Distribuição espacial e temporal do macrozoobentos em manguezais de uma ilha costeira amazônica

Abstract

Mangroves occupy a large part of the Amazon coast and provide several ecosystem services, including high productivity and habitat creation for various species. Benthic macrofauna are an abundant and diverse group in mangroves, whose distribution is influenced by several factors, such as salinity and sediment characteristics, which can be modified by the presence of vegetation. The objective of this study was to describe the spatial and temporal variations of the macrobenthic community of unconsolidated mangrove substrates on the island of Algodoal-Maiandeua, northeast of Pará. Sampling was carried out in two campaigns, one in the dry season (November/2022) and the other in the wet season (May/2023), in mangrove areas of two estuarine channels, Furo da Mocoóca (wider and straighter) and Furo Velho (narrower and more sinuous). In each channel, two collection zones were defined (unvegetated and vegetated). In each zone, four sampling points were identified from which four biological samples (macrozoobenthos) were taken using a cylindrical sampler (10 cm diameter) buried at a depth of 20 cm in the substrate. At the same time, water parameters and sediment were collected. A total of 2,196 individuals were identified, distributed in 85 taxa (species and morphospecies), with the greatest abundance of Annelida. The density and richness of the macrofauna did not vary between channels, but only between zones and periods. In general, the highest values occurred in the non-vegetated zone and in the dry period. The taxonomic and functional structure of the macrofauna varied spatially (channels and zones) and temporally. Spatial variation in macrofauna was associated with substrate characteristics, while seasonal variation was mainly associated with salinity. In the narrower channel, grazing polychaetes and oligochaetes dominated, associated with a muddier substrate with a higher organic content. In the wider channel, predatory forms were more abundant, associated with sandier substrates. In terms of zones, oligochaete taxa, crustaceans and insects were more abundant in the vegetated zone. In the non-vegetated zone, polychaetes (predators and detritivores) were generally dominant. It is likely that the presence of vegetation, while increasing the complexity of the habitat, interferes with the presence of infauna organisms. The rainy season, when the salinity in the estuary decreased significantly, was characterized by a decrease in the richness of the macrofauna and in the density of crustaceans (peracarids), but with an increase in those of Nephtys polychaetes. This study provides important information for understanding the distribution of the macrobenthic community of mangroves on the Amazon coast, considering their interactions with habitat structure and seasonal fluctuations in environmental parameters.