Diatom assemblages in coral patches of the Northwestern Persian Gulf: Community structure across substrates and proximity to oil sites

Abstract

Diatoms, essential primary producers in coral reef ecosystems, are highly sensitive to environmental changes, making them effective bioindicators of ecosystem health. This study investigates diatom assemblages in northwestern Persian Gulf coral reefs, comparing communities in oil-polluted sites around Kharg Island with those in less-impacted conditions near Khargoo Island. A total of 86 diatom taxa from 37 genera were identified across live and dead coral tissues and coral rubble. The most abundant species across all samples (average ± SD) were Halamphora coffeiformis (8.43 ± 1.4 %), Nitzschia dissipata (5.94 ± 2.11 %), and H. borealis (5.75 ± 1.39 %). Statistical analyses revealed that substrate type significantly influenced species richness, with dead corals hosting more diatom species than live corals and coral rubble. While no significant difference in species richness was observed between the oil-polluted and control sites, the assemblages differed compositionally. Diatom communities growing on living corals from the polluted site showed the highest level of within-group dissimilarity, which may indicate habitat instability and a state of dysbiosis. These findings suggest that community differences may be associated with chronic oil exposure, and that substrate type plays an important role in shaping diatom communities. The results also signal the potential of certain diatom species as indirect bioindicators responding not only to the pollutants present at the sampling location but also to the condition of a possibly more sensitive host. Further research is needed to assess the long-term effects of oil pollution on coral reef health and diatom-coral interactions.