BENTHIC FORAMINIFERA IN THE ARABIAN GULF: REVEALING UNEXPECTED DIVERSITY IN AN EXTREME ENVIRONMENT

The Arabian Gulf is an extreme marine environment characterized by high temperatures, hypersalinity, and limited water exchange with the open ocean. Conventional wisdom suggests such conditions should restrict biodiversity, yet our regional synthesis of 60 years of benthic foraminiferal studies reveals an unexpectedly high diversity of 753 species from 236 genera. This diversity estimate is comparable to temperate and subtropical regions, despite the Gulf's relatively shallow depths and restricted environmental conditions. Our comprehensive taxonomic inventory highlights the Gulf's unique biodiversity resulting from its complex oceanography and environmental heterogeneity. Distinct geographical trends emerge, with the highest diversity (462 species) concentrated in the northwestern deltaic region influenced by fluvial input. In contrast, the extreme hypersaline embayments of the southeastern Gulf host the lowest diversity (93 species) dominated by robust porcelaneous taxa. The agglutinated foraminiferal fauna is depauperate across the Gulf, likely due to the paucity of terrigenous sediments and limited depth gradients. The elevated diversity may result from the interplay of regional extremes promoting genetic isolation and rapid diversification, coupled with propagule dispersal from the oligotrophic Indian Ocean reseeding disturbed populations. However, the true diversity is certainly underestimated due to inadequate sampling of some regions and microhabitats, difficulties with species identification, and the widespread use of open nomenclature for taxonomically problematic groups.This first-ever regional synthesis highlights the Arabian Gulf as an ideal natural laboratory for studying biodiversity origins and maintenance in extreme environments relevant to predicted climate change scenarios. Our checklist provides a critical baseline for tracking biodiversity changes and constitutes a valuable resource for paleoenvironmental, biomonitoring, and conservation studies in this globally significant region.