Zooplâncton da zona de arrebentação de uma praia arenosa tropical: Fortaleza, Nordeste do Brasil

Abstract

Zooplankton is a major component of the fauna of the surf-zone of sandy beaches. These organisms are fundamental components to feed resident fishes, occupying an important position in the food chain of the ecosystem. The aim of this study is to characterize the zooplankton of the surf zone of a sandy tropical beach in Fortaleza, Northeast Region of Brazil, by understanding the taxonomic composition, density variation and influence of abiotic factors on its components. Horizontal subsurface trawls have been performed (300µm) for five minutes and in triplicate during the months of March, April, May, October, November and December 2012. The samples were fixed immediately after collection in 4% formaldehyde solution buffered with 4g. L -1 sodium tetraborate and analyzed in laboratory under a stereomicroscope for identifying and counting the organisms. Besides the biological material it has been obtained information of salinity, water and air temperature, dissolved oxygen, wave height in the surf, speed and direction of winds and rainfall which were inserted into electronic spreadsheets for analysis. Groups of zooplankton have been identify to the lowest taxonomic level possible with representatives as the Phylum Annelida, Arthropoda, Chaethognatha, Chordata, Cnidaria and Mollusca totaling 36 taxa. In the rainy season, the density general average was lower than the dry season, except in Campaign of October, due to a high density of Mysidacea (15.46 org.m -3 ) in high tide (PM). Regarding the tides, the total absolute density of organisms in the High Tide was higher than in low tide (BM) both in the rainy season (PM = 10.86 org.m-3 ; BM = 8.98 org.m-3 ) as in the dry season (PM = 25.75 org.m-3 ; BM = 2.29 org.m-3 ). The richness of holoplankton was higher than the meroplankton in the low tide, high tide and in the rainy and dry periods. The absolute density of holoplankton was also higher than the meroplankton in both periods. Among the Crustacea, Copepods are the most diverse group, and have been represented by the orders Calanoida, Harpacticoida, Poecilostomatoida and Monstrilloida. The Copepods most common were Euterpina acutifrons, Acartia lilljeborgii, Centropages velificatus, Pseudodiaptomus acutus, Temora turbinata and Corycaeus sp. The Principal Component Analysis (PCA) revealed a positive correlation but low among abiotic parameters and density of all campaigns. Rainfall was the variable that had a greater influence on zooplankton (r = 0.311), mainly in March Campaign which rainfall may have influenced the higher densities in this campaign.