Environmental variables driving the larval distribution of Limnoperna fortunei in the upper Paraná River floodplain, Brazil

Abstract 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.