Benthic Foraminiferal Response to a Salinity Gradient in the Uqair Hypersaline Lagoonal System, Gulf Coast of Saudi Arabia

Faunal trends within foraminiferal assemblages are documented along a geographical salinity gradient within the Uqair la-goonal system in the Arabian Gulf, east coast of Saudi Arabia. The Arabian Gulf is a salinity-stressed sea characterized by varying salinity conditions, especially in its coastal lagoons. A high salinity gradient is observed in restricted shallow water lagoons at Uqair. The composition and diversity of benthic foraminiferal assemblages show distinct variations along this natural salinity gradient. Key foraminiferal genera such as Quinqueloculina, Ammonia, and Elphidium display a high tolerance to increased salinity, whereas Cycloforina, Pseudo-triloculina and Miliolinella exhibit a more moderate tolerance. Peneroplis, Coscinospira, Monalysidium, and Agglutinella have a lower tolerance and are less abundant at higher salinities. Lachlanella, Pseudolachlanella and Glabratellina show the lowest tolerance and are mostly absent from hypersaline areas. Overall diversity shows a clear negative trend, decreasing markedly along the gradient from “normal” marine to more hypersaline conditions. In contrast, dominance of the most tolerant taxa increases along the gradient. The assemblages may also be influenced by substrate type, as Lachlanella was only found in areas with rocky substrate. Based on these results, Quinquelo-culina can be regarded as a key indicator taxon for hypersaline conditions in this unpolluted lagoonal environment. Our findings provide new insight into the ecological response of benthic foraminifera to naturally stressful hypersaline conditions in the western Arabian Gulf.