors such as phytoplankton and main abiotic variables in lotic environments of the Upper Paraná River floodplain. The four samples were taken quarterly during the year 2012. The Principal component analysis (PCA) showed only spatial differences, as did a Canonical Correspondence Analysis (CCA). High densities of larvae were recorded in all samples the Paraná River and Baía River only in December, especially those in their initial stage. In the biovolume of Class of algae, Bacillarophyceae showed the highest value, but Chlorophycea who was strongly correlated with the density of D-stage larvae. The large variety of phytoplankton, especially microplankton Chlorophyceae, high values of PO 4 , NH 4 and temperature were positively correlated with high densities of D-stage larvae. We conclude that high temperature, and food availability, indicated by phytoplankton community, favored the reproduction of L. fortunei and enhance the ability of specie dispersion due to the increase in the emission of propagules. Therefore, studies that address the biology of golden mussel larvae should be performed in order to prevent its spread.Keywords: invasive species, limnic bivalves, Paraná river, dispersal patterns, environmental filters. Palavras-chave: espécie invasora, bivalves límnicos, rio Paraná, padrão de dispersão, filtros ambientais. Larvas de Limnoperna fortunei

Limnoperna fortunei is an invasive mussel species that is continuously expanding through South American. It has five larval stages, which usually differ in tolerance to environmental factors. How different abiotic filters affect L. fortunei larval stages has not been studied in depth. We employed a detailed database describing five floodplain environments to investigate the distribution of L. fortunei larval stages within and among these environments and determine which local abiotic filters affect the density of each larval stage. We found that the two youngest larval stages accounted for up to 83% of the larval density in four of the five environments studied, confirming an expanding population pyramid of L. fortunei in these environments. We also found positive and negative relationships among abiotic filters, and these relationships affected, directly and indirectly, the density of the youngest larval stages. Turbidity, water level, and suspended inorganic matter directly decreased the density of the two youngest larval stages. Conversely, temperature and pH directly increased the density of D-shaped and umbonated stages, respectively. Additionally, water level indirectly increased the density of the youngest larval stages mediated by declines in turbidity and suspended inorganic matter. Our findings suggest a likely expansion of L. fortunei in the Upper Paraná Floodplain. However, local abiotic filters, such as turbidity, water level, and suspended inorganic matter, decrease the density of the youngest larval stages. This finding illustrates that the establishment of L. fortunei can be prevented mainly if the youngest larval stages are controlled.