Distribuição e estrutura das assembleias de Nematoda em três praias arenosas urbanas do Nordeste do Brasil

Abstract

The Nematoda assemblages were investigated with the aim of analyzing a structure and distribution of genera, considering the spatial variation of the horizontal type in three urban sandy beaches in the state of Pernambuco. The collections were carried out in November 2020, on the beaches of Barra de Jangada, Cupe and Itapuama. Two transects per beach were delimited, covering the upper midlittoral (MS), medium (MM), lower (MI) and infralittoral (I) regions. For sampling, a 3.0 cm diameter cylindrical sampler with 10 cm height was used to extract the first 5 cm of the sediment. The collected material was fixed in a 4% saline formalin solution. Additional samples were collected for analysis of particle size parameters, organic matter content, chlorophyll-ɑ and pheopigments. In the laboratory, the samples were washed in running water over geological sieves with a 500 and 44 μm opening, with subsequent extraction, counting, preparation on permanent slides and identification of the organisms at the genus level. The univariate indices of density (ind.10 cm-²), genus richness (S), Shannon diversity (H') and Pielou evenness (J') were calculated and the results compared between beaches, transects and zonations using the 3-factor PERMANOVA, which was also used to verify differences in the community structure of the three beaches. The nMDS was used to represent the significant results of PERMANOVA, SIMPER applied to determine which genera contributed the most to dissimilarities and PCA to analyze the distribution patterns of environmental variables between the beaches. Barra de Jangada had the highest richness (43) and highest mean density (1286.62 ind. 10 cm-2 on the I), followed by Cupe (39) and Itapuama (34), which had the lowest mean density (1.41 ind. 10 cm-2 in MM). With regard to trophic distribution, the greatest heterogeneity occurred in Barra de Jangada, with the largest contributions from organisms 2B (28.40%), Cupe 2A (52.27%) and Itapuama 1B (57.02%). PERMANOVA showed significant differences in univariate indices (S; density; J’; H’) between nematode assemblages from the intertidal region of the three beaches (p<0.001). Theristus was the genus responsible for the greatest contribution of dissimilarity between the beaches of Barra de Jangada and Cupe (8.13%) and Barra de Jangada and Itapuama (7.97%) and the environmental factor that most contributed to the total environmental variability was the particle size. Although these urban beaches are geographically located in the same coastal region, the Nematoda assemblages showed differences between their transects and their zonations. This result can be attributed to the environmental heterogeneity of these beaches, promoted by their distinct morphodynamic characteristics and also the form of use and exploitation of these ecosystems.