Variability in trophic level and habitat use in response to environmental forcing: isotopic niche dynamics of breeding seabirds in the southeastern Bering Sea

Abstract

Climate-driven changes in the marine environment may affect inter-and intraspecific resource partitioning by marine organisms. When and how resources are partitioned may depend on access to diverse foraging habitats. Here we examined the variability in the isotopic niche of breeding seabirds with respect to trophic level and habitat use in years with cold and warm sea temperatures in the Bering Sea. Between 1999 and 2015 (n = 12 yr), we collected blood from blacklegged kittiwakes Rissa tridactyla, and common Uria aalge and thick-billed murres U. lomvia breeding on St. George and St. Paul Islands on the southeastern Bering Sea continental shelf. We examined isotopic niche dynamics at the group and species levels. Stable isotope values of blood tissues corroborated published observations of seabird distributions in the region. All 3 species increased foraging on shelf-based prey during warm oceanographic conditions, in contrast to a higher reliance on oceanic-based prey during cold conditions. Under warm ocean conditions, the isotopic niche of the seabird group with access to only shelf habitat (St. Paul Island) contracted, whereas the isotopic niche of the seabird group with access to shelf, slope, and basin habitats (St. George Island) expanded. These group-level responses were associated with increased food availability. We conclude that habitat heterogeneity in the vicinity of breeding colonies may mediate how predators partition food resources in response to changes in climate-driven food availability.

Sympatric Atlantic puffins and razorbills show contrasting responses to adverse marine conditions during winter foraging within the North Sea

“…How animals respond to changing environmental conditions is a key topic in movement and foraging ecology. Mobile predators may potentially respond to changes in prey availability by moving to find new resources or switching diets [1, 11, 42, 43, 45, 50, 70]. The nature of any such response reflects a balance of risk/reward associated with resource intake, energetic costs and physiological demands.…”

“…Like many other seabirds, annual survival rates of adult auks are typically high ( c. 0.90) with most mortality occurring in winter [28]. Ecological and environmental conditions during winter moult therefore have the potential to influence the distribution, behaviour and mortality of seabirds, but the majority of studies on environmental influences on diet and distributions of seabirds have focussed on impacts during the breeding season [30, 54, 70]. Considerably less information is available regarding changes occurring outside the breeding season.…”

Opposing effects of spatiotemporal variation in resources and temporal variation in climate on density dependent population growth in seabirds

“…Direct studies of this mechanism in seabirds are rare. However, three species of seabirds breeding in the southeastern Bering Sea shifted their dietary niche in response to changing environmental conditions, measured using sea temperatures, and this shift was mediated by their ability to access spatially heterogeneous foraging habitats (Kokubun et al, 2018 ; Will & Kitaysky, 2018 ). Foraging habitat variation does, therefore, appear to be a valid mechanism allowing breeding seabirds to exploit changing prey availability in relation to climatically driven oceanographic changes, and to potentially buffer against periods of low food availability through access to diverse habitats and spatial variation in forage resources.…”

Wintering in the Western Subarctic Pacific Increases Mercury Contamination of Red-Legged Kittiwakes

“…Head feathers were washed in a 2:1 chloroform methanol solution, cut into small pieces, and packed in tin capsules. Samples were analyzed either at the Light Stable Isotope Lab at the University of California Santa Cruz (2011) or at the University of Alaska Fairbanks Stable Isotope Facility (UAF 2014–17). , The two laboratories were comparable . Stable isotope ratios are reported in delta notation as parts per thousand (‰) relative to the international standard δ 15 N air as follows: δ 15 N = [( R sample / R standard ) – 1] ‰, where R is the corresponding ratio of 15 N/ 14 N. Internal standards pugel (UCSC) and pepton (UAF) were within ±0.01‰.…”