Ictioplâncton em um estuário tropical sob influência da hipersalinização

Abstract

Tropical estuaries are important feeding and nursery habitats for many fish species. These processes are influenced by the biotic and abiotic conditions presented by estuaries. The knowledge of the abundance and seasonal distribution of ichthyoplankton in hypersaline estuaries is of great importance for estuarine ecology, since these environments present communities with peculiar characteristics. The present study was conducted in an inverse type estuary, with marked hypersaline conditions, due to a period of intense drought in the region (2012-2015). Despite its importance, knowledge about ichthyoplankton in hypersaline tropical estuaries is scarce. The present study evaluated the most appropriate methodology (mesh types of nets) as well as the seasonal distribution of fish eggs and larvae in a hypersaline estuary (Piranji, northeast Brazilian coast). The samples of ichthyoplankton were collected bimonthly during the year 2015 through conical-cylindrical plankton networks, with mesh opening of 200, 300 and 500 µm. The results showed that the dry period had an average salinity of 49.24 ± 8.75, while in the rainy season the mean was 36.46 ± 14.56. The 500 µm net showed the highest egg collection efficiency (56%), while the 200 µm net collected the highest relative abundance of larvae (56%). Six egg taxa and seven species of larvae were identified, belonging to seven families of larvae (Engraulidae, Gobiidae, Gerreidae, Carangidae, Scienids, Echeneidae and Syngnathidae). The most abundant species was the manjuba Anchovia hepsetus. The PERMANOVA analysis showed that there was no seasonal variation in the ichthioplankton assembly, indicating a homogenization and simplification of the communities. The BEST test revealed that salinity and copepods were the variables that best explained the larval distribution pattern. The study suggests that the inclusion of the 200 µm mesh may provide a more complete sampling of estuarine ichthyoplankton. The results combined with a literature review suggest that high levels of salinity (hypersaline condition) may be an important factor in determining the composition of estuarine ichthyoplankton and affect the nursery function of mangroves