SEASONAL AND SPATIAL PATTERNS OF ICTIOPLANKTON IN THE BACANGA RIVER ESTUARY, BRAZIL: ENVIRONMENTAL CONTROLS AND CONSERVATION CHALLENGES

Abstract

This study analyzed the spatial-temporal distribution of ichthyoplankton in the Bacanga River Basin, São Luís, Maranhão, an area of notable ecological and economic importance belonging to the Amazon biome, in the urban center of São Luís, MA. Four collection campaigns were carried out between September 2023 and September 2024, covering the dry, transition, and rainy seasons. Fish eggs and larvae were collected with a plankton net at nine estuarine points, with simultaneous measurements of environmental variables such as salinity, temperature, dissolved oxygen, pH, total dissolved solids (TDS), oxidation-reduction potential (ORP), and Eh. Multivariate analyses (MDS, SIMPER, PCA, CCA, and PERMANOVA) were applied to identify distribution patterns associated with seasonal, spatial, and abiotic factors. The results revealed that the abundance and composition of ichthyoplankton were significantly influenced by seasonality and the location of sampling points, with higher abundances in downstream regions and during transition periods. Among the findings were the detection of pigmented eggs and larvae with organic residues, indicating direct anthropogenic impacts, and the presence of Oreochromis niloticus, an exotic species, in areas of lower salinity. The taxa Anchoa sp., Atherinella brasiliensis, Oligoplites saurus, in addition to fish eggs, were the most representative, demonstrating clear associations with physical-chemical variables. It is concluded that the Bacanga basin is a crucial area for fish reproduction and early development, and the data obtained are fundamental to support public policies for fisheries conservation and socio-environmental sustainability, in line with Sustainable Development Goals (SDGs) 6, Clean Water and Sanitation, and 14, Life Below Water.