Common Eider and Herring Gull as Contaminant Indicators of Different Ecological Niches of an Urban Fjord System
Authors: Thorstensen Helene , Ruus Anders , Helberg Morten , Bæk Kine , Enge Ellen Katrin , Borgå Katrine 
Published: September 2020

Abstract
Seabirds like gulls are common indicators in contaminant monitoring. The herring gull (Larus argentatus) is a generalist with a broad range of dietary sources, possibly introducing a weakness in its representativeness of aquatic contamination. To investigate the herring gull as an indicator of contamination in an urban-influenced fjord, the Norwegian Oslofjord, we compared concentrations of a range of lipophilic and protein-associated organohalogen contaminants (OHCs), Hg, and dietary markers in blood (n = 15), and eggs (n = 15) between the herring gull and the strict marine-feeding common eider (Somateria mollissima) in the breeding period of May 2017. Dietary markers showed that the herring gull was less representative of the marine food web than the common eider. We found higher concentrations of lipophilic OHCs (wet weight and lipid weight) and Hg (dry weight) in the blood of common eider (mean ± SE ∑PCB = 210 ± 126 ng/g ww, 60 600 ± 28 300 ng/g lw; mean Hg = 4.94 ± 0.438 ng/g dw) than of the herring gull (mean ± SE ∑PCB = 19.0 ± 15.6 ng/g ww, 1210 ± 1510 ng/g lw; mean Hg = 4.26 ± 0.438 ng/g dw). Eggs gave opposite results; higher wet weight and lipid weight OHC concentrations in the herring gull (mean ± SE ∑PCB = 257 ± 203 ng/g ww, 3240 ± 2610 ng/g lw) than the common eider (mean ± SE ∑PCB = 18.2 ± 20.8 ng/g ww, 101 ± 121 ng/g lw), resulting in higher OHC maternal transfer ratios in gulls than eiders. We suggest that the matrix differences are due to fasting during incubation in the common eider. We suggest that in urban areas, herring gull might not be representative as an indicator of marine contamination but rather urban contaminant exposure. The common eider is a better indicator of marine pollution in the Oslofjord. The results are influenced by the matrix choice, as breeding strategy affects lipid dynamics regarding the transfer of lipids and contaminants to eggs and remobilization of contaminants from lipids to blood during incubation, when blood is drawn from the mother. Our results illustrate the benefit of a multispecies approach for a thorough picture of contaminant status in urban marine ecosystems. Integr Environ Assess Manag 2021;17:422–433. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC)
KEY POINTS
The common eider, a benthic midtrophic predator, represents marine contamination in the urban Oslofjord marine food web better than the opportunistic herring gull, but it cannot replace the gull as the indicator species. The herring gull feeds from terrestrial and anthropogenic sources in addition to the marine food web, and it shows lower blood OHC concentrations than the common eider, but it is an interesting indicator species for the urban environment. Egg-to-blood ratio OHC concentration ratios were &gt;0 in the gull and &lt;0 in the eider, likely resulting from remobilization of contaminants to the bloodstream during the incubation fast in eiders, providing challenges for interpreting results, and illustrating that the matrices should be used in combination. There was no clear species difference in PFAS concentrations, with higher concentrations of PFDA, PFUdA, and PFHxS in the common eider, higher PFTrDA concentrations in the herring gull, and no difference between the species for PFOS and PFDoA.