Trophic signatures of seabirds suggest shifts in oceanic ecosystems

Gagne, Tyler; Hyrenbach, K. David; Hagemann, Molly E.; Houtan, Kyle S. Van

doi:10.1126/sciadv.aao3946

Cited by 37 publications

(44 citation statements)

References 56 publications

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“…The TL of seabirds in the Hawaiian archipelago has declined broadly over 125 years. These TL trends from fishery-independent data align with fisheries-dependent studies (Pauly et al 1998, Pauly and Watson 2005, Essington et al 2006, and appear driven by commercial fisheries extraction and climate change (Gagne et al 2018a(Gagne et al , 2018b. Beyond chronological shifts, contemporary comparisons of two tropical tern populations across three ocean basins highlight geographical within-species variability, and confirm that seabirds within areas of greatest fishing intensity feed at lower TLs (Gagne et al 2018a).…”

Section: Introductionsupporting

confidence: 57%

“…Published studies (Gagne et al 2018a(Gagne et al , 2018b and their open-access repositories (osf.io/h8bmg/, osf.io/4s9ty/) provide extensive details on the habitats and TLs for all species as well as the raw data used from those studies.…”

Section: Sample Collection and Heavy Metal Assaymentioning

confidence: 99%

“…Seabirds are often highly-migratory, fish-eating predators that broadly integrate food webs across large geographic distances into their tissues (Furness and Camphuysen 1997, Finkelstein et al 2007, Abbasi et al 2015, Bond et al 2015, Gagne et al 2018b. As a result, many seabird species are useful indicators of the dynamics of marine food webs.…”

Section: Introductionmentioning

confidence: 99%

“…Seabirds are also readily accessible for study, either in large nesting colony aggregations, through ongoing stranding programs, or in natural history repositories. Museums and other collections, for example, may contain large historical specimen archives, and these specimens can help generate a long-term record of ecosystem dynamics (Vo et al 2011, Wiley et al 2012, Wiley et al 2013, Ostrom et al 2017, Gagne et al 2018a, 2018b. The changes in heavy metal concentrations in seabird tissues over time could document broad changes in environmental contamination, either from the proliferation of industrial applications or in response to regulatory efforts to reduce their pollution (Hosono et al 2010, Hosono et al 2011.…”

Section: Introductionmentioning

confidence: 99%

“…While TLs may be expected to vary between species, TLs are also dynamic within species and can vary across space and time. Recent studies, for example, show that the TLs at which seabirds now feed are significantly below their historical preferences (Gagne et al 2018a(Gagne et al , 2018b, reflecting much broader trends of ecosystem chain length compression (Estes et al 2011). The TL of seabirds in the Hawaiian archipelago has declined broadly over 125 years.…”

Section: Introductionmentioning

confidence: 99%

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Coupled trophic and contaminant analysis in seabirds through space and time

Gagne

Johnson

Hyrenbach

et al. 2019

Environ. Res. Commun.

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Wildlife contaminant loads are often used to indicate ecosystem health, but their interpretation is complicated by the dynamics affecting the trophic transfer of toxins. Yet, coupled analyses of trophic position and contaminants may provide insights that help resolve the underlying signal of contaminants in ecosystems. Here, we analyze heavy metal concentrations and trophic positions for pelagic seabirds across time and space. We derive metal-specific trophic transfer coefficients from the literature and use them to interpret the changes in raw heavy metal concentrations in two settings: (i) for eight seabird species across a 125-year timeline in Hawaii, and (ii) for contemporary specimens of two tern species across three ocean basins. While previous studies report how trophic position varies in these two settings, here we investigate how trophic downgrading may affect the observed raw changes in contaminants. Using this approach, we find the highly-toxic metal elements (Hg, As, Pb) decline after 1980. However, several other metals (Cu, Mn, Mo, Cd, Fe) increase from 1990-2015. Though simultaneous biomagnification and trophic downgrading may obscure contaminant analyses across space and time, the trophic declines we observed (0.5 trophic level) are likely not sufficient to influence such comparisons. In addition, as extrapolating contaminant concentrations across broad ranges of trophic levels may be prone to large uncertainties, careful selection of the focal species for analysis is required. While high trophic level species, such as long-lived, fish-eating seabirds, are ideal for monitoring environmental contaminants across large spatial or time scales, lower trophic level species, like primary producers and consumers, may be more suitable for quantifying the concentrations of bio-available contaminants entering the marine ecosystem and the base of the marine food webs. Monitoring low and high trophic levels simultaneously may provide an integrated perspective that is needed to quantify the contaminants entering and bio-magnifying through marine ecosystems.

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Section: Introductionsupporting

confidence: 57%

Section: Sample Collection and Heavy Metal Assaymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Coupled trophic and contaminant analysis in seabirds through space and time

Gagne

Johnson

Hyrenbach

et al. 2019

Environ. Res. Commun.

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Emaciated enigma: Decline in body conditions of common dolphins in the Celtic Seas ecoregion

Albrecht,

Minto,

Rogan

et al. 2024

Ecology and Evolution

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Monitoring the nutritional health of cetaceans has become increasingly important in a changing environment, where multiple stressors impact animals. Particularly for those species that require consumption of energy‐dense prey, such as the common dolphin. Thus far, no uniform measure for monitoring body condition has been recommended across cetaceans, and species‐specific measures may need to be developed if employed as a population condition indicator under Descriptor 1 of the Marine Strategy Framework Directive. Here, nine morphometric body condition indices were applied to long‐term common dolphin stranding data sets originating from Ireland and the UK. We report a recent decline in the nutritional health of common dolphins in the Celtic Seas ecoregion comparing animals from 2017 to 2019 to animals from 1990 to 2006, with an increase in cases of animals dying due to starvation. Using ordinal regression trees, ventral blubber thickness (VBT) was identified as the most important index to predict nutritional status, defined at necropsy, followed by the scaled mass index (SMI). Using generalised linear models, both the VBT and SMI indices differentiated individuals that died from chronic and acute causes of death (i.e., bycatch), where animals in chronic conditions had significantly thinner VBT and lower SMI. Both significant temporal and seasonal patterns in VBT were identified, with poorer body conditions observed during the autumn and better body conditions observed during the spring, as well as an overall decline detected in VBT during the study period. While VBT was positively correlated with total body length, SMI showed the opposite trend. The VBT index is recommended for monitoring nutritional health within the species when total body length and season are considered. Further research is needed to understand the underlying causes for the observed decline, including shifts in prey availability and/or quality, to inform targeted conservation management strategies.

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