Bioaccumulation of heavy metals in eggshell and egg content of seabirds: Lesser (Thalasseus bengalensis) and Greater Crested Tern (Thalasseus bergii)

The Persian Gulf, the most important marine ecosystem, and its islands are negatively impacted by development and pollution. Different types of pollution, especially heavy metals in these habitats, may create risks to birds, influencing reproductive performance, survival, and behaviors. Heavy metals (Cd, Pb, Cr) were analyzed in two long-lived and top food web-level sea birds, Lesser (Thalasseus bengalensis) and Greater Crested Tern (Thalasseus bergii). The research was carried out during 2018 on Nakhiloo Island, located in Dayyer-Nakhiloo Marine National Park, northeastern Persian Gulf, Iran. The nests were selected randomly, and 40 eggs of colonially-nesting terns (20 eggs T. bengalensis and 20 eggs T. bergii; a single egg per nest) were collected. The concentration of heavy metals in eggshells and egg contents was studied to investigate whether bioaccumulation varies between the eggshells and egg contents and also varies in both species. There were significant differences in the amounts of Cd between eggshell and egg content in the Greater and Lesser Crested Tern. This difference was not significant in the concentrations of Pb between the eggshell and egg content in the Tern species. Concentration of Cr did not appear to accumulate in the egg content and was below detection limit. There were significant differences in the concentrations of Cd in the eggshells and egg content between the Greater and Lesser Crested Tern. The results serve to improve understanding and to evaluate the dynamics of heavy metals in eggshells and egg content in various avian species.