Mercury biomagnification in the food web of Agami Pond, Kaw-Roura Nature Reserve, French Guiana.

Freshwater ecosystems are among the most important ecosystems worldwide, however, over the last centuries, anthropogenic pressures have had catastrophic effects on them. Mercury (Hg) is one of the main environmental contaminants which globally affect ecosystems and particularly freshwater wildlife. While Hg originates from natural sources, anthropogenic activities such as agriculture, biomass combustion, and gold mining increase its concentrations. Gold mining activities are the main drivers of Hg emission in tropical ecosystems and are responsible for up to 38% of global emissions. Once in its methylated form (MeHg), mercury biomagnifies through the trophic chain and accumulates in top predators. Due to the toxicity of MeHg, long-lived predators are even more subjected to chronic effects as they accumulate Hg over time. In the present study we quantified Hg contamination in two top predators, the Black caiman Melanosuchus niger and the Agami heron Agamia agami, and in their prey in the Kaw-Roura Nature Reserve in French Guiana and evaluated the biomagnification rate in the trophic chain. Our results show that despite a TMF in the range of others in the region (4.38 in our study), top predators of the ecosystem present elevated concentrations of Hg. We have found elevated Hg concentrations in the blood of adult Black caiman (2.10 ± 0.652 µg g-1 dw) and chicks of Agami heron (1.089 ± 0.406 µg g-1 dw). These findings highlight the need to better evaluate the potential impact of Hg in freshwater top predators, especially regarding reprotoxic effects.

Blood Kinetics of Lipophilic and Proteinophilic Pollutants during Two Types of Long-Term Fast in King Penguins.

In vertebrates, fasting is an intricate physiological process associated with strong metabolic changes, yet its effect on pollutant residue variation is poorly understood. Here, we quantified long-term changes in plasma concentrations of 20 organochlorine and 16 perfluoroalkyl pollutants in king penguins Aptenodytes patagonicus during the breeding and molting fasts, which are marked by low and high levels of protein catabolism, respectively, and by strong lipid use. The profile of measured pollutants in plasma was dominated by perfluorooctanesulfonic acid (PFOS, initial relative contribution of 60%). Initial total pollutant concentrations were similar in molting (3.3-5.7 ng g-1 ww) and breeding penguins (range of 4.2-7.3 ng g-1 wet weight, ww). Long-term fasting (25 days) for molting and breeding led, respectively, to a 1.8- and 2.2-fold increase in total plasma pollutant concentrations, although the rate and direction of change were compound-specific. Hexachlorbenzene (HCB) and PFOS concentrations increased in plasma (net mobilization) during both types of fasting, likely due to lipid use. Plasma perfluoroundecanoate (PFUnDA) and perfluorotridecanoate (PFTrDA) concentrations increased in breeders (net mobilization) but decreased in molting individuals (net excretion), suggesting a significant incorporation of these pollutants into feathers. This study is a key contribution to our understanding of pollutant variation in blood during long-term fasting in wildlife.

Living in a challenging environment: Monitoring stress ecology by non-destructive methods in an Antarctic seabird.

How Antarctic species are facing historical and new stressors remains under-surveyed and risks to wildlife are still largely unknown. Adélie penguins Pygoscelis adeliae are well-known bioindicators and sentinels of Antarctic ecosystem changes, a true canary in the coal mine. Immuno-haematological parameters have been proved to detect stress in wild animals, given their rapid physiological response that allows them tracking environmental changes and thus inferring habitat quality. Here, we investigated variation in Erythrocyte Nuclear Abnormalities (ENAs) and White Blood Cells (WBCs) in penguins from three clustered colonies in the Ross Sea, evaluating immuno-haematological parameters according to geography, breeding stage, and individual penguin characteristics such as sex, body condition and nest quality. Concentrations of mercury (Hg) and stable isotopes of carbon and nitrogen (as proxies of the penguin's trophic ecology) were analysed in feathers to investigate the association between stress biomarkers and Hg contamination in Adélie penguins. Colony and breeding stage were not supported as predictors of immuno-haematological parameters. ENAs and WBCs were respectively ∼30 % and ∼20 % higher in male than in female penguins. Body condition influenced WBCs, with penguins in the best condition having a ∼22 % higher level of WBCs than those in the worst condition. Nest position affected the proportion of micronuclei (MNs), with inner-nesting penguins having more than three times the proportion of MNs than penguins nesting in peripheral positions. Heterophils:Lymphocytes (H:L) ratio was not affected by any of the above predictors. Multiple factors acting as stressors are expected to increase prominently in Antarctic wildlife in the near future, therefore extensive monitoring aimed to assess the health status of penguin populations is mandatory.

C and N stable isotopes enlighten the trophic behaviour of the dugong (Dugong dugon).

The dugong (Dugong dugon), a large marine mammal herbivore of the Indo-Pacific, is vulnerable to extinction at a global scale due to a combination of human-related threats including habitat degradation. The species forages on seagrass habitats (marine phanerogams) and plays a key role in the functioning and sensitivity of these declining coastal ecosystems. The trophic behaviour and plasticity of dugong populations in response to extrinsic and intrinsic factors are therefore crucial features to both dugong and seagrass conservation. Yet, this knowledge remains limited to few visual observations and analyses of mouth, stomach or faecal contents of stranded individuals. We take advantage of a long-term monitoring of stranded individuals from the endangered New Caledonian population to depict features of dugongs' trophic ecology from Carbon and Nitrogen stable isotopes. A total of 59 dugong skin samples were used to portrait the stable isotope niche of dugongs according to their sex and maturity. In light of previous work conducted in New Caledonia, a subset of these samples was used to model the trophic mix of dugong males and females. Our stable isotope mixing models used C and N isotope values of 10 taxa bbelonging to five divisions of metazoans, plants, and chromists. Our results represent the first estimate of the species dietary niche in the isotopic space. They suggest that the diet of dugong calves overlaps more with that of adult females (δ13C: - 6.38 ± 1.13 ‰; δ15N: 2.49 ± 1.10 ‰) than males (δ13C: - 5.92 ± 1.10 ‰; δ15N: 3.69 ± 1.28 ‰). Further, we highlight differences in the expected trophic mix of dugong adult males and females. From these, we formulate a sex-specific foraging behaviour hypothesis in dugongs, whereby lactating females could forage over smaller spatial ranges but more diverse food sources thanmales. The study emphasizes the importance of long-term stranding monitoring programs to study the ecology of marine mammals.. Finally, it depicts an ecological feature that may contribute to the sensitivity of vulnerable dugongs to ongoing changes on tropical coastal ecosystems.

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.

Deleterious effects of mercury contamination on immunocompetence, liver function and egg volume in an antarctic seabird.

Mercury (Hg) is a globally important pollutant that can negatively impact metabolic, endocrine and immune systems of marine biota. Seabirds are long-lived marine top predators and hence are at risk of bioaccumulating high Hg concentrations from their prey. Here, we measured blood total mercury (THg) concentrations and relationships with physiology and breeding parameters of breeding brown skuas (Stercorarius antarcticus) (n = 49 individuals) at Esperanza/Hope Bay, Antarctic Peninsula. Mean blood THg concentrations were similar in males and females despite the differences in body size and breeding roles, but differed between study years. Immune markers (hematocrit, Immunoglobulin Y [IgY] and albumin) were negatively correlated with blood THg concentrations, which likely indicates a disruptive effect of Hg on immunity. Alanine aminotransferase (GPT) activity, reflecting liver dysfunction, was positively associated with blood THg. Additionally, triacylglycerol and albumin differed between our study years, but did not correlate with Hg levels, and so were more likely to reflect changes in diet and nutritional status rather than Hg contamination. Egg volume correlated negatively with blood THg concentrations. Our study provides new insights into the sublethal effects of Hg contamination on immunity, liver function and breeding parameters in seabirds. In this Antarctic species, exposure to sublethal Hg concentrations reflects the short-term risks which could make individuals more susceptible to environmental stressors, including ongoing climatic changes.

Assessing mercury contamination in Southern Hemisphere marine ecosystems: The role of penguins as effective bioindicators.

Mercury (Hg) is a global pollutant known for its significant bioaccumulation and biomagnification capabilities, posing a particular threat to marine environments. Seabirds have been recognized as effective bioindicators of marine pollution, and, among them, penguins present a unique opportunity to serve as a single taxonomic group (Sphenisciformes) for monitoring Hg across distinct marine ecosystems in the Southern Hemisphere. In this study, we conducted a comprehensive systematic review of Hg concentrations, and performed a meta-analysis that took into account the various sources of uncertainty associated with Hg contamination in penguins. Beyond intrinsic species-specific factors shaping Hg levels, our results showed that the penguin community effectively reflects spatial patterns of Hg bioavailability. We identified geographic Hg hotspots in Australia, the Indian Ocean, and Tierra del Fuego, as well as coldspots in Perú and the South Atlantic. Furthermore, specific penguin species, namely the Southern Rockhopper (Eudyptes chrysocome) and Macaroni penguin (Eudyptes chrysolophus), are highlighted as particularly vulnerable to the toxic effects of Hg. Additionally, we identified knowledge gaps in geographic areas such as the Galápagos Islands, South Africa, and the coast of Chile, as well as in species including Fiordland (Eudyptes pachyrhynchus), Snares (Eudyptes robustus), Erect-crested (Eudyptes sclateri), Royal (Eudyptes schlegeli), Yellow-eyed (Megadyptes antipodes), and Galápagos (Spheniscus mendiculus) penguins. Overall, our study contributes to the growing body of literature emphasizing the role of penguins as bioindicators of Hg pollution, but it also highlights areas where further research and data collection are needed for a more comprehensive understanding of Hg contamination in marine ecosystems in the Southern Hemisphere.

Poison in the nursery: Mercury contamination in the tadpole-rearing sites of an Amazonian frog.

Artisanal and small-scale gold mining (ASGM) has become a major threat for Neotropical forests. This technique for obtaining gold is a substantial driver of small-scale deforestation and the largest contributor of Hg emissions to both the atmosphere and freshwater systems globally. Previous studies have demonstrated the impacts of Hg accumulation on various aquatic ecosystems and organisms. However, its consequences in other, more discrete systems such as phytotelmata (water-holding plant structures), and the organisms therein, have so far gone unnoticed. Here, we show high concentrations of Hg (mean ± SD: 1.43 ± 2.19 ppm) in phytotelmata and other small pools, the aquatic microenvironments used by the Neotropical poison frog Dendrobates tinctorius as tadpole-rearing sites. In 17 % of the cases, we detected Hg concentrations above the severe effect level (SEL = 2 ppm) for freshwater sediments. Hg concentrations varied depending on pool characteristics and tended to increase in proximity to known ASGM sites. We did not find an effect of Hg concentration on the number of D. tinctorius tadpoles in a given pool. Tadpoles were found in pools with concentrations of up to 8.68 ppm, suggesting that D. tinctorius fathers do not avoid pools with high Hg levels for tadpole deposition. While further research is needed to determine the potential effects of Hg on tadpole development, we found an intriguing tendency for tadpoles in later developmental stages to have lower body condition when occurring in pools with higher Hg concentrations. Our findings provide evidence of relevant Hg concentrations in the terrestrial water systems used by phytotelm-breeding anurans, and highlight the need of further field and experimental studies investigating the implications of Hg contamination for tadpole development and behaviour and the overall conservation of Amazonian biodiversity.

Is bedding material a more effective thermal insulator than trap cover for small mammal trapping? A field experiment.

Live trapping is a key technique for conducting ecological studies on small mammals. All-metal live traps are popular in monitoring schemes owing to their tested performance, lightweight design (aluminium) and foldability. However, capture represents a stressful situation for small mammals, particularly during cold seasons, when individuals are susceptible to cold weather starvation resulting from low temperature and insufficient food to maintain body temperature. Metal live traps provide limited protection against cold temperatures, and it is often recommended to use covers to buffer external temperature fluctuations and prevent entry of moisture. Here, we compared the insulative performance of a PVC cover designed for Sherman traps and of bedding material, using data loggers to record temperature and humidity inside traps. We conducted different experiments simulating field conditions (traps at night with a heat source inside) and different treatments (cover, bedding material) to test the thermal insulation capacity of three models of widely used commercial traps: Longworth, Sherman, and Heslinga. Our findings indicated that Longworth and Sherman traps were better insulated against ambient air temperature fluctuations than Heslinga traps (+2.0 °C warmer on average). Bedding material was paramount in reducing relative humidity and increasing thermal insulation capacity of traps (+3.1 °C), an effect that was strengthened when a PVC cover was additionally used (+4.2 °C). The covered traps prevented the direct entrance of rain and dew (reducing damp bedding), provided camouflage (reducing thefts), and improved thermal and humidity conditions of traps (potentially increasing survival of captive small mammals). Our results suggest that using covers and bedding materials can improve thermal and humidity conditions within live traps, thus reducing the metabolic costs of thermoregulation and increasing survival chances for trapped small mammals during cold seasons.

High urinary oxidative DNA damage in wild chimpanzees ranging in proximity of agricultural fields in Sebitoli area, Uganda.

Agriculture expansion is a major cause of habitat loss and exposure to phytochemical pollution for non-human primates. In addition to endocrine disruption, exposure to pesticides may have other sublethal physiological consequences for animals, such as generation of oxidative damage to macromolecules. In this study, we analyzed the pesticides contained in the river water across the home range of wild chimpanzees (Pan troglodytes) in Sebitoli area located on the Northern part of Kibale National Park (Uganda). We tested whether levels of three urinary markers of oxidative damage vary among individuals in relation to their ranging patterns, as a proxy for pesticide exposure intensity. To better characterize the foraging habitat use, the trophic level, and the energetic status of study individuals, we also quantified urinary levels of carbon and nitrogen stable isotope signatures and of C-peptide. Among the 511 pesticides screened, 18 compounds including herbicides, insecticides, and fungicides were found in the water sampled in the Western part of the home range of chimpanzees. In this area, chimpanzees used to feed on maize crops. By contrast, in the Eastern part where crop feeding was never observed, we found only seven pesticides. According to their ranging patterns and thus crop feeding frequency, the 139 urine samples collected from 43 Sebitoli chimpanzees were categorized as belonging to low, medium, and high exposure level. Chimpanzees from the high exposure zone had higher oxidative DNA damage (8-OHdG) than chimpanzees from both the low and medium exposure groups, who had similar levels of oxidative DNA damage. In addition, individuals with higher C-peptide tended to have significantly higher oxidative DNA damage and lipid peroxides. The three exposure groups had similar levels of urinary 8-isoprostanes and of urinary lipid peroxides. These results were robust for any potential confounding effect of other variables because neither age category nor sex or isotope levels were significantly associated with markers of oxidative damage. Our study points to genotoxic effects as one potential sublethal consequence of ranging in proximity of agricultural fields owing to exposure to pesticides or other unidentified sources of stress. Given our phylogenetic proximity, this information is relevant for the conservation of this species which is endangered and also sentinel for human health.

Circumpolar assessment of mercury contamination: the Adélie penguin as a bioindicator of Antarctic marine ecosystems.

Due to its persistence and potential ecological and health impacts, mercury (Hg) is a global pollutant of major concern that may reach high concentrations even in remote polar oceans. In contrast to the Arctic Ocean, studies documenting Hg contamination in the Southern Ocean are spatially restricted and large-scale monitoring is needed. Here, we present the first circumpolar assessment of Hg contamination in Antarctic marine ecosystems. Specifically, the Adélie penguin (Pygoscelis adeliae) was used as a bioindicator species, to examine regional variation across 24 colonies distributed across the entire Antarctic continent. Mercury was measured on body feathers collected from both adults (n = 485) and chicks (n = 48) between 2005 and 2021. Because penguins' diet represents the dominant source of Hg, feather δ13C and δ15N values were measured as proxies of feeding habitat and trophic position. As expected, chicks had lower Hg concentrations (mean ± SD: 0.22 ± 0.08 µg·g‒1) than adults (0.49 ± 0.23 µg·g‒1), likely because of their shorter bioaccumulation period. In adults, spatial variation in feather Hg concentrations was driven by both trophic ecology and colony location. The highest Hg concentrations were observed in the Ross Sea, possibly because of a higher consumption of fish in the diet compared to other sites (krill-dominated diet). Such large-scale assessments are critical to assess the effectiveness of the Minamata Convention on Mercury. Owing to their circumpolar distribution and their ecological role in Antarctic marine ecosystems, Adélie penguins could be valuable bioindicators for tracking spatial and temporal trends of Hg across Antarctic waters in the future.

Mercury contamination in the tropical seabird community from Clipperton Island, eastern Pacific Ocean.

Mercury (Hg) pollution is a global problem affecting remote areas of the open ocean, but the bioaccumulation of this neurotoxic pollutant in tropical top predators remains poorly documented. The objective of this study was to determine Hg contamination of the seabird community nesting on Clipperton Island using blood and feathers to investigate short and longer-term contamination, respectively. We examined the significance of various factors (species, sex, feeding habitat [δ13C] and trophic position [δ15N]) on Hg concentrations in six seabird species. Among species, Great Frigatebirds had the highest Hg concentrations in blood and feathers, boobies had intermediate values, and Brown Noddies and Sooty Terns the lowest. At the interspecific level, although δ13C values segregated boobies from frigatebirds and noddies/terns, Hg concentrations were explained by neither δ13C nor δ15N values. At the intraspecific level, both Hg concentrations in blood and feathers show relatively small variations (16-32 and 26-74%, respectively), suggesting that feeding ecology had low seasonal variation among individuals. Despite most species being sexually dimorphic, differences in Hg contamination according to sex was detected only in Brown Boobies during the breeding period. Indeed, female Brown Boobies feed at a higher trophic level and in a different area than males during this period, resulting in higher blood Hg concentrations. The present study also shows that most of the seabirds sampled at Clipperton Island had little or no exposure to Hg toxicity, with 30% in the no risk category and 70% in the low risk category.

Variation of 210-polonium in the cephalopod community from the Bay of Biscay, North-East Atlantic.

Among natural radionuclides, 210Po is the major contributor to the radiation dose received by marine organisms. In cephalopods, 210Po is concentrated in the digestive gland, which contains over 90% of the whole-body burden of the nuclide. Although previous studies showed that 210Po was taken up independently of 210Pb, its parent nuclide, very little is known about the factors influencing its levels in cephalopods. To the best of our knowledge, no studies investigated 210Po levels in different species at the same time. In the present study, 210Po was analysed in the digestive gland of 62 individuals from 11 species representing a large range of feeding ecologies and habitats, including squids, cuttlefish and octopus species from coastal to deep-oceanic habitats. Among species, the highest activity was measured in Loligo vulgaris (5720 ± 3606 Bq/kg) and the lowest in T. megalops (188 Bq/kg). However, considering the habitats (benthic vs pelagic and neritic vs oceanic), no significant differences appeared. At the species level, no differences between sexes were found so both sexes were plotted together to test the size effect for species with at least 8 individuals (i.e., Eledone cirrhosa, L. vulgaris, L. forbesi and Sepia officinalis). In the first three species, 210Po levels decreased significantly with increasing size or weight but not in S. officinalis. In squid, this could be related to ontogenetic changes in diet from a high proportion of crustaceans (high Po content) in small individuals to fish (low Po content) in larger individuals, while the high dietary plasticity of S. officinalis at all stages of its life cycle could explain the lack of decrease in 210Po with size. In comparison to the few data from the literature, the levels of 210Po concentrations in the cephalopod community of the Bay of Biscay were overall in the same range than those reported in other cephalopods, varying across 4 orders of magnitude. Further studies are needed to understand the mechanism of retention in the cephalopod digestive gland.

Development of an integrated indicator to assess chemical contamination in different marine species: The case of mercury on the French Atlantic continental shelf.

Good Environmental Status (GES) for Descriptor 8 (D8) of the Marine Strategy Framework Directive (MSFD) is considered to be achieved when concentrations of contaminants are at levels not giving rise to pollution effects. This study proposes a framework to assess GES in marine waters adjacent to France, including four groups of species (bivalves, fish, birds and mammals) living on the continental shelf and covering different dimensions of the marine environment. This framework is applied to mercury (Hg) in the three marine regions along the French Atlantic coast and includes two assessment types: i) an absolute assessment by comparing contamination levels with environmental thresholds, and ii) a relative assessment by comparing contamination levels over time, performed for bivalves and mammals that had long time-series available. Mercury concentrations were higher than environmental thresholds for bivalves and fish in all the three studied regions. Plus, they significantly increased since the 2000s for most bivalve stations and for the common dolphin Delphinus delphis. Our results therefore indicate that Hg concentrations have increased in marine waters and have reached levels possibly giving rise to pollution effects in biota from the three marine regions. The present study also highlighted the complementarity of monitoring Hg concentrations in each group of species and each type of assessment, making it possible to propose a conceptual framework for assessing the environmental pressure of bioaccumulated and biomagnified contaminants over the continental shelf.

Mercury in Ten Storm-Petrel Populations from the Antarctic to the Subtropics.

The oceans become increasingly contaminated as a result of global industrial production and consumer behaviour, and this affects wildlife in areas far removed from sources of pollution. Migratory seabirds such as storm-petrels may forage in areas with different contaminant levels throughout the annual cycle and may show a carry-over of mercury from the winter quarters to the breeding sites. In this study, we compared mercury levels among seven species of storm-petrels breeding on the Antarctic South Shetlands and subantarctic Kerguelen Islands, in temperate waters of the Chatham Islands, New Zealand, and in temperate waters of the Pacific off Mexico. We tested for differences in the level of contamination associated with breeding and inter-breeding distribution and trophic position. We collected inert body feathers and metabolically active blood samples in ten colonies, reflecting long-term (feathers) and short-term (blood) exposures during different periods ranging from early non-breeding (moult) to late breeding. Feathers represent mercury accumulated over the annual cycle between two successive moults. Mercury concentrations in feathers ranged over more than an order of magnitude among species, being lowest in subantarctic Grey-backed Storm-petrels (0.5 µg g-1 dw) and highest in subtropical Leach's Storm-petrels (7.6 µg g-1 dw, i.e. posing a moderate toxicological risk). Among Antarctic Storm-petrels, Black-bellied Storm-petrels had threefold higher values than Wilson's Storm-petrels, and in both species, birds from the South Shetlands (Antarctica) had threefold higher values than birds from Kerguelen (subantarctic Indian Ocean). Blood represents mercury taken up over several weeks, and showed similar trends, being lowest in Grey-backed Storm-petrels from Kerguelen (0.5 µg g-1 dw) and highest in Leach's Storm-petrels (3.6 µg g-1 dw). Among Antarctic storm-petrels, species differences in the blood samples were similar to those in feathers, but site differences were less consistent. Over the breeding season, mercury decreased in blood samples of Antarctic Wilson's Storm-petrels, but did not change in Wilson's Storm-petrels from Kerguelen or in Antarctic Black-bellied Storm-petrels. In summary, we found that mercury concentrations in storm-petrels varied due to the distribution of species and differences in prey choice. Depending on prey choices, Antarctic storm-petrels can have similar mercury concentrations as temperate species. The lowest contamination was observed in subantarctic species and populations. The study shows how seabirds, which accumulate dietary pollutants in their tissues in the breeding and non-breeding seasons, can be used to survey marine pollution. Storm-petrels with their wide distributions and relatively low trophic levels may be especially useful, but more detailed knowledge on their prey choice and distributions is needed.

A keystone avian predator faces elevated energy expenditure in a warming Arctic.

Climate change is transforming bioenergetic landscapes, challenging behavioral and physiological coping mechanisms. A critical question involves whether animals can adjust behavioral patterns and energy expenditure to stabilize fitness given reconfiguration of resource bases, or whether limits to plasticity ultimately compromise energy balance. In the Arctic, rapidly warming temperatures are transforming food webs, making Arctic organisms strong models for understanding biological implications of climate change-related environmental variability. We examined plasticity in the daily energy expenditure (DEE) of an Arctic seabird, the little auk (Alle alle) in response to variability in climate change-sensitive drivers of resource availability, sea surface temperature (SST) and sea ice coverage (SIC), and tested the hypothesis that energetic ceilings and exposure to mercury, an important neurotoxin and endocrine disrupter in marine ecosystems, may limit scope for plasticity. To estimate DEE, we used accelerometer data obtained across years from two colonies exposed to distinct environmental conditions (Ukaleqarteq [UK], East Greenland; Hornsund [HS], Svalbard). We proceeded to model future changes in SST to predict energetic impacts. At UK, high flight costs linked to low SIC and high SST drove DEE from below to above 4 × basal metabolic rate (BMR), a proposed energetic threshold for breeding birds. However, DEE remained below 7 × BMR, an alternative threshold, and did not plateau. Birds at HS experienced higher, relatively invariable SST, and operated above 4 × BMR. Mercury exposure was unrelated to DEE, and fitness remained stable. Thus, plasticity in DEE currently buffers fitness, providing resiliency against climate change. Nevertheless, modeling suggests that continued warming of SST may promote accelerating increases in DEE, which may become unsustainable.

Do foraging ecology and contaminants interactively predict parenting hormone levels in common eider?

Global climate change is causing abiotic shifts such as higher air and ocean temperatures, and disappearing sea ice in Arctic ecosystems. These changes influence Arctic-breeding seabird foraging ecology by altering prey availability and selection, affecting individual body condition, reproductive success, and exposure to contaminants such as mercury (Hg). The cumulative effects of alterations to foraging ecology and Hg exposure may interactively alter the secretion of key reproductive hormones such as prolactin (PRL), important for parental attachment to eggs and offspring and overall reproductive success. However, more research is needed to investigate the relationships between these potential links. Using data collected from 106 incubating female common eiders (Somateria mollissima) at six Arctic and sub-Arctic colonies, we examined whether the relationship between individual foraging ecology (assessed using δ13C, δ15N) and total Hg (THg) exposure predicted PRL levels. We found a significant, complex interaction between δ13C, δ15N and THg on PRL, suggesting that individuals cumulatively foraging at lower trophic levels, in phytoplankton-dominant environments, and with the highest THg levels had the most constant significant relationship PRL levels. Cumulatively, these three interactive variables resulted in lowered PRL. Overall, results demonstrate the potential downstream and cumulative implications of environmentally induced changes in foraging ecology, in combination with THg exposure, on hormones known to influence reproductive success in seabirds. These findings are notable in the context of continuing environmental and food web changes in Arctic systems, which may make seabird populations more susceptible to ongoing stressors.

In Vivo Mercury (De)Methylation Metabolism in Cephalopods under Different pCO2 Scenarios.

This work quantified the accumulation efficiencies of Hg in cuttlefish, depending on both organic (MeHg) and inorganic (Hg(II)) forms, under increased pCO2 (1600 µatm). Cuttlefish were fed with live shrimps injected with two Hg stable isotopic tracers (Me202Hg and 199Hg(II)), which allowed for the simultaneous quantification of internal Hg accumulation, Hg(II) methylation, and MeHg demethylation rates in different organs. Results showed that pCO2 had no impact on Hg bioaccumulation and organotropism, and both Hg and pCO2 did not influence the microbiota diversity of gut and digestive gland. However, the results also demonstrated that the digestive gland is a key organ for in vivo MeHg demethylation. Consequently, cuttlefish exposed to environmental levels of MeHg could exhibit in vivo MeHg demethylation. We hypothesize that in vivo MeHg demethylation could be due to biologically induced reactions or to abiotic reactions. This has important implications as to how some marine organisms may respond to future ocean change and global mercury contamination.

Cuttlefish color change as an emerging proxy for ecotoxicology.

Lately, behavioral ecotoxicology has flourished because of increasing standardization of analyses of endpoints like movement. However, research tends to focus on a few model species, which limits possibilities of extrapolating and predicting toxicological effects and adverse outcomes at the population and ecosystem level. In this regard, it is recommended to assess critical species-specific behavioral responses in taxa playing key roles in trophic food webs, such as cephalopods. These latter, known as masters of camouflage, display rapid physiological color changes to conceal themselves and adapt to their surrounding environments. The efficiency of this process depends on visual abilities and acuity, information processing, and control of chromatophores dynamics through nervous and hormonal regulation with which many contaminants can interfere. Therefore, the quantitative measurement of color change in cephalopod species could be developed as a powerful endpoint for toxicological risk assessment. Based on a wide body of research having assessed the effect of various environmental stressors (pharmaceutical residues, metals, carbon dioxide, anti-fouling agents) on the camouflage abilities of juvenile common cuttlefish, we discuss the relevance of this species as a toxicological model and address the challenge of color change quantification and standardization through a comparative review of the available measurement techniques.

A century of mercury: Ecosystem-wide changes drive increasing contamination of a tropical seabird species in the South Atlantic Ocean.

Mercury (Hg) is a highly toxic metal that adversely impacts human and wildlife health. The amount of Hg released globally in the environment has increased steadily since the Industrial Revolution, resulting in growing contamination in biota. Seabirds have been extensively studied to monitor Hg contamination in the world's oceans. Multidecadal increases in seabird Hg contamination have been documented in polar, temperate and subtropical regions, whereas in tropical regions they are largely unknown. Since seabirds accumulate Hg mainly from their diet, their trophic ecology is fundamental in understanding their Hg exposure over time. Here, we used the sooty tern (Onychoprion fuscatus), the most abundant tropical seabird, as bioindicator of temporal variations in Hg transfer to marine predators in tropical ecosystems, in response to trophic changes and other potential drivers. Body feathers were sampled from 220 sooty terns, from museum specimens (n = 134) and free-living birds (n = 86) from Ascension Island, in the South Atlantic Ocean, over 145 years (1876-2021). Chemical analyses included (i) total- and methyl-Hg, and (ii) carbon (δ1³C) and nitrogen (δ15N) stable isotopes, as proxies of foraging habitat and trophic position, respectively, to investigate the relationship between trophic ecology and Hg contamination over time. Despite current regulations on its global emissions, mean Hg concentrations were 58.9% higher in the 2020s (2.0 µg g-1, n = 34) than in the 1920s (1.2 µg g-1, n = 107). Feather Hg concentrations were negatively and positively associated with δ1³C and δ15N values, respectively. The sharp decline of 2.9 ‰ in δ1³C values over time indicates ecosystem-wide changes (shifting primary productivity) in the tropical South Atlantic Ocean and can help explain the observed increase in terns' feather Hg concentrations. Overall, this study provides invaluable information on how ecosystem-wide changes can increase Hg contamination of tropical marine predators and reinforces the need for long-term regulations of harmful contaminants at the global scale.