Influència de Factors Biològics i Ecotoxicològics en el Fracàs Reproductor del Xarrà Comú al Delta de l'Ebre: Nutrients, Contaminants i Biomarcadors de Resposta.

With this Research Project, we will try to cover, in a general way, several external aspects, mainly linked with the diet, which can have an influence on the reproductive success of Common Tern (Sterna hirundo) in the Ebro delta. With this objective, data obtained from two colonies of this species will be compared in addition to data that will be obtained from other three similar species (S. albifrons, S. sandvicensis and Gelochelidon nilotica). Blood samples from adult individuals and eggs (whether viable ones or whether unhatched ones) will be the samples to study. The parameters analyzed in all of them will be the levels of organochlorine residues, which include pesticides and polychlorinated biphenyls (foccussing special attention in the most toxic PCBs congeners, the coplanar group) and the levels of methylmercury (only in eggs). Moreover, this reserve will achieve the determination of the presence of micronuclei in eritrocites and the analysis of the fatty acid and amino acid composition (in eggs and blood). The data obtained from these three last analysis will be proved as biomarkers of response to natural environmental exposition of environmental contaminants and it will be also evaluated the composition and concentration of fatty acids and amino acids as factors that can have some influence on the reproduction