A comparison of the trophic ecology of Beaufort Sea Gadidae using fatty acids and stable isotopes

Abstract

Polar cod (Boreogadus saida) is one of the most studied Arctic marine fishes given its circumpolar distribution and centralised role in the Arctic marine food web. In contrast, relatively little is known about two other Arctic Gadidae: saffron cod (Eleginus gracilis) and Greenland cod (Gadus ogac). Climate change is expected to have an effect on sea ice-associated species, such as polar cod, but due to our lack of knowledge of other arctic gadid species it remains unclear how climate change will impact them and their interactions within the arctic marine ecosystem. Here, we explored the ecology of three Arctic Gadidae that co-occur in the Canadian Beaufort Sea. Stable isotope (SI) (niche overlap) and fatty acid (FA) (correspondence analysis and linear discriminant analysis) biomarkers were used to assess among-and within-species differences and trophic niche. Despite the close habitat proximity of saffron cod and polar cod while on the shelf, trophic niche characterisation revealed only a marginal overlap. Marginal niche overlaps also occurred for the two coastal species with similar diets, saffron cod and Greenland cod, likely reflecting regional-scale differences between two habitats. Within-species, polar cod collected from three habitats (shelf, upper-and lower-slope habitats) were not differentiated likely due to the movement of individuals between habitats. In contrast, Greenland cod had a narrow trophic niche and differentiation occurred between the two collection sites. The comparison of trophic niches defined by stable isotope and fatty acid proved a promising tool for new insights into the ecology of Arctic fishes.

The Canadian Beaufort Shelf trophic structure: evaluating an ecosystem modelling approach by comparison with observed stable isotopic structure

“…Knowledge of the roles and significance of many resident marine species for ecosystem structure and function remains limited (Cobb et al 2008), but has recently improved as a result of ecosystem modelling exercises and dedicated ecosystem studies (e.g. Loseto et al 2009;Connelly et al 2014;Bell et al 2016;Brewster et al 2016Brewster et al , 2017Giraldo et al 2016;Majewski et al 2016a;Stasko et al 2016;Hoover et al 2021). Detailed descriptions of CBS ecosystem structure can be found elsewhere (Carmack and Macdonald 2002;Cobb et al 2008), but we provide a brief overview here for context in light of recent investigations.…”

“…Michel, unpublished data). Data for beluga whales, coastal marine fishes, and anadromous fishes were provided by the Arctic Coastal Ecosystem Study (Brewster et al, 2016;Brewster et al, 2017), and various other riverine and coastal sampling programs (Tran 2014;McNicholl et al, 2018;M. Power and J. Reist, unpublished data).…”

Cod movement ecology in a warming world: Circumpolar arctic gadids

“…For example, using C and N stable isotopes and fatty acids, Brewster et al. (2018) found minimal trophic overlap among B. saida , saffron cod and Greenland cod ( Gadus ogac , Gadidae) in the Beaufort Sea indicating these species partition resources through occupying distinct habitats. Moreover, a lack of differentiation in trophic niche among B. saida sampled in shelf, upper and lower slope habitats was attributed to movement of individuals among habitats and feeding on prey across this depth gradient.…”

“…Until relatively recently, the movement ecology of fishes in the Arctic was determined primarily by fisheries catch data and the gut contents of predators (Hollowed et al., 2013). More advanced techniques, however, are now providing biological and physiological support to observed species' distributions and movement behaviours, including chemical tracers to infer diet and foraging location (Brewster et al., 2018) and analysis of antifreeze protein structure to understand adaptation to extreme environments (Devries & Cheng, 2005; Fletcher et al., 2001; Præbel & Ramløv, 2005). Physiological constraints on movements are further being explored through controlled laboratory experiments examining thermal tolerance (Drost et al, 2014; Drost, Fisher et al, 2016; Drost, Lo et al, 2016), temperature‐dependent growth and swim speed (Laurel et al., 2016; Schurmann & Christiansen, 1994), and metabolic rate (Kunz et al., 2016).…”

Habitat degradation increases interspecific trophic competition between three spiny lobster species in Seychelles

“…Typically, a species' niche size can be used as a proxy for the diversity of biochemically distinct prey eaten by this species (i.e., J o u r n a l P r e -p r o o f 5 intraspecific variability), while the probability of overlap between two species gives indications on the degree of similarity of the biochemical composition of their prey (i.e., interspecific variability) (Costa-Pereira et al 2019). Many studies successfully combined SI and FA to study trophic overlap between co-occurring species (e.g., Connan et al 2014;Sardenne et al 2016;Brewster et al 2017).…”