Intermittently Closed Estuaries and Tadpole Communities: Influence of Artificial Breaching

Abstract

Naturally or mechanically opening the sand bar of intermittently closed estuaries (ICEs) plays an important role in the proper functioning of these systems. In this study, the impacts of artificial breaching of a coastal lagoon on anuran communities (composition, richness, and abundance) were investigated in the Lagoa do Peixe National Park floodplains, southern Brazil, from 2007 to 2009. The sampling period included two lagoon openings and occurred four times when the lagoon was open and four when it was closed. Artificial opening of the lagoon considerably changed the salinity and availability of temporary ponds in the estuary floodplains. Tadpole species richness and abundance were higher in areas influenced by the sand bar opening than in floodplain areas not influenced by this management. Although salinities were higher when the lagoon was open, only species that do not reproduce explosively occurred in significantly lower abundance. Multivariate analyses demonstrated that anuran species composition differed between areas affected and not affected by the lagoon opening. The composition gradient was associated with conductivity, hydroperiod, and floodplain management. These differences likely relate to individual traits of each species (e.g., habitat preference and reproductive mode). The study suggests that amphibian communities in the Peixe lagoon floodplains are resistant to oligohaline conditions when the lagoon is open. However, projected sea level rise and planned increasing drainage of freshwater wetlands could raise the salinity levels in floodplains to polyhaline or even euhaline conditions. Thus, artificially opening the sand bar for fishery management should be done with caution.