Eastern Mediterranean Quaternary benthic foraminifera: Assessing the interplay between trace metal contamination, biodiversity, and test abnormalities in the Antalya Gulf (Kızılağaç–Gazipaşa, Türkiye)

Shallow littoral environments in dynamic coastal basins undergo complex interactions between natural hydrodynamic regimes and anthropogenic trace element inputs. This study provides an integrated lithostratigraphic, quantitative ecological, and bio-monitoring assessment of modern marine sediments across 15 coastal locations in the Antalya Gulf (Eastern Mediterranean, Türkiye). Pre-Quaternary basement units are unconformably overlain by five distinct Quaternary depositional units. To account for abundance variations in naturally depauperate littoral sites, biodiversity indices (Simpson, Margalef, Pielou) were derived directly from 1 g dry sediment-normalized datasets. Across the coastline, 95 benthic foraminiferal species were identified, with diversity indices peaking in northwestern zones and declining toward the southeast. The Lessepsian immigrant Amphistegina lobifera Larsen, 1976 dominated across most locations, whereas Peneroplis de Montfort, 1808 thrived in high-salinity micro-environments. Severe test discoloration (HCT) directly aligned with dark-colored, Fe-enriched sediments and site-specific trace metal accumulation (e.g., Cr, Ni, Cu, As). However, statistical analysis revealed no significant linear correlation between Fe content and Foraminiferal Abnormality Indices (FAI) ( r = 0.175, p = 0.888 > 0.05, n = 3), confirming that Fe enrichment primarily acts as a geochemical driver of test darkening rather than a direct trigger for structural deformities. Consequently, while benthic foraminifera serve as sensitive bio-indicators of sediment degradation, overall biodiversity indices remain governed by natural littoral hydrodynamics rather than direct trace metal stress. This integrated foraminiferal-geochemical framework offers a transferable tool for coastal quality monitoring across stressed Mediterranean ecosystems.