Caracterização da comunidade zooplanctônica e sua relação com as variáveis ambientais no Furo da Laura (Vigia-PA).

Abstract

Studies involving zooplanktonic communities and their relationship with tropical ecosystems is a difficult task due to the great diversity of natural or anthropogenic factors that influence environmental processes. However, the present work aims to perform the environmental characterization of the studied estuary, through the analysis of the physico-chemical variables of water, as well as characterize the distribution of zooplanktonic organisms in this environment, from its identification and quantification. Samples were collected every two months for a hydrologic cycle, the four sampling stations in its tidal variations (ebb and flow) as well as collections Diel two seasonal periods, for which was used only a fixed point. The samples were collected by horizontal trawls on the surface of the water column using a plankton net (200μm mesh) and then preserved in 4% formalin, neutralized with sodium tetraborate. Physical-chemical parameters (temperature, pH, salinity, dissolved oxygen and electrical conductivity) were measured in situ, with a multiparametric probe simultaneously to the biological collections. In the laboratory, the identification of qualitative samples was performed at the lowest possible taxonomic level. From the quantitative analyzes, the density (org.m3) of the different groups identified was determined and the relative abundance and the frequency of their occurrence were calculated. Diversity, equitability and dominance in the distribution of organisms were estimated by the Shannon-Wiener (H '), Pielou (J') and Berger-Parker indices, respectively. Tests of normality and significance were performed between the data available in the two campaigns. The Principal Component Analysis (PCA) and Hierarchical Grouping Analysis (HCA) were performed to evaluate the relationship between available data. The environmental variables showed no significant variations during the study period. The species considered very common throughout the study were the larvae of Polychaeta, Gastropoda, Bivalve and barnacle, the nauplii of copepods, Acartia tonsa, Parvocalanus crassirostris, Paracalanus nanus, Paracalanus sp, Pseudodiaptomus sp1, Oithona nana, Cyclops sp, Cyclopoida, Calanoida, Harparcticoida, Poecilostomatoida. The copepods were the most abundant in the study space-time, with domain trend, while in the diurnal study was highlighting the group of cirripedia in the dry period and Calanoida in the rainy season. The highest densities of the bimonthly study were in July / 12, whose richness was the lowest recorded and in the case of the study of circadian variation, the highest zooplankton density was verified in the dry period. In the bimonthly and nictemeral studies the specific diversity presented a similar pattern. There was no statistically significant difference between the densities of the dry period and the rainy season, as well as between the data of temporality, spatiality and tidal regime. The Cluster Analysis applied to the zooplankton groups of the bimonthly study allowed to identify three clusters formed according to the similarity between their distributions. In the analysis of the nictemeral study, applied to the collection schedules, it was observed the separation of the samples by seasonal periods (dry and rainy). In the PCA analyzes, it was possible to observe the influence of the environmental variables in the bi-monthly campaigns and the seasonality in the nictemeral campaigns.