The introduced green crab (Carcinus maenas) as a novel food resource for the opportunistic kelp gull (Larus dominicanus) in Argentine Patagonia

YORIO, PABLO; SUÁREZ, NICOLÁS; KASINSKY, TATIANA; POLLICELLI, MIRIAM; IBARRA, CYNTHIA; GATTO, ALEJANDRO

Aquatic Invasions

REABIC

Lugar: Helsinki; Año: 2020 vol. 15 p. 140 - 159

Introduced speciesare one of the main threats to biological diversity, but they can alsofacilitate native species through mechanisms such as trophic subsidy. Wequantified the diet of breeding kelp gulls (Larus dominicanus) and theirconsumption of the introduced green crab (Carcinus maenas) at five colonieslocated along over 600 km of coastline in Patagonia, Argentina, and analyzeddifferences in consumption rates among breeding locations. Results based onpellet analysis (n = 961 pellets) showed that kelp gulls consumed green crabsduring most or part of the breeding cycle at all study locations (0?73.9%,depending on location, year and breeding stage). Green crab consumptiondiffered among breeding locations, with lower consumption further from the reportedlocation of first Argentinean introduction (Golfo San Jorge, Chubut, Patagonia)in 1999?2000. Despite kelp gulls regularly consumed green crabs at mostbreeding locations, this invasive species was not an important component intheir diet. Both stomach content and stable isotope analyses from breeding kelpgulls indicated that the main prey were fish such as Argentine anchovy andArgentine hake (Engraulis anchoita and Merluccius hubbsi, respectively) andsquat lobster (Munida gregaria). At Isla Vernaci Este and Punta Tombo, greencrabs were found in only one stomach of all kelp gull age classes sampled(incubating adults (n = 42), young chicks (n = 75), and old chicks (n = 105)).Based on carbon and nitrogen isotopic values from blood samples from incubatingadults (n = 54), Bayesian mixing model outputs showed that green crabscontributed 7.3?23.9% to the overall diet. The study showed that the relativelyrecent introduction of green crabs supplements the available prey base of awidely distributed and abundant predator, the kelp gull, at least during itsbreeding season in a large coastal sector of central Patagonia. The extent towhich the kelp gull in coastal Patagonia may be shaping the establishment,abundance, and population dynamics of the introduced green crab is stillunknown and will require further research.