Environmental controls on shallow water benthic foraminifera along Singapore's equatorial urban coastlines

Foraminifera are valuable bioindicators that can help assess the ecological impacts of nutrient enrichment and organic matter loading in rapidly urbanising coastal environments, particularly in Southeast Asia where baseline environmental data remain sparse. Singapore provides a pertinent site to address this gap because its compact coastline encompasses pronounced environmental gradients within an equatorial setting. Monthly water quality and seabed investigation of Singapore's coastal environment from November 2023 – October 2024 identified four environmental regimes, ranging from relatively marine-influenced to persistently eutrophic environments. Notably, while water quality showed pronounced seasonal variability, sediment characteristics and foraminiferal communities exhibit stronger spatial variation, suggesting that they primarily record persistent environmental conditions rather than shorter-term fluctuations. Multivariate analyses show that foraminiferal communities are spatially structured, and are primarily driven by nutrient availability, organic matter enrichment and degree of marine influence. Specifically, increasing nutrient and organic loading are associated with declining diversity, greater dominance of stress-tolerant taxa (e.g., Ammonia veneta ), and disappearance of sensitive taxa (e.g., Elphidium somaense) . This is also evident in the community metrics, where foraminiferal diversity (H′) and Foram Stress Index (FSI) were significantly correlated with water trophic status (TRIX) and sediment total organic carbon. Random Forest modelling further identified organic matter enrichment as primary drivers for Ammonia confertitesta and Elphidium somaense abundance, highlighting their potential as bioindicators for this change. Our findings establish the first modern living foraminiferal baseline record for Singapore, and demonstrate the value of integrating community metrics and taxon-environment relationships to support long-term monitoring of equatorial urban coastal systems.