Biotransport of metallic trace elements from marine to terrestrial ecosystems by seabirds

Seabird transported contaminants are dispersed in island ecosystems

Seabirds are long-range transporters of nutrients and contaminants, linking marine feeding areas with terrestrial breeding and roosting sites. By depositing nutrient-rich guano, which acts as a fertiliser, seabirds can substantially influence the terrestrial environment in which they reside. However, increasing pollution of the marine environment has resulted in guano becoming similarly polluted. Here, we determined metal and metalloid concentrations (As, Cd, Cr, Cu, Hg, Pb) in Flesh-footed Shearwater (Ardenna carneipes) guano, soil, terrestrial flora, and primary consumers and used an ecological approach to assess whether the trace elements in guano were bioaccumulating and contaminating the surrounding environment. Concentrations in guano were higher than those of other Procellariiformes documented in the literature, which may be influenced by the high amounts of plastics that this species of shearwater ingests. Soil samples from shearwater colonies had significantly higher concentrations of all metals, except for Pb, than soils from control sites and formerly occupied areas. Concentrations in terrestrial primary producers and primary consumers were not as marked, and for many contaminants there was no significant difference observed across levels of ornithogenic input. We conclude that Flesh-footed Shearwaters are transporters of marine derived contaminants to the Lord Howe Island terrestrial environment.

Yellow-legged gull populations (Larus michahellis) link the history of landfills to soil eutrophication and time-related vegetation changes on small Mediterranean islands

Seabird colonies have a strong influence on both the physical and chemical soil parameters and plant communities of the islands where they settle to nest. Scientists have studied the effects of the demographic explosion of seabird populations, but few have explored the long-term effects when the colonies were in decline. The aim of this study was to investigate diachronic changes over a 24 year period of soil parameters, floristic composition and plant functionnal types (Raunkiaer growth forms and Grime life strategies) up to the decrease of the number of nesting yellow-legged gulls (Larus michahellis Naumann, 1840) on Mediterranean islands. We used 78 permanent plots to survey the vegetation and the soil parameters on 9 islands and one mainland area within the Calanques National Park (south east of France), for three periods (i.e., 1997, 2008, 2021). Since 1997, the increase of nesting gulls has caused a nitrogen and pH increase and organic carbon and C/N ratio decrease, although the values were still higher than mainland plots without nesting gulls. This has led to changes in plant species composition e.g., higher values of N favouring the development of ruderal plant species, still present in high frequency in 2021. Furthermore, plant species highly tolerant to disturbances (i.e., R Grime strategy) in harsh environments were still favoured even after the decline of gull abundance. However, both the frequency of the chamaephytes and the vegetation cover has increased with the decline of gull colony. In 2021, measures of trace elements' concentrations and calculation of pollution load index (Cu, Pb and Zn) reveals relatively low multi-contamination levels on the mainland and the archipelagos. On naturally oligotrophic and semi-arid Mediterranean islands, gull colonies induce a persistent alteration in soil characteristics that still influences plant communities (composition and functional types), 11 years after the decline in bird abundance.

Scavenging gulls are biovectors of mercury from industrial wastes in Nova Scotia, Canada

Seabirds are important biovectors of contaminants, like mercury, moving them from marine to terrestrial environments around breeding colonies. This transfer of materials can have marked impacts on receiving environments and biota. Less is known about biotransport of contaminants by generalist seabirds that exploit anthropogenic wastes compared to other seabird species. In this study, we measured total mercury (THg) in O-horizon soils at four herring gull (Larus smithsoniansus) breeding colonies in southern Nova Scotia, Canada. At colonies with dry substrate, THg was significantly higher in soils collected from gull colonies compared to nearby reference soils with no nesting gulls. Further, THg was distinct in soils among study colonies and was likely influenced by biotransport from other nesting seabird species, most notably Leach's storm-petrels (Hydrobates leucorhous). Our research suggests gulls that scavenge on anthropogenic wastes at local industrial sites are biovectors moving THg acquired at these sites to their colonies and may increase the spatial footprint of contaminants from these industries.

The influence of seabirds on their breeding, roosting, and nesting grounds: a systematic review and meta-analysis

Seabird species worldwide are integral to both marine and terrestrial environments, connecting the two systems by transporting vast quantities of marine-derived nutrients and pollutants to terrestrial breeding, roosting, and nesting grounds via the deposition of guano and other allochthonous inputs (e.g., eggs, feathers). We conducted a systematic review and meta-analysis and provide insight into what types of nutrients and pollutants seabirds are transporting, the influence these subsidies are having on recipient environments, with a particular focus on soil, and what may happen if seabird populations decline. The addition of guano to colony soils increased nutrient levels compared to control soils for all seabirds studied, with cascading positive effects observed across a range of habitats. Deposited guano sometimes led to negative impacts, such a guanotrophication, or guano-induced eutrophication, which was often observed where there was an excess of guano or in areas with high seabird densities. While the literature describing nutrients transported by seabirds is extensive, literature regarding pollutant transfer is comparatively limited, with a focus on toxic and bioaccumulative metals. Research on persistent organic pollutants and plastics transported by seabirds is likely to increase in coming years. Studies were limited geographically, with hotspots of research activity in a few locations, but data were lacking from large regions around the world. Studies were also limited to seabird species listed as Least Concern on the IUCN Red List. As seabird populations are impacted by multiple threats and steep declines have been observed for many species worldwide, gaps in the literature are particularly concerning. The loss of seabirds will impact nutrient cycling at localised levels and potentially on a global scale as well, yet it is unknown what may truly happen to areas that rely on seabirds if these populations disappear.

Biomonitoring metals and metalloids in wild mammals: invasive versus non-invasive sampling

Heavy metal and metalloid pollution is a matter of concern in animal, human and environmental health (One Health) and also in wildlife conservation worldwide. Studying wild mammals in toxicology has been contributing significantly to our knowledge, namely to find out the most critical regions, to understand bioaccumulation and biomagnification phenomena or to evaluate their toxic effects. However, not all the animal tissues and organs provide the same information or should be interpreted in the same way. The best sample to use will depend on the objectives and conditions of the study. This review aims to compare invasive and non-invasive samples to biomonitor heavy metals, providing a brief resume of their advantages, limitations and examples of use. Further research, using a wider range of mammalian species, is required to establish what information can be obtained in biomonitoring studies that use non-invasive samples (such as hair, faeces and parasites) and/or invasive samples (such as blood, liver, kidney, bone and other organs).

Geolocators link marine mercury with levels in wild seabirds throughout their annual cycle: Consequences for trans-ecosystem biotransport

Seabirds are widely used as indicators of marine pollution, including mercury (Hg), because they track contaminant levels across space and time. However, many seabirds are migratory, and it is difficult to understand the timing and location of their Hg accumulation. Seabirds may obtain Hg thousands of kilometers away, during their non-breeding period, and deposit that Hg into their terrestrial breeding colonies. We predicted that Hg concentration in rectrices reflects exposure during the previous breeding season, in body feathers reflects non-breeding exposure, and in blood collected during breeding reflects exposure during current breeding. To test this hypothesis, we measured total Hg concentration in these three tissues, which reflect different timepoints during the annual cycle of rhinoceros auklets (Cerorhinca monocerata) breeding on both sides of the North Pacific (Middleton Island in Alaska and Teuri Island in Hokkaido), and tracked their wintering movement patterns with biologging devices. We (i) identify the wintering patterns of both populations, (ii) examine Hg levels in different tissues representing exposure at different time periods, (iii) test how environmental Hg exposure during the non-breeding season affects bird contamination, and (iv) assess whether variation in Hg levels during the non-breeding season influences levels accumulated in terrestrial plants. Individuals from both populations followed a figure-eight looping migration pattern. We confirm the existence of a pathway from environmental Hg to plant roots via avian tissues, as Hg concentrations were higher in plants within the auklet colonies than at control sites. Hg concentrations of breast feathers were higher in Alaskan than in Japanese auklets, but Hg concentrations in rectrices and blood were similar. Moreover, we found evidence that tissues with different turnover rates could record local anthropogenic Hg emission rates of areas visited during winter. In conclusion, Hg was transported across thousands of kilometers by seabirds and transferred to local plants.

Seabird breeding islands as sinks for marine plastic debris

Seabirds are apex predators in the marine environment and well-known ecosystem engineers, capable of changing their terrestrial habitats by introducing marine-derived nutrients via deposition of guano and other allochthonous inputs. However, with the health of the world's oceans under threat due to anthropogenic pressures such as organic, inorganic, and physical pollutants, seabirds are depositing these same pollutants wherever they come to land. Using data from 2018 to 2020, we quantify how the Flesh-footed Shearwater (Ardenna carneipes) has inadvertently introduced physical pollutants to their colonies on Lord Howe Island, a UNESCO World Heritage site in the Tasman Sea and their largest breeding colony, through a mix of regurgitated pellet (bolus) deposition and carcasses containing plastic debris. The density of plastics within the shearwater colonies ranged between 1.32 and 3.66 pieces/m² (mean ± SE: 2.18 ± 0.32), and a total of 688,480 (95% CI: 582,409-800,877) pieces are deposited on the island each year. Our research demonstrates that seabirds are a transfer mechanism for marine-derived plastics, reintroducing items back into the terrestrial environment, thus making seabird colonies a sink for plastic debris. This phenomenon is likely occurring in seabird colonies across the globe and will increase in severity as global plastic production and marine plastic pollution accelerates without adequate mitigation strategies.

Geolocator tagging links distributions in the non-breeding season to population genetic structure in a sentinel North Pacific seabird

We tested the hypothesis that segregation in wintering areas is associated with population differentiation in a sentinel North Pacific seabird, the rhinoceros auklet (Cerorhinca monocerata). We collected tissue samples for genetic analyses on five breeding colonies in the western Pacific Ocean (Japan) and on 13 colonies in the eastern Pacific Ocean (California to Alaska), and deployed light-level geolocator tags on 12 eastern Pacific colonies to delineate wintering areas. Geolocator tags were deployed previously on one colony in Japan. There was strong genetic differentiation between populations in the eastern vs. western Pacific Ocean, likely due to two factors. First, glaciation over the North Pacific in the late Pleistocene might have forced a southward range shift that historically isolated the eastern and western populations. And second, deep-ocean habitat along the northern continental shelf appears to act as a barrier to movement; abundant on both sides of the North Pacific, the rhinoceros auklet is virtually absent as a breeder in the Aleutian Islands and Bering Sea, and no tagged birds crossed the North Pacific in the non-breeding season. While genetic differentiation was strongest between the eastern vs. western Pacific, there was also extensive differentiation within both regional groups. In pairwise comparisons among the eastern Pacific colonies, the standardized measure of genetic differentiation (Fꞌ_ST) was negatively correlated with the extent of spatial overlap in wintering areas. That result supports the hypothesis that segregation in the non-breeding season is linked to genetic structure. Philopatry and a neritic foraging habit probably also contribute to the structuring. Widely distributed, vulnerable to anthropogenic stressors, and exhibiting extensive genetic structure, the rhinoceros auklet is fully indicative of the scope of the conservation challenges posed by seabirds.

Converting Ecological Currencies: Energy, Material, and Information Flows

Understanding how the three currencies of life - energy, material, and information - interact is a key step towards synthesis in ecology and evolution. However, current theory focuses on the role of matter as a resource and energy, and typically ignores how the same matter can have other important effects as a carrier of information or modifier of the environment. Here we present the hypothesis that the dynamic conversion of matter by organisms among its three currencies mediates the structure and function of ecosystems, and that these effects can even supersede the effects of matter as a resource. Humans are changing the information in the environment and this is altering species interactions and flows of matter within and among ecosystems.

Influence of overwinter distribution on exposure to persistent organic pollutants (POPs) in seabirds, ancient murrelets (Synthliboramphus antiquus), breeding on the Pacific coast of Canada

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.

Seabird-Transported Contaminants Are Reflected in the Arctic Tundra, But Not in Its Soil-Dwelling Springtails (Collembola)

Arctic-breeding seabirds contain high levels of many anthropogenic contaminants, which they deposit through guano to the tundra near their colonies. Nutrient-rich soil in vicinity to seabird colonies are favorable habitats for soil invertebrates, such as springtails (Collembola), which may result in exposure to seabird-derived contaminants. We quantified a wide range of lipid-soluble and protein-associated environmental contaminants in two springtail species (Megaphorura arctica and Hypogastrura viatica) and their respective habitats (soil/moss) collected underneath seabird cliffs. Although springtails are commonly used in laboratory toxicity tests, this is the first study to measure concentrations of persistent organic pollutants (POPs) and mercury (Hg) in springtails from the field, and to study biotransportation of contaminants by seabirds to soil fauna. We categorized the sites a priori as of low, medium, or high seabird influence, based on the seabird abundance and species composition. This ranking was reflected in increasing δ¹⁵N values in soil/moss and springtails with increasing seabird influence. We found clear indications of seabirds impacting the terrestrial soil environments with organic contaminants, and that concentrations were higher in soil and moss close to the bird cliff, compared to farther away. However, we did not find a relationship between contaminant concentration in springtails and the concentrations in soil/moss, or with level of seabird influence. Our study indicates a low uptake of contaminants in the soil fauna, despite seabird-derived contamination of their habitat.