Efeito da abertura de malha de peneiras na descrição da macrofauna bentônica estuarina em experimentos in situ de eutrofização e recolonização

Abstract

The present work analyzed methodological criteria such as the choice of mesh opening influences the description of estuarine benthic macrofauna experimentally exposed to two sources of impact (1) after a simulated hypoxia event, leading to defaunation of the area (2) after eutrophication of sediment with inorganic nutrients. Data were collected on a muddy tide plain in the estuary of the Santa Cruz canal, Itamaracá, Pernambuco. The sediment was defaunated after cover with black canvas for 70 days and recolonization by macrofauna was monitored over 5 months. In the Eutrophication experiment, two distinct dosages of inorganic nutrients (NPK) (High Dose and Low Dose) were used, applied weekly over 4 months. In the defaunation experiment, the total abundance of macrofauna was 9,302 individuals, distributed in 27 taxons, with Naididae being the most abundant (77% in the combined mesh and 63% in the 0.5mm mesh) followed by Laenereis acuta (14% and 26%, respectively). In the eutrophication experiment a total of 27,140 organisms were collected and distributed in 27 taxons.The most abundant taxon in the combined mesh was Naididae (50%) and L. acuta (31%), similarly to that observed in the 0.5mm mesh (43% and 35%,, respectively). The defaunation experiment analyzed in the 0.5mm mesh showed low diversity (H'= 0.55) highlighting that the material retained in the combined sieves (H'= 0.74) is important in this type of experiment, as it brings better accuracy of the taxons. The results showed that different methodologies present significant differences in community attributes (e.g., composition, diversity, richness and abundance). The results showed the same temporal pattern using different mesh openings, but with recovery on different days. While the 0.5mm mesh showed recovery only on day 153, the combined sieve showed recovery on day 93rd. Regardless of the types of mesh, the SIMPER analysis showed that the differences between the treatments of the Defaunation and Eutrophication experiments, with their respective control areas, were caused by the reduction and/or absence of species, mainly caused by Annelida. With PERMANOVA, differences were detected between defaunated treatments and days, while in the treatment of Eutrophication there was only difference between the high and low dosage treatments on the final days (91st and 118th). The pattern observed, through the MDS, showed separation between Eutrophication treatments over time using combined mesh; such differences were not detected with the use of only one mesh. In the Defaunation experiment, the results were similar between the meshes. Thus, the results confirmed that the methodological procedures (mesh opening) influence the description of the macrobenthic community in experimental studies of defaunation and eutrophication in estuarine environments.