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Understanding variations in metal levels in biota geographically and under different environmental conditions is essential to determining risk to organisms themselves and to their predators. It is often difficult to determine food chain relationships because predators may eat several different prey types. Horseshoe crab (Limulus polyphemus) eggs form the basis for a complex food web in Delaware Bay, New Jersey, USA. Female horseshoe crabs lay thumb-sized clutches of eggs, several cm below the surface, and often dislodge previously laid eggs that are brought to the surface by wave action, where they are accessible and critical food for migrant shorebirds. This paper compares metal and metalloid (chromium [Cr], cadmium [Cd], lead [Pb], mercury [Hg], arsenic [As] and selenium [Se]) concentrations in horseshoe crab eggs collected on the surface with concentrations in eggs from clutches excavated from below the sand surface, as well as examining metals in eggs from different parts of the Bay. The eggs were all collected in May 2019, corresponding to the presence of the four main species of shorebirds migrating through Delaware Bay. These migrating birds eat almost entirely horseshoe crab eggs during their stopover in Delaware Bay, and there are differences in the levels of metals in blood of different shorebirds. These differences could be due to whether they have access to egg clutches below sand (ruddy turnstones, Arenaria interpres) or only to eggs on the surface (the threatened red knot [Calidris canutus rufa] and other species of shorebirds). Correlations between metals in clutches were also examined. Except for As and Cd, there were no significant differences between the metals in crab egg clutches and eggs on the surface that shorebirds, gulls, and other predators eat. There were significant locational differences in metal levels in horseshoe crab eggs (except for Pb), with most metals being highest in the sites on the lower portion of Delaware Bay. Most metals in crab eggs have declined since studies were conducted in the mid-1990s but were similar to levels in horseshoe crab eggs in 2012. The data continue to provide important monitoring and assessment information for a keystone species in an ecosystem that supports many species, including threatened and declining shorebird species during spring migration.

Socially synchronized rhythms in shorebirds were assessed during biparental incubation under natural circumstances and were exceptionally diverse, often not following the 24-h day, whereby risk of predation, not starvation, determined some of the variation in incubation rhythms. Sharing the burden of parental care All organisms have biorhythms, but in social species these have to be synchronized between individuals within a community. Here Martin Bulla et al . address the issue of how parents synchronize their biorhythms when both are caring for their offspring. Using data from 729 nests of 91 populations of 32 species of shorebirds in which parents synchronize their schedules to achieve continuous incubation of the eggs, they show that even under similar environmental conditions and despite day-long environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of captive birds. The risk of predation, not starvation, might be a key determinant of biorhythmic diversity. The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment 1 , 2 , 3 , 4 . Such behavioural rhythms are well studied in isolated individuals under laboratory conditions 1 , 5 , but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators 6 , 7 , 8 , 9 , 10 . Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring) 6 , 7 , 8 , 9 , 11 . The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood 5 , 6 , 7 , 9 . Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization 12 where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within- and between-species diversity in incubation rhythms. Between species, the median length of one parent’s incubation bout varied from 1–19 h, whereas period length—the time in which a parent’s probability to incubate cycles once between its highest and lowest value—varied from 6–43 h. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or who actively protect their nest against predators. Rhythms entrainable to the 24-h light–dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity 5 , 6 , 7 , 9 . The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.

Eating fish is often recommended as part of a healthful diet. However, fish, particularly large predatory fish, can contain significant levels of the highly toxic methylmercury (MeHg). Ocean fish in general also contain high levels of selenium (Se), which is reported to confer protection against toxicity of various metals including mercury (Hg). Se and Hg have a high mutual binding affinity, and each can reduce the toxicity of the other. This is an evolving area of extensive research and controversy with variable results in the animal and epidemiologic literature. MeHg is toxic to many organ systems through high affinity for –SH (thiol) ligands on enzymes and microtubules. Hg toxicity also causes oxidative damage particularly to neurons in the brain. Hg is a potent and apparently irreversible inhibitor of the selenoenzymes, glutathione peroxidases (GPX), and thioredoxin reductases (TXNRD) that are important antioxidants, each with a selenocysteine (SeCys) at the active site. Hg binding to the SeCys inhibits these enzymes, accounting in part for the oxidative damage that is an important manifestation of Hg toxicity, particularly if there is not a pool of excess Se to synthesize new enzymes. A molar excess of Se reflected in an Se:Hg molar ratio > 1 is often invoked as evidence that the Hg content can be discounted. Some recent papers now suggest that if the Se:Hg molar ratio exceeds 1:1, the fish is safe and the mercury concentration can be ignored. Such papers suggested that the molar ratio rather than the Hg concentration should be emphasized in fish advisories. This paper examines some of the limitations of current understanding of the Se:Hg molar ratio in guiding fish consumption advice; Se is certainly an important part of the Hg toxicity story, but it is not the whole story. We examine how Hg toxicity relates also to thiol binding. We suggest that a 1:1 molar ratio cannot be relied on because not all of the Se in fish or in the fish eater is available to interact with Hg. Moreover, in some fish, Se levels are sufficiently high to warrant concern about Se toxicity.

To conserve threatened/endangered species, we need to understand the factors contributing to reproductive success and recruitment to reproductive stage. Obtaining this information is difficult for snakes because they are secretive, are not easy to locate at the same stage each year, and are sometimes sparsely distributed. We determined nest fate, hatchling growth and survival to age 5 years, and recruitment to breeding age of Northern Pine Snakes (Pituophis melanoleucus) in New Jersey Pine Barrens from 1986 to 2017. Pine Snakes are 'threatened' in New Jersey and in other states, and are at risk because of increased human population, habitat loss, predation, and poaching. Age of first-breeding was 4-years, based on snout-vent length of gravid and laying females, and snout-vent length of females followed as hatchlings to 5-years. Mean clutch size (+ 1 SE) was 9.5 + 0.3 (N = 53). The annual percent of nests in which eggs hatched averaged 25% (N = 288 nests), and varied among 5-year periods (5% to 30%/year). Of lab-reared hatchlings released into natal nests (N = 90), 26% (2015) and 32% (2016) reached hibernacula excavated in 2016 and 2017. The sex ratio of hatchlings reaching hibernation sites (N = 181) between 1986 and 2015 was skewed toward females (74/106, 59% females), and varied among 5-year periods (47-75% females). Once hatchlings reached a hibernaculum, there was a sex-related difference in survival. For hatchlings reaching a monitored hibernaculum, survival to 3-years was 35% in females and 40% in males, and to 4-years was 25% in females and 33% in males. Using these data, only 10% of females reached 3 years (first possible breeding age), and 7% survived to 4-years. Methodological problems with determining survival rates during these early critical years are discussed.

The elements in blood normally reflect the levels in prey, indicating a recent exposure. Laughing gulls (Leucophaes atricilla) eat mainly horseshoe crab eggs (Limulus polyphemus) in the spring in Delaware Bay, New Jersey. The levels of arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and selenium (Se) in the blood of laughing gulls foraging on crab eggs were examined in Delaware Bay to provide information on a species that is normally a generalist, and to determine if the levels of these elements were similar in 2019 and 2022/2023, were intercorrelated, and were related to those in crab eggs. Hg increased from 2019 (136 ± 31 ng/g) to 2022/2023 (473 ± 75 ng/g), while Cd and Se decreased. There were some significant correlations among elements and a close relationship between the element levels in blood and those in crab eggs collected in the same month (except for As). The levels differed between laughing gulls and three species of shorebirds for As and Cd. The elements in the blood of gulls and shorebirds should be similar because they eat mainly the same eggs in the same places. A significant proportion of laughing gull blood samples had levels of Hg and Se that were above the levels associated with adverse effects, which requires further examination.

Examining contaminant concentrations in birds in Arctic environments is important for managing species for assessing long-term trends. Recent reports on mercury (Hg) concentrations in Arctic species of seabirds has identified a need for data from missing regions or species. We measured arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), manganese (Mn), Hg and selenium (Se) in the body feathers of Atlantic Puffin (Fratercula arctica) from four colonies in Iceland in 2011 and one in 2009. Puffins forage on small fish at an intermediate trophic concentration. We found that (1) concentrations examined in the colony in 2009 were lower than in 2011 for all metals except As and Hg, and (2) concentrations of Cd and Se varied significantly among colonies for feathers collected in 2011. Pb concentrations in Puffin feathers in one colony were 14-fold higher in 2009 than in 2011 (mean of 805 ng.g−1 vs. 58 ng.g−1). The highest mean Hg concentration in 2011 was 362 ng.g−1 and was 4880 ng.g−1 for Se. The concentrations of Hg in the Atlantic Puffins reported in this study were similar to, or lower than those reported for the same species elsewhere and for Tufted Puffin from the Pacific.

Many shorebird populations are declining, and contaminants may be partly contributing to the decline by interfering with feeding, migration, and breeding success. The goal of our study was to determine whether there was a temporal change in concentrations of trace elements of red knot ( Calidris canutus rufa ), sanderling ( Calidris alba ), and ruddy turnstone ( Arenaria interpres ) during spring migration in Delaware Bay, New Jersey, USA. We sampled blood to 1) determine levels of trace elements in 2019, 2) compare 2019 trace element levels with those from shorebirds in 2011–2012, and 3) examine variability in blood levels of trace elements among species. In 2019: 1) trace element levels were significantly different among species (except cadmium[Cd]), 2) Cd was lowest in all species, and arsenic (As) and selenium (Se) were highest, and 3) sanderlings had the highest levels of As and Se, and knots had the highest levels of chromium (Cr) and lead (Pb). Se was higher in these shorebirds than reported for other shorebirds from elsewhere. As, mercury (Hg), and Se increased significantly between 2011–2012 and 2019 in all three species. There were no significant temporal changes in Cd. Chromium (Cr) decreased in knots and sanderling. The temporal increases in As, Se, and Hg bear watching as they are toxic in vertebrates, and each can decrease the toxicity of the others. The data indicate that shorebirds can be bioindicators of changing trace element levels in estuaries, potentially providing early warning of increasing levels of As, Hg, and Se in the environment.

Ophidiomyces ophidiicola, the fungus causing Snake Fungal Disease (SFD) or ophidiomycosis, is prevalent in North American snakes and can have deleterious population effects. Northern pine snakes (Pituophis melanoleucus melanoleucus) in New Jersey often test positive for ophidiomycosis. In this paper, we use qPCR to examine changes in prevalence from 2018 to 2023, and differences by age, sex, and morphological sampling locations. We swabbed ventral surfaces, head, and cloaca of snakes, and lesions and eyes if there were clinical ophidiomycosis signs. A snake was considered positive if any site was positive by qPCR. The prevalence was 47% (2018), increased to 100% (2022), but declined to 46% in 2023. The prevalence was highest in snakes with lesions (46–100%); head swabs had the lowest rates. The more lesions a snake had, the more likely it was that at least one would be positive. Males had significantly more lesions than females, but the prevalence was similar. In 2023, the prevalence of O. ophidiicola was low, but the prevalence of lesions did not decrease as markedly. We discuss the temporal changes in the positivity for O. ophidiicola and its implications for ophidiomycosis effects, suggesting that the fungus is endemic in this population.

The mutual mitigation of selenium and mercury toxicity is particularly interesting, especially for humans. Mercury is widely recognized as a pantoxic element; all forms are toxic to all organisms. Less well known is that selenium in excess is toxic as well. The high affinity between these elements influences their bioavailability and toxicity. In this paper, we use selected species from Barnegat and Delaware Bays in New Jersey to examine variations in levels of selenium and mercury, and selenium:mercury molar ratios between and within species. We report on species ranging from horseshoe crab eggs ( Limulus polyphemus ), a keystone species of the food chain, to several fish species, to fish-eating birds. Sampling began in the 1970s for some species and in the 1990s for others. We found no clear time trends in mercury levels in horseshoe crab eggs, but selenium levels declined at first, then remained steady after the mid1990s. Concentrations of mercury and selenium in blood of migrant shorebirds directly reflected levels in horseshoe crab eggs (their food at stopover). Levels of mercury in eggs of common terns ( Sterna hirundo ) varied over time, and may have declined slightly since the mid2000s; selenium levels also varied temporally, and declined somewhat. There were variations in mercury and selenium levels in commercial, recreational, and subsistence fish as a function of species, season, and size (a surrogate for age). Selenium:mercury molar ratios also varied as a function of species, year, season, and size in fish. While mercury levels increased with size within individual fish species, selenium levels remained the same or declined. Thus selenium:mercury molar ratios declined with size in fish, reducing the potential of selenium to ameliorate mercury toxicity in consumers. Mercury levels in fish examined were higher in early summer and late fall, and lower in the summer, while selenium stayed relatively similar; thus selenium:mercury molar ratios were lower in early summer and late fall than in midsummer. We discuss the importance of temporal trends in biomonitoring projects, variations in levels of mercury, selenium, and the molar ratios as a function of several variables, and the influence of these on risks to predators and humans eating the fish, and the eggs of gulls, terns. Our data suggests that variability limits the utility of the selenium:mercury molar ratio for fish consumption advisories and for risk management.

We examined traditional environmental justice populations and other groups whose exposure to contaminants is often disproportionately high. Risk assessment methods may not identify these populations, particularly if they are spatially dispersed. We suggest using a National Health and Nutrition Examination Survey approach to oversample minority communities and develop methods for assessing exposure at different distances from pollution sources; publishing arithmetic and geometric means and full distributions for minority populations; and paying particular attention to high-end exposures. Means may sufficiently characterize populations as a whole but are inadequate in identifying vulnerable groups and subgroups. The number of individuals above the 95th percentile of any distribution may be small and unrepresentative, but these outliers are the ones who need to be protected.