Diversidade e abundância espaço-temporal da ictiofauna no litoral norte de Pernambuco

Abstract

Studies on the distribution and use of different coastal habitats by fish species are of great importance for the conservation and/or sustainable use of these environments and their resources. The fish community presents changes in its structural and ecological indices such as diversity and richness in different habitats. Thus, the present study aims to analyze the structure of the fish assemblage in a marine-estuarine gradient of the northern coast of Pernambuco, in order to evaluate possible temporal and spatial differences in its structure, abundance and ecological indices. The work was carried out at Itamaracá Island, near the mouth of the Jaguaribe River, through monthly collections during an annual cycle, always at low tide during the new moon. Drags were performed using a mangote net with 20 m long, 1.5 m high and 5 mm mesh opening. The drags with replicates were carried out at two points: 1) in the reef zone (marine shore), and 2) in the Jaguaribe River estuary (near the mouth). The individuals collected were euthanized and immersed in Eugenol solution according to the CONCEA, then labeled and fixed in situ in 10% formalin, taken to the laboratory where they were preserved in 70% ethanol, and later identified to the lowest possible taxonomic level. The number of individuals per species was quantified in order to correlate the abundance with spatial-temporal variations. The environmental variables water temperature and salinity were measured in situ at each collection point, using a thermometer and refractometer. The data obtained were analyzed according to species richness, relative abundance (%), through the ecological indices: Margalef's richness, Simpson's dominance, Shannon-Wiener's diversity, and Pielou's equitability. The Chi-square test was performed in order to verify whether there is a significant difference or not between the samples. The nMDS ordination and the ANOSIM test were performed to assess whether there are differences between points and periods of the year. A total of 11,032 individuals were identified, with the Engraulidae family being the most representative (35,57%). The bursting zone was the point of greatest abundance and richness, with 7,795 individuals and 58 species, and the Engraulidae and Polynemidae families were the most representative (50,19%) e (13,30%) respectively, while the estuary presented the Clupeidae and Tetraodontidae families as the most abundant (51,53%) e (14,89%) respectively. Lile piquitinga was the species of greatest abundance, followed by Polydactylus virginicus and Haemulopsis corvinaeformis. The rainy season was responsible for the highest biomass. The site with the highest biomass was the bursting zone, during the dry season. The points showed differences in their composition, abundance and ecological indexes, being estuary the point of greatest dominance (D= 0.29), while the bursting zone presented the greatest Shannon diversity (H= 2.61) and Margalef richness (D= 6.89). Although the subtidal zone presented the highest abundance and the highest diversity, richness and equitability indexes in relation to the estuary, it is evident the great importance of both areas for several fish species in several life stages, being used as breeding and recruitment areas for young fish, showing the importance of the conservation of these regions.