Adélie penguin as bioindicator of mercury concentrations

Since the Industrial Revolution, mercury (Hg) concentrations in the environment have been increasing due to anthropogenic activities. The toxic effect that this metal has on animals and humans led to the adoption of the Minamata Convention on Mercury by more than 140 countries in 2013, to protect human health and the environment. Hg disperses throughout the world through atmospheric currents, depositing even in the most remote places, such as the polar regions.

Seabirds, as top predators, reflect the Hg contamination that is present in their marine food web, through biomagnification processes. Their main form of Hg excretion is through moulting. Within seabirds, the Adelie penguin (Pygoscelis adeliae) (Figure 1) has a set of ideal characteristics to be used as a bioindicator for Hg concentrations in Antarctic food webs, since it has a circumpolar distribution and is the most common and abundant penguin species on the Antarctic continent.

Figura 1 – Adélie penguin (Pixabay).

For the circumpolar assessment of Hg concentrations, feather samples were collected from 538 individuals (490 adults of reproductive age and 48 pre-fledging chicks) between 2005 and 2021 in 24 colonies around the continent. Total mercury (T-Hg) concentrations were evaluated for each sample. Values of the isotopes δ13C and δ15N were also determined on the feathers and used as proxies for the feeding habitat and trophic position of the penguins, respectively.

At the circumpolar level, Hg contamination proved to be relatively homogeneous between the different regions assessed. However, a Hg hotspot was observed in the Ross Sea (Figure 2), associated with a higher trophic position of Adélie penguins, likely due to a higher proportion of fish in their diets.

Figure 2 – Spatial variation in feather Hg concentrations of (a) adult and (b) chick Adélie penguins in 24 Antarctic colonies. The color gradient represents increasing concentrations of Hg. The sample size (n) is indicated by the size of the circles and triangles. The average position of the Polar Front (dashed black line) reflects the northern limit of the Adélie penguin’s distribution.

It is essential to continue monitoring Hg concentrations to assess the effectiveness of the Minamata Convention on Mercury. Large-scale assessments are extremely important to monitor the contamination status of Antarctic food webs over time, and also to assess global trends, taking into account the climate change context.

Author: Sara Santos

Source: Cusset, F., Bustamante, P., Carravieri, A. et al. Circumpolar assessment of mercury contamination: the Adélie penguin as a bioindicator of Antarctic marine ecosystems. Ecotoxicology 32, 1024–1049 (2023).