O efeito da hipersalinidade na biomassa de copépodes em um estuário semiárido tropical

Abstract

Estuaries are among the most diverse environments on the planet and can harbor in their waters a great diversity of organisms. Among these estuarine organisms, the copepods stand out. Copepods are microcrustaceans that dominate among zooplanktonic organisms. The objective of this work was to evaluate how the biomass of the most abundant copepods in the study area (Oithona spp. And Parvocalanus spp.) Reacts to the hypersalinity that occurs at the site. Rainfall (February, April and June) and drought (August, October and December) were collected in the Piranji River estuary (Northeast-Brazil). Samples were divided into P1, the farthest point from the sea, P2 the intermediate point and P3 closest to the sea. For the sampling were used conical cylindrical networks with mesh opening of 120 µm coupled with flowmeter. In the laboratory samples were processed and with the aid of stereomicroscope, 20 organisms from each of the two dominant taxa of the environment were identified for each month and each point sampled. After screening, images of the dorsal and lateral views of each organism were recorded using the LEICA LAS program. With these images it was possible to measure and obtain biovolume and thus obtain an estimate of biomass. Partial biomass, using only 20 individuals (partial), showed Parvocalanus spp. with higher biomass than Oithona spp. in all moments. This fact was not repeated when the total biomass in the environment was obtained, where Oithona spp. even presenting smaller dimensions, it presented superior biomass, which shows how high its density is in this environment. In quantitative terms, the maximum biomass values obtained were 27 ± 0.6 mg.Cm³ for Oithona spp. and 13 ± 0.8 mg.Cm³ for Parvocalanus spp. Regarding the averages, the highest were 11 ± 0.8 mg.Cm³ and 9 ± 0.7 mg.Cm³ respectively Parvocalanus spp. it was dominant only at the most downstream point of the estuary, with salinities more similar to coastal areas, an environment in which this organism has greater preference. Both taxa were adapted to the hypersaline condition of the region, showing no difference in total biomass between the regimes.