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

Abstract

Sea sonal vari a tions, en vi ron men tal pa ram e ters and stand ing crop as sess ment of ben thic foraminifera in east ern Bah rain, Ara bian Gulf Liv ing ben thic foraminifera in a rel a tively un pol luted site off shore Bah rain in the Ara bian Gulf, were stud ied to de ter mine the sea sonal vari abil ity of their pop u la tions, as well as en vi ron men tal pa ram e ters that may af fect their dis tri bu tion. The max i mum foraminiferal den sity was ob served dur ing win ter with the as sem blages pri mar ily dom i nated by rotaliids and sec ond arily by miliolids. The high pop u la tion is at trib uted to an in creased num ber of ju ve niles. A re la tion ship be tween sed i ment grain-size and the foraminiferal den sity re veals that ju ve niles were most abun dant on coarse-grained sandy sub strate and less abundant on fine-grained sub strates. In spring, the foraminiferal den sity de creased, and the low est val ues were ob served dur ing sum mer. The pop u la tion in creased again in au tumn with high est ju ve nile/adult ra tios. More over, re sults of rel a tive abundance and spe cies con sis tency show that Am mo nia and Glabratellina are con sis tent from the shal low est to the deep est station, whereas miliolids oc curred only at deeper sta tions. The num bers of Peneroplidae and Elphidium also in creased along the depth transect. En vi ron men tal char ac ter iza tion re veals that al though the site is sub ject to eutrophication caused by nitrates and sul fates, pol lu tion caused by hy dro car bons and heavy met als is not sig nif i cant. The as sess ment of 63 heavy metals showed that none of the met als had con cen tra tions that ex ceed in ter na tion ally ac cepted norms (the de vised level of Ef fect Range -Low), but with high con cen tra tion of stron tium. The lack of a sig nif i cant en vi ron men tal ef fect of heavy met als is con firmed by the Foraminiferal Ab nor mal ity In dex of <2%. Like wise, no hy dro car bon con tam i na tion was de tected in the wa ter or sed i ment sam ples. We con clude that the site in Bah rain is not yet ad versely af fected by hu man de vel op ment, and there fore can pro vide base line in for ma tion for fu ture com par i son and as sess ment of foraminiferal as sem blages in con tam inated zones of the Ara bian Gulf.

Benthic Foraminifera in Eastern Bahrain: Relationships With Local Pollution Sources

“…The sea floor in the area is characterized by carbonates with fine to coarsegrained sediments. The offshore coastal area is microtidal (<1 m) with a diurnal rhythm [16]. The foreshore is wide and slopes very gently, and is characterized by silty, sandy carbonate sediments.…”

“…The selection of season has been primarily based on our previous findings, where the highest standing crop was found in winter [16]. The bottom water and sediment samples were collected from the coastline to 250 m offshore, from water depths of 0.4 m to 1.0 m. The transect was compared with a nearby one in an unpolluted site previously studied by Arslan et al [16].…”

“…Finally, the entire residue was microscopically analyzed and the total numbers of living foraminifera (both adults and juveniles) were picked under a reflected-light binocular microscope based on the presence of protoplasm. We distinguished visually between "living" (protoplasm-full) and "dead" (protoplasm-empty) as described previously [16,18]. Assemblage parameters including the adult/ juvenile ratio (individuals with diameter less than 150 µm were considered juveniles), foraminiferal density (FD, number of living individuals), and generic diversity indexes (richness, H' and Fisher-α) were calculated.…”

“…Foraminifera were taxonomically identified at the genus level using the monographs of Hottinger et al [19], Loeblich and Tappan [20] and Hayward et al [21]. As the current study attempts to compare the foraminiferal density with the data published by Arslan et al [16], we did not attempt to resolve species taxonomy.…”

“…Based on such criteria, a distinction has been developed to differentiate pollution-tolerant taxa from pollution-sensitive taxa [15]. A previous seasonal survey of living benthic foraminifera in a relatively unpolluted site offshore in eastern Bahrain revealed the maximum foraminiferal density (FD) during the winter season, attributed to an increased number of juveniles [16]. A pronounced seasonality effect in the benthic foraminiferal populations has also been observed.…”