Carryover effects of winter mercury contamination on summer concentrations and reproductive performance in little auks

Mercury contamination and potential health risk to French seabirds: A multi-species and multi-site study

Mercury (Hg) is a naturally occurring highly toxic element which circulation in ecosystems has been intensified by human activities. Hg is widely distributed, and marine environments act as its main final sink. Seabirds are relevant bioindicators of marine pollution and chicks are particularly suitable for biomonitoring pollutants as they reflect contamination at short spatiotemporal scales. This study aims to quantify blood Hg contamination and identify its drivers (trophic ecology inferred from stable isotopes of carbon (δ13C) and nitrogen (δ15N), geographical location, chick age and species) in chicks of eight seabird species from 32 French sites representing four marine subregions: the English Channel and the North Sea, the Celtic Sea, the Bay of Biscay and the Western Mediterranean. Hg concentrations in blood ranged from 0.04 μg g-1 dry weight (dw) in herring gulls to 6.15 μg g-1 dw in great black-backed gulls. Trophic position (δ15N values) was the main driver of interspecific differences, with species at higher trophic positions showing higher Hg concentrations. Feeding habitat (δ13C values) also contributed to variation in Hg contamination, with higher concentrations in generalist species relying on pelagic habitats. Conversely, colony location was a weak contributor, suggesting a relatively uniform Hg contamination along the French coastline. Most seabirds exhibited low Hg concentrations, with 74% of individuals categorized as no risk, and < 0.5% at moderate risk, according to toxicity thresholds. However, recent work has shown physiological and fitness impairments in seabirds bearing Hg burdens considered to be safe, calling for precautional use of toxicity thresholds, and for studies that evaluate the impact of Hg on chick development.

Metals and other trace elements in plasma and feathers of seabirds breeding in Svalbard

We assessed the concentrations of metals and other trace elements in two of the most common seabird species breeding on Svalbard, the black-legged kittiwake (Rissa tridactyla) and the Brünnich's guillemot (Uria lomvia). Both of these species feed mostly on fish and crustaceans but have different foraging strategies, kittiwakes being surface feeders while guillemots are divers. We investigated the concentrations of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), lead (Pb), selenium (Se) and zinc (Zn) in the plasma and body feathers of black-legged kittiwakes (n = 17), as well as in the body feathers of Brünnich's guillemots (n = 13). Samples were collected from adult birds at two time points, one week apart during July 2017 in Kongsfjorden, Svalbard. Of the non-essential trace elements, As was found at the highest median concentration at both the first (56.23 ng/g ww) and second (39.99 ng/g ww) sampling timepoints in the kittiwake plasma. When separating for the sexes, as well as sampling time, males sampled at the first sampling time point had significantly higher concentrations of As (median at 0.087 ng/g versus 0.039 ng/g) and Se (median 0.26 ng/g versus 0.16 ng/g) compared to males sampled at the second time point. There was no significant difference in plasma concentrations between females at first and second sampling time points. Kittiwake feathers contained significantly higher concentrations of As, Cd and Hg than guillemot feathers, while guillemot feathers had significantly higher concentrations of Cu, Pb and Zn. However, of the non-essential elements in both kittiwake and guillemot feathers Hg was found with the highest median concentrations at 5160 and 1080 ng/g, respectively, thus in kittiwakes exceeding the level of 5000 ng/g associated with adverse effect (e.g., impaired reproduction). Levels of Hg and Se found in the kittiwake feathers were higher than previous studies on seabirds in the Arctic.

Spatial variation of mercury contamination in yellow-legged gulls (Larus michahellis) in the Western Mediterranean

Mercury (Hg) is a global pollutant of major concern in marine and coastal environments. In the Mediterranean Sea, Hg concentrations in biota are higher than in other seas, even when seawater concentrations are similar. Seabirds, as marine top predators, can reflect Hg contamination on a large spatial scale. By sampling seabirds at 17 different breeding colonies, we evaluated Hg concentrations of yellow-legged gulls (Larus michahellis) in the occidental Mediterranean basin in 2021 and 2022. More specifically, we investigated spatial variation of Hg contamination in both chicks and adults as well as associated toxicological risks through the use of blood and feathers, which reflect contamination over different periods of the year. The highest concentrations in chicks were found in Djerba (Tunisia) with blood Hg values of (mean ± SD) 1.69 ± 0.51 μg g-1 dry weight (dw). Adults were most contaminated in Djerba and Dragonera (Balearic Islands, Spain) with blood Hg concentrations of respectively 3.78 ± 2.54 and 5.25 ± 3.73 μg g-1 dw. Trophic ecology was investigated using stable isotope analyses (δ13C, δ15N and δ34S as proxies of feeding habitat and diet), and showed that spatial variation in Hg was mainly driven by foraging habitat in both chicks and adults. Low Hg concentrations were related to the use of anthropogenic food sources. An effect of colony location was also found, suggesting spatial differences in local environmental pollution transfer up to seabirds. Our results also supported the use of δ34S to discriminate between marine and continental foraging habitats in generalist seabirds. This study provides new insights onto the spatial distribution of Hg contamination in a widespread seabird, reporting some of the highest Hg values recorded for this species. Populations with highest concentrations are of potential concern regarding toxicological risks.

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

An important provision of the Minamata Convention on Mercury is to monitor and evaluate the effectiveness of the adopted measures and its implementation. Here, we describe for the first time currently available biotic mercury (Hg) data on a global scale to improve the understanding of global efforts to reduce the impact of Hg pollution on people and the environment. Data from the peer-reviewed literature were compiled in the Global Biotic Mercury Synthesis (GBMS) database (>550,000 data points). These data provide a foundation for establishing a biomonitoring framework needed to track Hg concentrations in biota globally. We describe Hg exposure in the taxa identified by the Minamata Convention: fish, sea turtles, birds, and marine mammals. Based on the GBMS database, Hg concentrations are presented at relevant geographic scales for continents and oceanic basins. We identify some effective regional templates for monitoring methylmercury (MeHg) availability in the environment, but overall illustrate that there is a general lack of regional biomonitoring initiatives around the world, especially in Africa, Australia, Indo-Pacific, Middle East, and South Atlantic and Pacific Oceans. Temporal trend data for Hg in biota are generally limited. Ecologically sensitive sites (where biota have above average MeHg tissue concentrations) have been identified throughout the world. Efforts to model and quantify ecosystem sensitivity locally, regionally, and globally could help establish effective and efficient biomonitoring programs. We present a framework for a global Hg biomonitoring network that includes a three-step continental and oceanic approach to integrate existing biomonitoring efforts and prioritize filling regional data gaps linked with key Hg sources. We describe a standardized approach that builds on an evidence-based evaluation to assess the Minamata Convention's progress to reduce the impact of global Hg pollution on people and the environment.

Sex- and age-specific mercury accumulation in a long-lived seabird

Mercury levels in the environment are increasing, such that they are also expected to accumulate in top-predators, but individual-based longitudinal studies required to investigate this are rare. Between 2017 and 2023, we therefore collected 1314 blood samples from 588 individual common terns (Sterna hirundo) to examine how total blood mercury concentration changed with age, and whether this differed between the sexes. Blood mercury concentrations were highly variable, but all exceeded toxicity thresholds above which adverse health effects were previously observed. A global model showed blood mercury to be higher in older birds of both sexes. Subsequent models partitioning the age effect into within- and among-individual components revealed a linear within-individual accumulation with age in females, and a decelerating within-individual accumulation with age in males. Time spent at the (particularly contaminated) breeding grounds prior to sampling, as well as egg laying in females, were also found to affect mercury concentrations. As such, our study provides evidence that male and female common terns differentially accumulate mercury in their blood as they grow older and calls for further studies of the underlying mechanisms as well as its consequences for fitness components, such as reproductive performance and survival.

Mercury Concentrations in Feathers of Albatrosses and Large Petrels at South Georgia: Contemporary Patterns and Comparisons with Past Decades

Mercury (Hg) is an environmental contaminant that can negatively impact the health of humans and wildlife. Albatrosses and large petrels show some of the highest levels of Hg contamination among birds, with potential repercussions for reproduction and survival. Here, body feather total Hg (THg) concentrations were determined in breeding adults of five species of albatrosses and large petrels in the foraging guild at South Georgia during the mid-2010s. We tested the effects of species, sex and trophic ecology (inferred from stable isotopes) on THg concentrations and compared our results with published values from past decades. Feather THg concentrations differed significantly among species (range: 1.9-49.6 µg g-1 dw), and were highest in wandering albatrosses Diomedea exulans, intermediate in black-browed albatrosses Thalassarche melanophris and northern giant petrels Macronectes halli, and lowest in southern giant petrels M. giganteus and white-chinned petrels Procellaria aequinoctialis. Females were more contaminated than males in all species, potentially due to differences in distributions and diet composition. Across species, THg concentrations were not correlated with feather δ13C or δ15N values, implying that species effects (e.g., breeding and moulting frequencies) may be more important than trophic effects in explaining feather THg concentrations in this foraging guild. Within species, the only significant correlation was between THg and δ13C in wandering albatrosses, which could reflect higher Hg exposure in subtropical waters. Comparisons with THg concentrations from past studies, which reflect contamination from 10 to > 60 years ago, revealed considerable annual variation and some evidence for increases over time for wandering and black-browed albatrosses since before 1950 and from the late 1980s, respectively.

Spatial distribution of selenium-mercury in Arctic seabirds

Mercury (Hg) is a metallic trace element toxic for humans and wildlife that can originate from natural and anthropic sources. Hg spatial gradients have been found in seabirds from the Arctic and other oceans, suggesting contrasting toxicity risks across regions. Selenium (Se) plays a protective role against Hg toxicity, but its spatial distribution has been much less investigated than that of Hg. From 2015 to 2017, we measured spatial co-exposure of Hg and Se in blood samples of two seabird species, the Brünnich's guillemot (Uria lomvia) and the black-legged kittiwake (Rissa tridactyla) from 17 colonies in the Arctic and subarctic regions, and we calculated their molar ratios (Se:Hg), as a measure of Hg sequestration by Se and, therefore, of Hg exposure risk. We also evaluated concentration differences between species and ocean basins (Pacific-Arctic and Atlantic-Arctic), and examined the influence of trophic ecology on Hg and Se concentrations using nitrogen and carbon stable isotopes. In the Atlantic-Arctic ocean, we found a negative west-to-east gradient of Hg and Se for guillemots, and a positive west-to-east gradient of Se for kittiwakes, suggesting that these species are better protected from Hg toxicity in the European Arctic. Differences in Se gradients between species suggest that they do not follow environmental Se spatial variations. This, together with the absence of a general pattern for isotopes influence on trace element concentrations, could be due to foraging ecology differences between species. In both oceans, the two species showed similar Hg concentrations, but guillemots showed lower Se concentrations and Se:Hg than kittiwakes, suggesting a higher Hg toxicity risk in guillemots. Within species, neither Hg, nor Se or Se:Hg differed between both oceans. Our study highlights the importance of considering Se together with Hg, along with different species and regions, when evaluating Hg toxic effects on marine predators in international monitoring programs.

The consumption of ice-derived resources is associated with higher mercury contamination in an Arctic seabird

Sea ice plays a fundamental role in Arctic marine environments, by driving primary productivity and sustaining ice-associated ecosystems. Simultaneously, sea ice influences the contamination of Arctic marine organisms, by modifying contaminant cycles or their bioavailability. Changes in sea ice conditions could therefore profoundly impact the functioning of Arctic marine food webs and their contamination. Top predators such as seabirds, which are subject to bioaccumulation and biomagnification of contaminants, are particularly exposed. In this context, the present study aims to investigate the influence of sea ice and of the use of ice-derived resources on the contamination of seabirds by mercury (Hg). To this end, eggs of thick-billed murres (Brünnich's guillemots, Uria lomvia; n = 60) were collected on Prince Leopold Island (Canadian High Arctic) during four years of varying ice conditions (2010-2013). Trophic tracers (i.e., Highly Branched Isoprenoids, HBIs - an indicator of the use of ice-derived resources; carbon and nitrogen stable isotopes - indicators of foraging habitats and trophic status), as well as total Hg concentrations were quantified. Results showed that feeding on ice-derived resources (as indicated by HBI concentrations) was positively correlated to sea ice cover, and both positively influenced Hg concentrations in murre eggs. However, when testing for the best predictor with model selection, sea ice concentration only drove Hg contamination in murres. This work provides new insights into the role of sea ice and ice-derived resources in the contamination by Hg of Arctic wildlife. Further research is now needed to better understand the relationship between sea ice and Hg contamination in Arctic biota and its underlying mechanisms, but also to identify Hg sources in rapidly changing environmental conditions in the Arctic.

Keystone seabird may face thermoregulatory challenges in a warming Arctic

Climate change affects the Arctic more than any other region, resulting in evolving weather, vanishing sea ice and altered biochemical cycling, which may increase biotic exposure to chemical pollution. We tested thermoregulatory impacts of these changes on the most abundant Arctic seabird, the little auk (Alle alle). This small diving species uses sea ice-habitats for foraging on zooplankton and resting. We equipped eight little auks with 3D accelerometers to monitor behavior, and ingested temperature recorders to measure body temperature (Tb). We also recorded weather conditions, and collected blood to assess mercury (Hg) contamination. There were nonlinear relationships between time engaged in different behaviors and Tb. Tb increased on sea ice, following declines while foraging in polar waters, but changed little when birds were resting on water. Tb also increased when birds were flying, and decreased at the colony after being elevated during flight. Weather conditions, but not Hg contamination, also affected Tb. However, given our small sample size, further research regarding thermoregulatory effects of Hg is warranted. Results suggest that little auk Tb varies with behavior and weather conditions, and that loss of sea ice due to global warming may cause thermoregulatory and energic challenges during foraging trips at sea.