Malacofauna associada a um recife de arenito no Nordeste do Brasil

Abstract

Natural reefs are important areas for maintaining life in the oceans. In Ceará there are some works that attest to the diversity of the fauna in the region between tides. The Mollusca Phylum is the second largest within the animal kingdom in number of species. Bitupitá is the last beach of the coast of Ceará and the last district of Barroquinha that has a territorial limit with the state of Piauí. The objective of the present work is to identify the molluscs present in the sandstone reef of Bitupitá beach and demonstrate how the species are distributed there, conducting analyzes of abundance and diversity. The data were collected on a reef that has approximately 7 hectares that has been divided into zones. It was defined that all the reef is part of the mesolittoral, because it is entirely inside the area between tides. From this, a subzone was determined with: upper mesolittoral (MS), the innermost portion of the continent, with a higher concentration of fouling molluscs, such as oysters and mussels, green algae were predominant compared to other algae and it is also the area that spends more time uncovered by water; medium mesolittoral (MM), a region with a lower number of fouling molluscs in relation to the first area, and that already has red and brown algae contrasting with the green ones, and finally, lower mesolittoral (MI), region that spends most part of the day submerged, has rhodophytas as a predominant algal species and low concentration of fouling molluscs. 30 samples were analyzed, a total of 4.892 specimens, divided in 4 classes, 42 families and 66 species. The MS area presented the highest average abundance of individuals with 215 ± 145 compared to MM (194 ± 169) and MI (64 ± 63). However, statistically, there was no significant difference between the abundances in the MS and MM areas, and between MM and MI, however a statistically significant difference was observed between MS and MI (ANOVA: F = 3,721, df = 2, p= 0.03738). The Gastropoda class is the most abundant in the entire sandstone reef of Bitupitá, with the Caecidea family being the dominate. The Bivalvia class is in greater number in the medium mesolitoral with the species Sphenia Fragilis being the one of greater representativity. The polyplacophoras are distributed evenly along the reef, with a slight increase in quantity in the upper mesolith. According to the diversity indexes we can affirm that there is a great diversity of species and there is also uniformity in the quantity of species per zone.