Seasonal variations, environmental parameters, and standing crop assessment of benthic foraminifera in eastern Bahrain, Arabian Gulf

Abstract

Living benthic foraminifera in a relatively unpolluted site offshore Bahrain in the Arabian Gulf, were studied to determine the seasonal variability of their populations, as well as environmental parameters that may affect their distribution. The maximum foraminiferal density was observed during winter with the assemblages primarily dominated by rotaliids and secondarily by miliolids. The high population is attributed to an increased number of juveniles. A relationship between sediment grain size and the foraminiferal density reveals that juveniles were most abundant on coarse-grained sandy substrate and less abundant on fine-grained substrates. In spring, the foraminiferal density decreased, and the lowest values were observed during summer. The population increased again in autumn with highest juvenile/adult ratios. Moreover, results of relative abundance and species consistency show that Ammonia and Glabratellina are consistent from the shallowest to the deepest station, whereas miliolids occurred only at deeper stations. The numbers of peneroplidae and Elphidium also increased along the depth transect. Environmental characterization reveals that although the site is subject to eutrophication caused by nitrates and sulfates, pollution caused by hydrocarbons and heavy metals is not significant. The assessment of 63 heavy metals showed that none of the metals had concentrations that exceed internationally accepted norms [the devised level of Effect Range-Low], but with high concentration of strontium. The lack of a significant environmental effect of heavy metals is confirmed by the Foraminiferal Abnormality Index of <2%. Likewise, no hydrocarbon contamination was detected in the water or sediment samples. We conclude that the site in Bahrain is not yet adversely affected by human development, and therefore can provide baseline information for future comparison and assessment of foraminiferal assemblages in contaminated zones of the Arabian Gulf.