Abstract: Four core samples were collected from the vicinity of Alibey and Maden islands on the northwestern ofAyvalık. 91 sediment samples were obtained from the cores and were analyzed for their recentforaminifer content. High abundance of individuals with morphological abnormalities were observed inbenthic foraminifer species such as, Peneroplis pertusus, P. planatus, Lobatula lobatula, Ammoniacompacta, A. parkinsoniana, Challengerella bradyi, Elphidium complanatum, E. crispum. Theintroduction and deposition of heavy metal with terrestrial origin in marine biota result in anenvironmental risk for aquatic life. Environmental pollution became common mainly in the second halfof 20th century, because of dumping of materials, such as manganese, lead and iron to terrestrial andmarine environments. Also managing the ore beds led to significant morphological changes inforaminiferal assemblages. The abnormal test development observed in foraminifers and presented inthis study are suggested to be the result of biological effects of the heavy metals that reached marineenvironment, and this phenomenon can be used as a practical indicator to determine the naturalenvironmental pollution. The aim of this study is to find out the possible reasons of these morphologicalabnormalities, and compare with other factors which are known to cause similar deformations.