Distribution of benthic foraminifera along the Iranian coast

This study focuses on the distribution of benthic foraminifera along the Iranian coast of the Gulf, extending over 1000 km from the northeast close to Shatt Al-Arab/Arvand Rud to the southeast near the Strait of Hormuz where it connects to the Indian Ocean. The Gulf is a naturally stressed environment due to extremes of salinity and temperature and anthropogenically affected by rapid urbanization, maritime transport, desalination plants, and oil platforms. Historical records and distributional studies have commonly underestimated the benthic foraminiferal diversity in the Gulf. Thirty-two samples collected from depths between 20 and 45 m were analyzed for total (unstained) foraminiferal assemblages. A total of 221 benthic foraminiferal species and subspecies belonging to 69 genera, 34 families, and 6 orders were recognized. The assemblages are dominated by hyaline taxa (49%) and porcelaneous foraminifera (36%), while agglutinated foraminifera represent only a minor part (15%). The ten most abundant species are Nonion sp. 1 (5.8%), Quinqueloculina sp. 1 (4.7%), Asterorotalia dentata (4.2%), Bolivina cf. B. persiensis (3.9%), Asterorotalia sp. 3 (3.5%), Rotalinoides gaimardi (3.4%), Ammonia sp. 1 (3.3%), Quinqueloculina sp. 8 (3.3%), Bolivina cf. B. striatula (3.0%), and Nonion sp. 2 (2.8%). We speculate that increase of finer sediments (mud), availability of nutrients, and the presence of oxygen are factors controlling the diversity and distribution of benthic foraminifera. The current thermal regime in the Gulf has been cited as a model for the tropical ocean in 2090–2099. In light of it, foraminiferal assemblage structure, composition, and distribution may provide an insight into the nature of biotic response to future climate change in the Gulf region under conditions of global warming and a baseline for future comparison within and beyond the Gulf. This study also updates the knowledge on the types and distributions of benthic foraminiferal groups in this poorly known area.