Diet analysis of Alaska Arctic snow crabs (Chionoecetes opilio) using stomach contents and δ13C and δ15N stable isotopes

Abstract

We used stomach content and stable δ 13 C and δ 15 N isotope analyses to investigate male and female snow crab diets over a range of body sizes (30-130 mm carapace width) in five regions of the Pacific Arctic (southern and northern Chukchi Sea, western, central, and Canadian Beaufort Sea). Snow crab stomach contents from the southern Chukchi Sea were also compared to available prey biomass and abundance. Snow crabs consumed four main prey taxa: polychaetes, decapod crustaceans (crabs, amphipods), echinoderms (mainly ophiuroids), and mollusks (bivalves, gastropods). Both approaches revealed regional differences. Crab diets in the two Chukchi regions were similar to those in the western Beaufort (highest bivalve, amphipod, and crustacean consumption). The Canadian Beaufort region was most unique in prey composition and in stable isotope values. We also observed a trend of decreasing carbon stable isotopes in crabs from the Chukchi to those in the Canadian Beaufort, likely reflecting the increasing use of terrestrial carbon sources towards the eastern regions of the Beaufort Sea from Mackenzie River influx. Cannibalism on snow crabs was higher in the Chukchi regions relative to the Beaufort regions. We suggest that cannibalism may have an impact on recruitment in the Chukchi Sea via reduction of cohort strength after settlement to the benthos, as known from the Canadian Atlantic. Prey composition varied with crab size only in some size classes in the southern Chukchi and central Beaufort, while stable isotope results showed no size-dependent differences. Slightly although significantly higher mean carbon isotope values for males in the

Sipunculan fauna in the Pacific Arctic region: a significant component of benthic infaunal communities

“…In such an eventuality, sipunculans may play a larger role as a walrus prey item. Similarly, sipunculans are among the favored food prey for the snow crab (Chionoecetes opilio) in the Pacific Arctic, although not the first choice (Divine et al 2017). Demersal feeding fish are also known to prey on sipunculans.…”

“…In the Pacific Arctic two important sipunculan consumers have been identified: the walrus (Sheffield et al 2001;Sheffield and Grebmeier 2009) and crabs (e.g., the snow crab; Divine et al 2017); however, fish and gastropods can prey on sipunculans as well (Kohn 1975). Sipunculans are a potentially nutritious food item: the mean energy (caloric) content of G. margaritacea was reported to be 18.42 MJ kg -1 but can also reach as high a value as 21.47 MJ kg -1 , which is similar to the caloric content of amphipods-an important food item for gray whales, but lower than the caloric content of bivalves and polychaetes, which are often preyed upon by walruses (Wilt et al 2014;Wilt pers.…”

“…They are mainly deposit feeders, and usually transform particulate organic matter (microalgae, protista, meiofauna, detritus, fecal pellets) from the water column, sediment surface or sediment itself (Murina 1984), but some species may also filter-feed (Gibbs 1977). In turn, sipunculans are preyed upon by cephalopods, sea anemones, crabs (Fischer 1925;Divine et al 2017), gastropods and fish (Kohn 1975), and marine mammals, such as walruses (Sheffield et al 2001;Sheffield and Grebmeier 2009).…”

Size-frequency distribution, growth, and mortality of snow crab (Chionoecetes opilio) and arctic lyre crab (Hyas coarctatus) in the chukchi sea from 2009 to 2013

“…Small bivalves, like Macoma calcarea and Ennucula tenuis were listed as dominant in the benthic macrofaunal biomass while amphipods dominated by abundance, possibly allowing higher abundances of immature crabs around Hanna Shoal (Grebmeier et al, 2015b). It is also known that compared to other regions in the Alaskan Arctic, C. opilio in the southern and northern Chukchi Sea had a relatively high frequency of occurrence of brachyuran crabs, possibly juvenile C. opilio, in their diet composition (Divine et al, 2015). Habitat segregation in the Chukchi Sea on the basis of food availability and feeding behavior is therefore likely but further studies like diet composition of immature C. opilio (≤34 mm CW) in the Chukchi Sea are necessary to draw this conclusion.…”

“…They are found over a wide depth range, with C. opilio occurring between 30-1400 m water depth at year round bottom water temperatures of −1.5 to 4°C (Dawe and Colbourne, 2002), and H. coarctatus occurring between 2 and 457 m water depth and a similar temperature range as C. opilio (Bryant, 1991). Both species are found on muddy or sandy grounds, and are carnivorous, cannibalistic and opportunistic feeders, preying on gastropods, ophiuroids, crustaceans, bivalves and polychaetes with polychaetes, bivalves and amphipods being the more frequently consumed prey items by C. opilio in the Chukchi Sea (Bryant, 1991;Dawe and Colbourne, 2002;Divine et al, 2015;Ernst et al, 2005;Kolts et al, 2013;Wieczorek and Hooper, 1995a). …”