Interspecific variation of essential and non-essential trace elements in sympatric seabirds.

Chemical pollution is a growing issue for ocean ecosystems, threatening especially apex predators because they bioaccumulate persistent chemical pollutants such as non-essential trace elements. The trophic position is thus a key aspect when assessing the impacts of environmental pollution in marine organisms. Here we investigate the differences in the concentrations of essential (Cu, Cr, Se, and Zn) and non-essential elements (Hg, Al, As, Cd, and Sr), in muscular and hepatic tissues of four sympatric non-migratory seabirds (namely Sula leucogaster, Larus dominicanus, Fregata magnificens, and Thalasseus acuflavidus), which were found stranded along the Brazilian coast. The observed hepatic and muscular interspecific differences in elemental concentrations indicated that these sympatric seabirds are differently exposed to persistent contaminants circulating in the food web due to differences with respect to known feeding behaviours and prey preferences. Moreover, we found a consistent co-accumulative relationship between Se and Hg molar levels in liver tissues with mean Se:Hg molar ratio above 1. This relationship supports previous studies indicating that Se, via the formation of SeHg complexes, plays an essential biochemical role in the detoxification process of methyl mercury in seabirds. Our results suggest that feeding behaviour is an important factor associated to the interspecific differences of trace element concentrations in seabirds. However, traits other than feeding preferences (e.g. age) may also play an important role in the accumulation of these elements.