Intraspecific Variation in Mercury, δ¹⁵N, and δ¹³C Among 3 Adélie Penguin (Pygoscelis adeliae) Populations in the Northern Antarctic Peninsula Region

Abstract

Mercury (Hg) is a pervasive environmental contaminant that accumulates in the organs and tissues of seabirds at concentrations capable of causing acute or long-term adverse health effects. In the present study, Hg concentrations in Adélie penguin (Pygoscelis adeliae) egg membranes and chick feathers served as a proxy for Hg bioavailability in the marine environment surrounding the northern Antarctic Peninsula. Stable isotopes were measured in conjunction with Hg to infer information regarding feeding habits (δ 15 N, diet/trophic level; δ 13 C, foraging habitat). The Hg concentrations were low relative to toxicity benchmark values associated with adverse health effects in birds and ranged between 0.006 and 0.080 µg g -1 dry weight (n = 65) in egg membranes and 0.140 to 1.05 µg g -1 fresh weight (n = 38) in feathers. Egg membrane δ 15 N signatures suggested that females from different breeding colonies had similar diets consisting of lower and higher trophic prey prior to arrival to breeding grounds. In contrast, δ 15 N signatures in feathers indicated that chick diet varied by colony. The Hg concentrations demonstrated significant positive relationships with δ 15 N, providing support for the hypothesis of Hg biomagnification up the food chain. The δ 13 C signatures in both tissue types provided evidence of foraging habitat segregation among populations. The differences in Hg exposure and foraging ecology suggest that each colony has localized foraging behaviors by breeding adults that warrant additional investigation.

Variation in blood mercury concentrations in brown skuas (Stercorarius antarcticus) is related to trophic ecology but not breeding success or adult body condition

“…An alternative explanation for this, is that skua diet changes according to the phenology and peaks in availability of their prey, and opportunistic changes in consumption of penguin eggs and chicks across the season according to their availability occurs (Graña Grilli et al 2014;Ibañez et al 2022). The increase in δ 15 N values would indicate that with the advance of the season, skuas shift from feeding on penguin eggs to chicks, as the latter display higher levels of Hg (McKenzie et al 2021). RBC δ 13 C values indicated that in both seasons brown skuas had fed on Antarctic prey during the early incubation and pre-laying period.…”

“…Once assimilated, MeHg bioaccumulates within marine organisms and biomagnifies through marine food webs (Bargagli 2008;Driscoll et al 2013). Long-lived, upper trophic level predators, such as many Antarctic seabirds, are therefore potentially exposed to high Hg concentrations through their prey (Bearhop et al 2000;Bargagli 2008;Tavares et al 2013;Mills et al 2020;McKenzie et al 2021).…”

“…Benthic and mesopelagic fish and cephalopods tend to exhibit elevated Hg concentrations, attributed to the increased MeHg production in sediments and at depths associated with low availability of oxygen (Goutte et al 2015;Polito et al 2016;Renedo et al 2020). Some of these species are consumed by seabirds either directly, if they are vertical migrants, or as discards from fisheries, and seabirds can therefore be effective bioindicators of Hg below the photic zone (Carravieri et al 2021;McKenzie et al 2021). Hg contamination of seabirds can show high inter-and intraspecific variation, which is often related to factors including age, sex, latitude and trophic ecology (Monteiro et al 1998;Bearhop et al 2000a, b;Anderson et al 2009;Leat et al 2013;Polito et al 2016;Carravieri et al 2021, Mills et al 2020.…”