Influência sazonal na variação espacial de moluscos em estuários da costa semiárida brasileira

Abstract

Estuaries in the semi-arid region of Brazil are dynamic systems characterized by low river discharge, high evaporation, and marine intrusion, leading to seasonal hypersalinity. This study evaluated the spatial and temporal patterns of benthic mollusks in the estuaries of the Choró and Curu rivers (October 2023 to May 2025), with quarterly sampling during dry and rainy seasons, totaling six sampling campaigns. Standardized sampling was conducted using four 20 m transects and 0.25 m2 quadrats, distributed across two sites in the lower zone and two in the upper zone of each estuary, aiming to investigate the effects of salinity on the community. The Curu River estuary exhibited lower average salinity values and less abrupt temporal salinity gradients, which were associated with higher species richness and diversity of mollusks. Species composition varied spatially in both estuaries; however, seasonal variation was significant only in the Curu estuary. Results show that moderate salinity levels (5–18, mesohaline) favor mollusk richness, whereas extremes — such as intense freshwater input or hypersalinity (>40) — significantly reduce benthic diversity.In the Curu estuary, the lower zone, with more stable salinity, supported 16 species, while the upper zone, exposed to freshening, recorded only two. A similar pattern was observed in the Choró estuary, where the upper zone experienced hypersaline conditions and low diversity. These findings suggest that salinity extremes, regardless of direction, act as ecological filters by excluding less tolerant species. Under climate change scenarios, the intensification of droughts and hydrological alterations caused by human activities (e.g., damming) may exacerbate salinization and compromise key habitats such as mangroves, reducing environmental heterogeneity and the availability of refuges for benthic fauna. Therefore, the conservation of estuaries in semi-arid regions requires maintaining intermediate salinity ranges and controlling hydrological disturbances. This study provides an integrated approach, demonstrating how spatial and seasonal factors interact to shape community structure in ecosystems under increasing environmental pressure.