Epiphytic foraminiferal community change suggests environmental deterioration of coastal coral reefs

Benthic protists within Atlantic marine ecosystems play a pivotal role in biogeochemical cycles, particularly through calcium carbonate production, which shapes habitat structure and dynamics. Highly sensitive to anthropogenic perturbations, including nutrient enrichment, these organisms often are more responsive than metazoan taxa, underpinning the FoRAM Index as a robust bioindicator and early warning system for ecological stress. This study evaluates the efficacy of these microbenthic sentinels across the Pinaúnas Reef (Itaparica Island, Bahia, Brazil). Samples were collected during dry and wet seasons across three discrete years (2000, 2010, and 2022) to assess temporal dynamics alongside comprehensive physico-chemical measurements. Univariate and multivariate analyses revealed minimal seasonal variability but a pronounced temporal change in Foraminifera by 2022. Notably, FoRAM Indices declined markedly in the most recent sampling period, driven by a relative reduction in symbiont-bearing taxa (especially Amphistegina spp.) and a concurrent increase in opportunistic species ( Elphidium spp. and Ammonia beccarii ). Elevated nitrate and phosphate levels correlated significantly with these assemblage alterations (positively with taxonomic diversity, but negatively with the FoRAM Index), most likely stemming from burgeoning human population pressures and inadequate effluent management. Although the limited number of sampling years limits the extrapolation to continuous temporal trends, the data clearly indicate a functional transition towards a degraded state. Ultimately, these microorganisms appear to prove far more sensitive than conventional water-quality metrics. By integrating cumulative pollution effects over time, they offer an essential early alert to habitat decline.