Mercury exposure in relation to foraging ecology and its impact on the oxidative status of an endangered seabird.

Mercury is a natural element extensively found in the Earth's crust, released to the atmosphere and waters by natural processes. Since the industrial revolution, atmospheric deposition of Hg showed a three-to-five-fold enrichment due to human activities. Marine top predators such as seabirds are recognized valuable bioindicators of ocean health and sensitive victims of Hg toxic effects. Hg negatively affects almost any aspect of avian physiology; thus, birds prove valuable to study the effect of Hg exposure in vertebrates. The Black-vented Shearwater is endemic to the North-Eastern Pacific Ocean, where it forages along the Baja California Peninsula during the breeding period. The area has no industrial settlement and is in the southern portion of the California Current System (CCS). After observing possible contamination effects in eggshells, we decided to quantify the exposure of breeding birds to Hg and test for possible effects on oxidative status of the species. The concentration of Hg in erythrocytes averaged 1.84 µg/g dw and varied from 1.41 to 2.40 µg/g dw. Males and females had similar Hg concentrations. The individual trophic level (reflected by δ15N) did not explain Hg exposure. In contrast, individuals foraging inshore had higher Hg concentrations than those foraging more offshore (reflected by δ13C). Shearwaters having higher concentrations of Hg had lower activity of the antioxidant enzyme glutathione peroxidase and showed lower non-enzymatic antioxidant capacity. Levels of plasma oxidative damage, superoxide dismutase and catalase were not associated with Hg. Our results indicate that (i) the foraging habitat is the factor explaining Hg exposure and (ii) there is some evidence for potential harmful effects of Hg exposure to this seabird species of conservation concern. CAPSULE: The foraging habitat is the factor explaining Hg exposure in seabirds and we observed potential harmful effects of Hg exposure in a seabird species of conservation concern.

Trophic ecology drives contaminant concentrations within a tropical seabird community.

To support environmental management programs, there is an urgent need to know about the presence and understand the dynamics of major contaminants in seabird communities of key marine ecosystems. In this study, we investigated the concentrations and trophodynamics of trace elements in six seabird species and persistent organic pollutants (POPs) in three seabird species breeding on Grand Connétable Island (French Guiana), an area where the increase in human population and mining activities has raised concerns in recent years. Red blood cell Hg concentrations in adults were the highest in Magnificent frigatebirds Fregata magnificens (median: 5.6 µg g-1 dw; range: 3.8-7.8 µg g-1 dw) and lowest in Sooty terns Onychoprion fuscatus (median: 0.9 µg g-1 dw; range: 0.6-1.1 µg g-1 dw). Among POPs, dichlorodiphenyldichloroethylene (p,p'-DDE) was the most abundant compound in plasma of Cayenne terns Thalasseus sandvicensis (median: 1100 pg g-1 ww; range: 160 ± 5100 pg g-1 ww), while polychlorinated biphenyls (PCBs) were the most abundant compound class in plasma of Magnificent frigatebirds (median: 640 pg g-1 ww; range 330 ± 2700 pg g-1 ww). While low intensity of POP exposure does not appear to pose a health threat to this seabird community, Hg concentration in several adults Laughing gulls Leucophaeus atricilla and Royal terns Thalasseus maximus, and in all Magnificent frigatebirds was similar or higher than that of high contaminated seabird populations. Furthermore, nestling red blood cells also contained Hg concentrations of concern, and further studies should investigate its potential health impact in this seabird community. Differences in adult trophic ecology of the six species explained interspecific variation in exposure to trace element and POPs, while nestling trophic ecology provides indications about the diverse feeding strategies adopted by the six species, with the consequent variation in exposure to contaminants.

High levels of mercury and low levels of persistent organic pollutants in a tropical seabird in French Guiana, the Magnificent frigatebird, Fregata magnificens.

In the present study, trace elements and persistent organic pollutants (POPs) were quantified from Magnificent frigatebirds (Fregata magnificens) breeding at a southern Atlantic island. Stable isotope ratio of carbon (δ(13)C) and nitrogen (δ(15)N) were also measured to infer the role of foraging habitat on the contamination. For another group from the same colony, GPS tracks were recorded to identify potential foraging areas where the birds may get contaminated. Fourteen trace elements were targeted as well as a total of 40 individual POPs, including organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). The concentration of Hg in the blood was up to 6 times higher in adults (5.81 ± 1.27 µg g(-1) dw.) than in nestlings (0.99 ± 0.23 µg g(-1) dw.). A similar pattern was found for POPs. ∑PCBs was the prevalent group both in adults (median 673, range 336-2801 pg g(-1) ww.) and nestlings (median 41, range 19-232 pg g(-1) ww.), followed by the sum of dichlorodiphenyltrichloroethanes and metabolites (∑DDTs), showing a median value of 220 (range 75-2342 pg g(-1) ww.) in adults and 25 (range 13-206 pg g(-1) ww.) in nestlings. The isotope data suggested that the accumulation of trace elements and POPs between adults and nestlings could be due to parental foraging in two different areas during incubation and chick rearing, respectively, or due to a shift in the feeding strategies along the breeding season. In conclusion, our work showed high Hg concentration in frigatebirds compared to non-contaminated seabird populations, while other trace elements showed lower values within the expected range in other seabird species. Finally, POP exposure was found generally lower than that previously measured in other seabird species.