Benthic foraminifera as indicators of pollution by heavy metals in the eastern Mediterranean Sea

Benthic foraminifera have been investigated and used for the first time to assess the impact of pollution especially by heavy metals, in a part of eastern Mediterranean Sea From the study a total of 168 benthic foraminiferal species belonging to 75 genera and 35 families has been identified. The dead specimens where used for taxonomic purposes and as a base line against which the deformed forms can be compared. The majority are essentially shallow water species with few deep water forms. The Rotaliina represents the highest percentage of the assemblage followed by the Miliolina, whereas the Lagenina and the agglutinated forms constitute the lowest percentage in the study area. There was a clear seasonality in benthic foraminiferal populations reflected in the reduction of foraminiferal abundance, species diversity and number of species in winter compared to spring assemblages. By observing the changes in foraminiferal populations from contaminated sites and comparing these with populations from noncontaminated sites, inferences regarding the impact of pollution on the environment can be drawn. Changes in foraminifera populations expressed in their abundance, diversity, and richness, particularly when compared with populations from relatively noncontaminated sites suggest changes due to pollution, rather than effects of oceanographic parameters such as temperature, salinity, pH, dissolved oxygen. These parameter are generally seen to be relatively constant within the study area. Only parameters such as depth, type of substrate and heavy metals concentration in the sediments have a clear effect on the distribution of certain species. For example, Ammonia tepida. distribution is effected by depth and heavy metals concentration. On the other hand Asterigerinata mamilla doesn't show any preference to water depth and Amphistegina lobifera shows a preference to the type of substrate and the change in heavy metals concentration rather than to depth. Species considered sensitive to heavy metal pollution such as: Ammonia tepida, Amphistegina lobifera and Peneroplis pertusus are dominant in the contaminated sites and represent the highest percentage of morphological deformations. Analysis of available data, showed that two types of morphological deformations could be distinguished and have been categorised or grouped into mechanical and chemical deformations. Chemical deformation is here interpreted as due to ionic exchange resulting in high Mg/Ca ratios. Mechanical deformation includes: the presence of more than one aperture, the presence of residual chambers. On the other hand, the presence of scars and specimens exhibiting fragment extensions are interpreted as predominantly due to physical abrasion and are completely unrelated to the effect of pollution. The chemically induced deformations, on the other hand, include: abnormal chamber enlargement, distorted chambers and overall test outline, lopsided pseudo-high trochospiral test and lopsided low trochospiral test whorl etc. These have been interpreted as due mainly to pollution caused by increasing heavy metal such as Cadmium, Lead, Zinc, Arsenic, Cobalt, Chromium, Lithium, and Vanadium above threshold values