Mercury exposure in an endangered seabird: long-term changes and relationships with trophic ecology and breeding success

Abstract

Mercury (Hg) is an environmental contaminant which, at high concentrations, can negatively influence avian physiology and demography. Albatrosses (Diomedeidae) have higher Hg burdens than all other avian families. Here, we measure total Hg (THg) concentrations of body feathers from adult grey-headed albatrosses ( Thalassarche chrysostoma ) at South Georgia. Specifically, we (i) analyse temporal trends at South Georgia (1989–2013) and make comparisons with other breeding populations; (ii) identify factors driving variation in THg concentrations and (iii) examine relationships with breeding success. Mean ± s.d. feather THg concentrations were 13.0 ± 8.0 µg g −1 dw, which represents a threefold increase over the past 25 years at South Georgia and is the highest recorded in the Thalassarche genus. Foraging habitat, inferred from stable isotope ratios of carbon ( δ 13 C), significantly influenced THg concentrations—feathers moulted in Antarctic waters had far lower THg concentrations than those moulted in subantarctic or subtropical waters. THg concentrations also increased with trophic level ( δ 15 N), reflecting the biomagnification process. There was limited support for the influence of sex, age and previous breeding outcome on feather THg concentrations. However, in males, Hg exposure was correlated with breeding outcome—failed birds had significantly higher feather THg concentrations than successful birds. These results provide key insights into the drivers and consequences of Hg exposure in this globally important albatross population.

Spatial and sex differences in mercury contamination of skuas in the Southern Ocean

“…This result contrasts with other studies concluding that breeding latitude has a limited effect on Hg contamination of seabirds in waters south of the APF (Cherel et al, 2018;Carravieri et al, 2020). Nonetheless, a pattern of increasing Hg contamination of seabirds from Antarctic waters towards the sub-Antarctic and subtropics is commonly observed in the Southern Hemisphere (Carravieri et al, 2014b(Carravieri et al, , 2016(Carravieri et al, , 2017(Carravieri et al, , 2020Cherel et al, 2018;Mills et al, 2020;Renedo et al, 2020). For instance, blood THg concentrations of skua chicks in the southern Indian Ocean increase from breeding sites in the Antarctic to those in the sub-Antarctic and subtropics, with skuas at Amsterdam Island showing the highest recorded concentrations for seabird chicks globally (3.98 ± 0.77 µg g -1 dw) (Carravieri et al, 2017; Table 3).…”

“…Antarctic marine ecosystems are often considered to be pristine environments, yet wildlife in the polar regions may still be exposed to high levels of environmental contaminants (Ibañez et al, 2020;Mills et al, 2020). This study provides a detailed evaluation of the underlying drivers of blood THg contamination of brown skuas from three breeding colonies located south of the APF in the Antarctic Zone of the Southern Ocean.…”

“…Hg is a neurotoxin and endocrine disruptor (Tan et al, 2009), and contamination may impact various aspects of development, physiology and breeding behaviour in seabirds (Burger and Gochfeld, 1997;Evers et al, 2008;Tartu et al, 2013;Goutte et al, 2015). Hg contamination has also been associated with reduced breeding success (Goutte et al, 2014;Ackerman et al, 2016;Mills et al, 2020). The mean blood THg (dw) concentrations reported here are equivalent to 0.94 µg g -1 wet weight (ww), 0.72 µg g -1 ww and 0.20 µg g -1 ww at Bird Island, Signy Island and Bahía Esperanza/Hope Bay, respectively (assuming a 79% moisture content) (Eagles-Smith et al, 2008;Ackerman et al, 2016).…”

“…Seabirds are effective bioindicators of Hg contamination in marine ecosystems (Monteiro and Furness, 1995;Monteiro et al, 1996;Carravieri et al, 2016). Hg contamination may also negatively impact aspects of seabird behaviour, physiology and development, and can have short-or long-term fitness consequences (Goutte et al, 2014;Ackerman et al, 2016;Mills et al, 2020). Studies of seabird communities in the Southern Ocean, from the Antarctic continent to the subtropics, have demonstrated extensive interspecific variation in Hg contamination (Anderson et al, 2009a;Carravieri et al, 2014a;Becker et al, 2016;Polito et al, 2016).…”

“…Studies of seabird communities in the Southern Ocean, from the Antarctic continent to the subtropics, have demonstrated extensive interspecific variation in Hg contamination (Anderson et al, 2009a;Carravieri et al, 2014a;Becker et al, 2016;Polito et al, 2016). Hg contamination of seabirds also often differs among conspecifics, and this variation may be driven by factors such as age, sex, breeding status and trophic ecology (Bearhop et al, 2000a;Polito et al, 2016;Mills et al, 2020). Moreover, several studies, mostly undertaken in the Indian Ocean sector of the Southern Ocean, have demonstrated that Hg contamination is lower for seabirds feeding in Antarctic compared to sub-Antarctic and subtropical waters (Carravieri et al, 2014b(Carravieri et al, , 2016(Carravieri et al, , 2017(Carravieri et al, , 2020Cherel et al, 2018;Mills et al, 2020;Renedo et al, 2020).…”