Forest management can alter the mobilization of mercury (Hg) into headwater streams and its conversion to methylmercury (MeHg), the form that bioaccumulates in aquatic biota and biomagnifies through food webs. As headwater streams are important sources of organic materials and nutrients to larger systems, this connectivity may also increase MeHg in downstream biota through direct or indirect effects of forestry on water quality or food web structure. In this study, we collected water, seston, food sources (biofilm, leaves, organic matter), five macroinvertebrate taxa and fish (slimy sculpin; Cottus cognata) at 6 sites representing different stream orders (1–5) within three river basins with different total disturbances from forestry (both harvesting and silviculture). Methylmercury levels were highest in water and some food sources from the basin with moderate disturbance (greater clearcutting but less silviculture). Water, leaves, stoneflies and fish increased in MeHg or total Hg along the river continuum in the least disturbed basin, and there were some dissipative effects of forest management on these spatial patterns. Trophic level (δ¹⁵N) was a significant predictor of MeHg (and total Hg in fish) within food webs across all 18 sites, and biomagnification slopes were significantly lower in the basin with moderate total disturbance but not different in the other two basins. The elevated MeHg in lower trophic levels but its reduced trophic transfer in the basin with moderate disturbance was likely due to greater inputs of sediments and of dissolved organic carbon that is more humic, as these factors are known to both increase transport of Hg to streams and its uptake in primary producers but to also decrease MeHg bioaccumulation in consumers. Overall, these results suggest that the type of disturbance from forestry affects MeHg bioaccumulation and trophic transfer in stream food webs and some longitudinal patterns along a river continuum.

Estuaries provide critical habitat for food webs supporting fish and shellfish consumed by humans, but estuarine ecosystem health has been threatened by increases in nitrogen loading as well as inputs of the neurotoxin, mercury (Hg), which biomagnifies in food webs and poses risk to humans and wildlife. In this study, the effects of nutrient loading on the fate of Hg in shallow coastal estuaries were examined to evaluate if their interaction enhances or reduces Hg bioavailability in sediments, the water column, and concentrations in lower trophic level fish (Fundulus heteroclitus and Menidia menidia). Multiple sites were sampled within two human impacted coastal lagoons, Great South Bay (GSB) and Jamaica Bay (JB), on the southern coast of Long Island, NY, United States of America (U.S.A.). Carbon (C), nitrogen (N), sulfur (S), Hg, and methylmercury (MeHg) were measured in surface sediments and the water column, and total Hg (THg) was measured in two species of forage fish. Minimal differences were found in dissolved and particulate Hg, dissolved organic carbon (DOC), and salinity between the two bays. Across lagoons, concentrations of chlorophyll-a were correlated with total suspended solids (TSS), and water column THg and MeHg was largely associated with the particulate fraction. Methylmercury concentrations in particulates decreased with increasing TSS and chlorophyll-a, evidence of biomass dilution of MeHg with increasing productivity at the base of the food chain. Water column Hg was associated with THg concentrations in Atlantic silversides, while mummichog THg concentrations were related to sediment concentrations, reflecting their different feeding strategies. Finally, higher nutrient loading (lower C:N in sediments) while related to lower particulate concentrations coincided with higher bioaccumulation factors (BAF) for Hg in both fish species. Thus, in shallow coastal lagoons, increased nutrient loading resulted in decreased Hg concentrations at the base of the food web but resulted in greater bioaccumulation of Hg to fish relative to its availability in algal food.

Seabird eggs are considered a favourable matrix for monitoring marine pollutants and are widely used as higher trophic level indicators. Persistent organic pollutants such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and other organochlorine compounds (OCs) as well as metals have been shown to have deleterious impacts on seabirds. The Northern Gannet Morus bassanus is an avian sentinel; the largest breeding seabird in Ireland and an obligate piscivore. Gannet eggs were collected from two island colonies off the east coast of Ireland in locations with divergent history of industrialisation. Contaminant levels were measured and differences in concentrations between colonies compared. Stable isotope ratios of carbon (δ₁₃C) and nitrogen (δ₁₅N) were measured in each egg to understand the influence of diet and trophic position on contaminant levels detected. Significantly higher levels of Σ14PCBs, Σ7PBDEs and total mercury were detected in Gannet eggs from Lambay Island near Dublin (Ireland’s industrialised capital city) compared to Great Saltee Island. No differences were observed in levels of other OCs (HCB, ΣHCH, ΣCHL, ΣDDT) between the two colonies. Though Gannets travel significant distances when foraging for food, tracking studies have demonstrated that birds from proximal breeding colonies maintain exclusive feeding areas. Stable isotope ratio analysis in this study demonstrated that Gannets at both locations occupy similar dietary niches, indicating that dietary differences may not be the driver of differing contaminant levels between colonies. Levels of persistent pollutants in the Gannet eggs fall below most existing thresholds for adverse effects and are within internationally reported values. Recent population growth and range expansion of Gannets in Ireland suggest that persistent pollutants are not having an immediate impact on the Gannet population. This study will inform potential monitoring programmes that can help Ireland achieve good environmental status under the European Union’s Marine Strategy Framework Directive.

The ecotoxicology of surfactants is attracting wide attention due to the rapidly expanding global application. As interspecific relationships play one of the central roles in structuring biological communities, it is necessary to take it into risk assessments on surfactants. With this aim, our study investigated the interference of three common surfactants on the inducible defense of a freshwater phytoplankton Scenedesmus obliquus. Nonlethal environmentally relevant concentrations (10 and 100 μg L⁻¹) of several surfactants were set up. Results showed that growth and photosynthetic efficiency of Scenedesmus were inhibited during first 96 h, but recovered in the later stage. Surfactants interfered inducible defense of Scenedesmus against Daphnia grazing, and the interference was related to chemical characteristics of surfactants. The anionic surfactant sodium dodecyl sulfate (SDS) enhanced the colony formation even without grazing cues, whereas fewer defensive colonies were formed under the effects of cationic surfactant benzalkonium bromide (BZK) and nonionic surfactant polyoxyethylene (40) nonylphenol ether (NPE). These findings highlighted the sensitivity of grazer-induced morphological defense of Scenedesmus to surfactants even at nonlethal concentrations, which potentially affects the energy and information flow between trophic levels. This study appeals for more attention to take interspecific relationships into consideration in assessing the potential ecological risk of pollutants.

Cyanobacterial blooms are an increasing problem in a more eutrophic world. It is still a challenge to fully understand the influence of cyanobacteria on the interactions between predator and prey at higher trophic levels. The present study was mainly undertaken to understand the inducible anti-predator responses of cladocerans while using cyanobacteria as part of food. Specifically speaking, we focused on the anti-predator strategies of Ceriodaphnia cornuta in response to different predators (fish and Chaoborus larvae) under food with different proportions of Microcystis aeruginosa. The morphological (i.e., body size and the induction of horns) and life history traits (e.g., time to first reproduction, offspring number, and survival time) responses were measured under different proportions of M. aeruginosa (i.e., 0%, 20%, 40%, 60%, 80%, and 100%). Our results showed that both the life history and the inducible anti-predator responses of C. cornuta were significantly affected by different concentrations of M. aeruginosa. Specifically, lower concentrations of Microcystis (20%–60%) can significantly promote the horns induction under Chaoborus predation risks, and higher Microcystis concentrations (60%–100%) tend to enhance reproduction in response to fish predation risks, such as larger body size, decreased time to first reproduction, and increased total offspring number. Additionally, an increasing concentration of M. aeruginosa decreased the ability of C. cornuta to reverse horns when predation risks removed. Our findings indicated that cyanobacteria affecting life history traits and the subsequent indirect effects on anti-predator responses in cladocerans could impact the interactions between predator and prey at higher trophic levels and may consequently contribute to shaping the structure of the community in a cyanobacteria bloom area.

Assessing the fate of both legacy and newer persistent organic pollutants (POPs) is an ongoing challenge. Top predators, including seabirds, are effective monitors of POPs because they forage over a range of marine habitats, integrating signals over space and time. However, migration patterns can make unravelling contaminant sources, and potentially assessments of the effectiveness of regulations, challenging if chemicals are acquired at distant sites. In 2014, we fitted geolocators on ancient murrelets (Synthliboramphus antiqueus) at four colonies on the Pacific Coast of Canada to obtain movement data throughout an annual cycle. All birds underwent a post-breeding moult in the Bering Sea. Around one-third then returned to overwinter on the British Columbia (BC) coast while the rest migrated to overwinter in waters along the north Asian coast. Such a stark difference in migration destination provided an opportunity to examine the influence of wintering location on contaminant signals. In summer 2015, we collected blood samples from returned geo-tagged birds and analyzed them for a suite of contaminants, including polybrominated diphenyl ethers (PBDEs), non-PBDE halogenated flame retardants, perfluoroalkyl substances (PFASs), organochlorines, and mercury. Feathers were also collected and analyzed for stable isotopes (δ¹³C, δ¹⁵N, and δ³⁴S). We found no significant differences in blood concentrations of any contaminant between murrelets from the two different overwinter areas, a result that indicates relatively rapid clearance of POPs accumulated during winter. Spatial variation in diet (i.e., δ¹³C) was associated with both BDE-47 and -99 concentrations. However, individual variation in trophic level had little influence on concentrations of any other examined contaminants. Thus, blood from these murrelets is a good indicator of recent, local contaminants, as most signals appear independent of overwintering location.

The Atrato watershed is a rainforest that supports exceptional wildlife species and is considered one of the most biodiversity-rich areas on the planet, currently threatened by massive gold mining. Aimed to protect this natural resource, the Constitutional Court of Colombia declared the river subject to rights. The objective of this study was to quantify trace elements in sediments and fish from Atrato watershed, assessing their environmental and human health risk. Forty-two trace elements were quantified using ICP-MS. Thirty-one elements increased their concentration downstream the river. Concentration Factors (CF) suggest sediments were moderately polluted by Cr, Cu, Cd, and strongly polluted by As. Most stations had Cr (98%) and Ni (78%) concentrations greater than the Probable Effect Concentration (PEC) criteria. Together, toxic elements generate a Pollution Load Index (PLI) and a Potential Ecological Risk Index (RI) that categorized 54% of the sediments as polluted, and 90% as moderate polluted, respectively. Hemiancistrus wilsoni, a low trophic guild fish species, had the greater average levels for Ni, Cu, As and Cd, among other elements. Rubidium and Cs showed a positive correlation with fish trophic level, suggesting these two metals biomagnify in the food chain. The Hazard Quotient (HQ) for As was greater than 1 for several species, indicating a potential risk to human health. Collectively, data suggest gold mining carried out in this biodiversity hotspot releases toxic elements that have abrogated sediment quality in Atrato River, and their incorporation in the trophic chain constitutes a large threat on environmental and human health due to fish consumption. Urgent legal and civil actions should be implemented to halt massive mining-driven deforestation to enforce Atrato River rights.

The Mediterranean basin is a hotspot of mercury (Hg) contamination owing to intense anthropogenic emissions, volcanic activity and oligotrophic conditions. Little work has been done to assess the sources of Hg exposure for seabirds and, particularly, the physiological consequences of Hg bioaccumulation. In this study, we (i) describe the individual and temporal variation in blood concentration of total Hg (THg) over three breeding seasons, (ii) identify the factors that affect the THg exposure and (iii) determine the individual- and population-level connections between THg and blood-based markers of oxidative status in chicks of Scopoli’s shearwaters (Calonectris diomedea) breeding on the island of Linosa in the southern Mediterranean. We carried out the work on chicks near fledging because they are fed with prey captured near the colony, thus their Hg levels reflect local contamination. The concentration of THg in erythrocytes varied from 0.23 to 4.29 μg g⁻¹ dw. Chicks that were fed upon higher trophic level prey (i.e., higher δ¹⁵N values) had higher THg levels. Individual variation in THg concentrations was not explained by parental identity, sex nor δ¹³C values. There was significant variation in THg among chicks born from the same mother in different years. We found significant correlations between THg and markers of oxidative status; however, these correlations were no longer significant when we took into account the annual variation in mean values of all metrics. Males with higher values of body condition index had higher blood THg, while THg and body condition index were not correlated in females. Our data indicate that THg levels were moderate to high if compared to other seabirds. However, there is little evidence for harmful short-term detrimental effects owing to THg exposure.