Assessment of environmental health based on a complementary approach using metal quantification, oxidative stress and trophic ecology of two gull species (Larus michahellis & Larus audouinii) breeding in sympatry

Acknowledgements : We would like to thank the Instituto da Conservação da Natureza e Florestas (ICNF) for permits and logistical support (lodging) to conduct this work. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed and all necessary approvals have been obtained by the ICNF. Special thanks to the wardens, Paulo Crisóstomo and Eduardo Mourato (Reserva Natural das Berlengas) and Silverio (Parque Natural da Ria Formosa). We would like to thank José Seco for valuable inputs during earlier drafts of the manuscript. FRC, LMFA, JGC, ACN, VHP and SCN acknowledge their grants (SFRH/BPD/95372/2013, SFRH/BD/122082/2016, PD/BD/ 127991/2016, SFRH/BPD/108197/2015, SFRH/BPD/85024/2012, SFRH/BPD/94500/2013, respectively) attributed by the Foundation for Science and Technology (FCT; Portugal) and the European Social Fund (POPH, EU). This study benefited from the strategic program of MARE, financed by FCT (MARE - UID/MAR/04292/2020) and financial support provided by FCT and MARE through the project ECOLIND – Seabirds and fish as ecological indicators of contaminants and health in the North Atlantic relevant to ocean resources assessment (MFM/2017/0003).

Metal pollution is currently a major issue in marine ecosystems, as organisms, and particularly seabirds, are exposed and accumulating increased levels from several anthropogenic sources. A set of 13 metals were quantified in two gull species breeding in sympatry, and in two distinct colonies separated by ca. 400 km. Oxidative stress was measured, and stable isotope analyses were used to link metal contamination and oxidative stress with the trophic ecology of each species/population. There was a clear segregation of metal contamination between the two species and to a much lesser extent between colonies. Overall, Audouin's gull was the most contaminated species for most metals, once this species relies mainly on fish and other marine resources. The Yellow-legged gull feeds regularly on terrestrial food sources besides fish, which may dilute contamination levels. Oxidative stress responses were related with birds' trophic ecology and foraging habitat, but apparently not with metal contamination.

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