How can the health of seagulls indicate the health of the oceans?

MARE researchers Ivo dos Santos, Vítor Paiva, Ana Norte, Filipe Ceia, Joana Pais de Faria, Jorge Pereira, Lara Cerveira, Maria Laranjeiro, Sara Veríssimo and Jaime Ramos are co-authors of the article ‘Assessing the impacts of trace element contamination on the physiology and health of seabirds breeding along the western and southern coasts of Portugal’.  The research that led to the article was based on analysing the blood of seagulls and shearwaters to identify the concentration of trace elements such as mercury, selenium and lead.

Marine ecosystems are increasingly subject to the consequences of human activities. Among the growing threats of anthropogenic origin are the effects of overexploitation of metal ores for activities such as metallurgy or construction, which release trace elements such as mercury, selenium and lead into the marine environment. These elements infiltrate trophic chains through different mechanisms: through adsorption on suspended particles or dissolved organic matter, through their absorption by microorganisms and phytoplankton, or directly from the water through gills and skin, accumulating in the bodies of various marine species.

Seabirds are often used as indicators of the state of health of marine ecosystems due to their vulnerability to contamination from human activities. Within this group of animals, coastal seabirds stand out as being highly vulnerable to trace element contamination, due to their proximity to anthropogenic activities such as growing urbanisation and the increase in the number of fishing boats, which have contributed to the increased release of elements into their foraging habitats (e.g. cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn)). Despite this, our understanding of how these contaminants affect the physiology of these birds is still scarce, and there is uncertainty about their vulnerability and tolerance to environmental contamination of this kind.

To this end, a team of researchers including several members of MARE quantified the presence of these trace element contaminants in the blood of gulls (Yellow-legged Gull Larus michahellis and Audouin's Gull Ichthyaetus audouinii ) and shearwaters (Cory's Shearwater Calonectris borealis) belonging to five breeding colonies along the Portuguese coast.

This analysis showed that the concentrations of mercury and lead in the blood of these birds exceeded the toxicity limits in 25% and 13% of the individuals, respectively, making them an ecotoxicological concern, especially since high concentrations of mercury, together with selenium, are associated with a decrease in the sedimentation rate of red blood cells and their greater immaturity. Despite this, the proportions of selenium in relation to mercury suggest that these species may be protected from mercury toxicity. Analyses of the concentration of stable isotopes of carbon and nitrogen also showed that the variation in the concentration of trace elements in the animals‘ blood varies according to the location of the colony and, consequently, the seabirds’ foraging habits.

This study represents a significant contribution to our understanding of blood contamination by trace elements in coastal and oceanic seabirds, and shows that constant monitoring will be necessary due to the potentially dangerous concentrations of these elements.

To access the article click HERE