Qual o efeito da hipersalinidade na distribuição de copépodes em um estuário tropical?

Abstract

Copepods are important indicators of ecological conditions because they are the link between producers and elevated levels of the estuarine trophic web. In the semi-arid region, intensification of drought periods may increase hypersalinity and influence salinity distribution in the estuaries, which may lead to seasonal and spatial changes in important components of the food chain. Despite the importance of the effects of hypersalinity, knowledge about its implications in zooplankton is scarce. The study analyzed the seasonal (dry and rainy), nictemeral (day and tidal) and spatial (along the estuary) distribution of copepods in a tropical estuary on the Brazilian semiarid coast. The hypersalinity condition was present in most of the study, even in periods of rain, reaching a maximum of 62 in an upstream area of the estuary in December 2015. The community, in general, presented low wealth, being dominated by few species resistant to hypersalinity conditions. Oithona oswaldocruzi, O. hebes, Parvocalus crassirrostris, P. scotti e Euterpina acutifrons were the most abundant ones. The results indicated that the nictemeral variation is controlled by salinity, tides and chlorophyll a. The community is similar between the dry and rainy season, which indicates a process of homogenization and simplification of biodiversity throughout the year, probably due to hypersalinity. The highest density was observed in the dry period, possibly due to the increase of the abundance of adapted species. The seasonal variation was controlled by salinity, total nitrogen, silica and chlorophyll a. The results also showed spatial variation along the estuary, with the lowest density being found furthest from the estuary mouth, in April, when hyposaline waters dominated. The largest density was observed closest to the mouth, in August, when the estuary was hypersaline. Considering the future scenario of rising temperatures, evaporation rates, rainfall reduction and more severe droughts, we conclude that the hypersalinity can generate a low wealth, with the consequent simplification of estuarine communities. Long-term studies are needed to test this hypothesis, as well as the elaboration of conservation strategies, especially in semi-arid estuaries.