The effect of long-range transport, trophic position and diet specialization on legacy contaminant occurrence in great skuas, Stercorarius skua, breeding across the Northeast Atlantic

Abstract

High levels of halogenated organic contaminants (HOCs) have been found in the marine predatory seabird great skua (Stercorarius skua) from breeding colonies in the Northeastern Atlantic, with large unexplained inter-colony variation. The present study aimed at analyzing if the HOCs occurrence in breeding great skuas in remote colonies was explained by local baseline food web exposure determined by long-range transport, or by ecological factors such as diet specialization and relative trophic position in the breeding area. The occurrence of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) was analyzed in plasma of 204 adult great skuas collected over two years (2008 and 2009) and 5 colonies across the North-Atlantic from Shetland to Svalbard. The ΣHOCs levels in plasma ranged across two orders of magnitude, from 40 to 7600 ng/g (wet weight) and differed significantly across the great skua colonies. The variation in contaminant occurrence among colonies did not reflect long-range transport through a latitudinal or remoteness gradient, as the second northernmost colony (Bjørnøya), had the highest contaminant concentrations. No latitudinal or remoteness gradient was evident in the contaminant pattern among the colonies. The contaminant levels increased significantly with increasing δ 15 N values, and regurgitated pellets of undigested prey suggested that great skuas with higher δ 15 N values had a higher proportion of bird prey in their diet, mostly seabirds. In contrast, great skuas from colonies with lower δ 15 N and lower contaminant level fed mostly on fish. The enrichment of δ 13 C increased with decreasing δ 15 N and lower contaminant levels. Therefore, individual behavior of great skuas, such as migration strategies and diet specialization, rather than long-range transport and thus baseline food web exposure, explain among and within colony variance in contaminant occurrence.

Differences in Trophic Level, Contaminant Load, and DNA Damage in an Urban and a Remote Herring Gull (Larus argentatus) Breeding Colony in Coastal Norway

“…In comparison to the remote herring gulls, the diet of gulls nesting close to human settlements shows a different diet which includes anthropogenic waste, terrestrial invertebrates, mammals, and plants (Ewins et al, 1994 ; Laurich et al, 2019 ; Mendes et al, 2018 ). The larger size of the remote Hornøya females compared to urban Oslofjord gulls can also explain the difference observed in trophic level, because larger gulls can predate on birds and larger fish, both food sources leading to higher δ 15 N values (Leat et al, 2019 ; Nogales et al, 1995 ).…”

Combined threats of climate change and contaminant exposure through the lens of bioenergetics

“…Furthermore, vulnerability may be higher in long‐lived species due to bioaccumulation (Burger & Gochfeld, 2004), and in species and populations occupying habitats or areas that serve as contaminant sinks (e.g., the Arctic; agricultural fields). Individuals may also differ in contaminant exposure due to feeding specialization and differences in spatial movement (Leat et al, 2019; Saaristo et al, 2018).…”

On the evolution of trophic position

“…Heritable behavioural traits, such as boldness, activity levels or prey selectivity, could also prove to be important determinants of trophic position variation. For example, intraspecific variation in the predatory seabird Stercorarius skua (great skua) likely arises from dietary specialisation (fish vs. seabirds), which in turn affects the levels of contamination with biomagnifying pollutants (Leat et al, 2019 ). However, previous reviews of such behavioural traits highlight the ongoing challenge of quantifying both their heritability and their role as determinants of individual diet variation (Araújo et al, 2011 ; Bengston et al, 2018 ; Sih & Bell, 2008 ).…”

“…Directional selection gradients for trophic position could result from biomagnification of organochlorine pollutants in food webs (Kiriluk et al, 1995 ; Vander Zanden & Rasmussen, 1996 ). If there is a positive correlation between the trophic position of organisms in a food web and pollutant concentration in tissues, then individual predators might face fitness costs when feeding on organisms at higher trophic levels (Leat et al, 2019 ). This could lead to negative selection gradients for trophic position within such predator populations.…”