As praias arenosas do Estado do Ceará $b relação entre ambiente físico e a estrutura de comunidade em um ambiente tropical

Abstract

This thesis aimed to study the relationship between benthic macroinvertebrates and physical parameters of 12 sandy beaches of Ceará, in order to recognize physical characteristics, patterns of occurrence and distribution and aspects structuring the benthic community in the studied beaches. Samplings were carried out on the beaches of Redonda, Majorlândia, Canto Verde, Diogo, Iguape, Diários, Pecém, Paracuru, Flecheiras, Preá, Maceió and Bitupitá. Wave height and period, particle size and tide were recorded. Beach profiles, Dean parameter (Ω), Relative Tide Range (RTR) and Beach Index (BI) were calculated to describe morphodynamics. More than 1500 samples of sediments were collected. Benthic macroinvertebrates were later sorted and identified. The density was expressed as ind/m² and community descriptors such as total richness (S), Margalef richness (d), evenness (J) and diversity (H') were calculated. At each beach, and at the sum of all beaches, ordination, clustering and Linktree analyzes were performed. Non-parametric variances (KW) were verified in order to understand variations of species between taxonomic groups, beach types and sectors of the studied beaches. Regression analyzes were carried out between the particle size and the studied beaches, between richness and levels; between particle size and richness of tropical beaches. The species distribution was plotted between the levels of the beach and along Ceará coastline. Bioenv and Linktree routines were assessed to recognize the environmental variables in charge of the distribution of benthic macrofauna. Predictive equations and extrapolative indices like Jacknife1 and Chao 1 were calculated. It was found that Ceará beaches tend to be more dissipative, with gentle slopes and fine grain size. There was a gradient of decreasing grain size, from east to west coast of Ceará. A total of 58 species were recorded in 6064 individuals in 12 beaches studied. Paracuru and Canto Verde presented higher species richness and diversity. Macrofauna species showed different patterns of zonation, at each beach studied, prevailing two zones beaches. Community descriptors increased closer to swash zone. It was observed a typical distribution of molluscs, crustaceans and polychaetes along Ceará coastline. Dominance of crustaceans in the eastern sector (with greater particle size) and polychaetes in the extreme-western sector (finer grain size) were observed. Dissipative beaches had higher similarities in the distribution of macrofauna. The most important physical factors structuring benthic macroinvertebrates were grain size, slope, Beach Index ( BI ) and width of the beach. According to the equations and extrapolative estimators of species richness Ceará beaches are underestimated by more than 50 %. Although the results suggest that Ceará sandy beaches have a benign environment for the establishment of benthic macrofauna, where mid-macrotidals tropical dissipative beaches prevails, species richness was at intermediate values when compared with other tropical beaches.