Trophic relationships among Antarctic fulmarine petrels:insights into dietary overlap and chick provisioning strategies inferred from stable-isotope (d15N and d13C) analyses

Abstract

We used stable-isotope analysis (SIA) to evaluate trophc relationships in an Antarctic seabird community. We deterrnined natural abundances of stable-nitrogen (St5N) and stable-carbon (613C) isotopes from blood samples (n = 283) from adults and chicks of 4 Antarctic fulrnarine petrel species (Fulmarus glaciaioides, Thalassoica antarctica, Daption capense and Pagodroma nivea) during 2 consecutive breeding seasons, 1994/1995 and 1995/1996, and from representative prey items. Our objectives were to use the isotope approach to infer trophic Status and diet composition within and between species, addressing interspecific and temporal variability within this seabird community, and to investigate potential age-related differences in assumed trophic position within species. Prey 613C values ranged from -26.8% in amphipods to -23.9% in adult Antarctic silverfish. Seabird St3C values ranged from -25.3 Yw in Antarctic petrel chicks to -23.8760 in Cape petrel adults. Prey 6I5N values ranged from 4.0Yw in euphausiids to 10.7Yw in adult Antarctic silverfish. Seabird 615N values ranged from 8 . 4 7~ in Antarctic petrel adults to 12.0%0 in Snow petrel chicks. There was considerable interspecific overlap in assumed trophic positions amongst the 4 petrel species, and we conclude aii species consumed fish and krill. Despite this apparent overlap, the range in 615N values for petrels corresponded to the equivalent of 1 full trophic level, and estimated trophic level varied with both species and age. A simple trophic level model, constructed based on the 615N data, predicted trophic levels ranging from 2.3 in krill to 4.7 in Snow petrel chicks. Snow petrels and Antarctic fulrnars tended to have higher 615N values than Antarctic and Cape petrels, suggesting a higher proportion of fish in their diets. Petrel chicks consistently had higher 615N values than adults, which suggests trophic segregation between adults and chcks. We discuss advantages of selectively provisioning chcks with higher trophic level prey. Extensive overlap and a relatively narrow range of 615N values are consistent with a food web comprised of few trophic steps.

Occurrence, bioaccumulation and long-range transport of short-chain chlorinated paraffins on the Fildes Peninsula at King George Island, Antarctica

“…Trophic levels (TLs) in biota samples were determined using the following equation (Hodum and Hobson, 2000):…”

Parent–offspring dietary segregation of Cory’s shearwaters breeding in contrasting environments

“…Chicks often exhibit higher d 15 N signatures than adults, usually between 1.0 and 2.0 %, and these age differences are often quoted as an indication that adult fed their chicks with higher-trophic-level prey than they assimilated themselves (Hodum and Hobson 2000;Cherel et al 2005aCherel et al , 2008Forero et al 2005;Richoux et al 2010). Age differences in d 13 C signatures do not present any obvious trend and generally are of a smaller magnitude (less than 1 %) (Hodum and Hobson 2000;Forero et al 2005;Cherel et al 2008Bond et al 2010;Richoux et al 2010; but see Cherel et al 2005a). The uncritical interpretation of differences in chick and adult isotope levels as evidence of dietary segregation may present some problems, as explained below.…”

“…Nitrogen stable isotopes increase in a predictable manner between trophic levels and thus indicate the trophic position of consumers (Kelly 2000;Bearhop et al 2004). Recently, SIA has provided evidence for a dietary segregation between adults and chicks in a wide range of pelagic seabirds (Hodum and Hobson 2000;Forero et al 2005;Cherel et al 2005aCherel et al , 2008Bond et al 2010;Richoux et al 2010). However, most of the mentioned studies could not assess the biological significance of the isotopic differences between adults and growing chicks (but see Cherel et al 2005a;Forero et al 2005) as isotopic fractionation differs between them, as a result of growth or nutritional stress effects (Williams et al 2007;Sears et al 2009).…”

Abrupt recent shift in δ 13 C and δ 15 N values in Adélie penguin eggshell in Antarctica

“…Since the 1980s, carbon (␦ 13 C) and nitrogen (␦ 15 N) stable isotope values of seabird tissues have been used to address questions on diet and foraging behavior (10)(11)(12)(13)(14). These studies are particularly useful when traditional diet studies (observations of chick feedings and stomach lavage) are difficult to carry out on far-ranging species such as many seabirds.…”