Black Guillemots in A Melting Arctic: Responding to Shifts in Prey, Competitors and Predators.

Abstract

—Arctic species closely associated with snow and ice habitats will be among the first to be affected by rising atmospheric temperatures. The Black Guillemot (Cepphus grylle mandti) is a high-arctic seabird nesting in ground-level cavities in northern Alaska and feeding in and next to the arctic pack ice. Since 1975 the species has been studied annually at a colony in northern Alaska. Observations of breeding phenology and success found that temperature-induced changes in snow and sea ice habitats recently allowed the species to colonize the region but now are preventing successful reproduction. Black Guillemots did not breed in northern Alaska until the late 1960s, when warming temperatures allowed access to nest cavities for the 80 days needed for successful reproduction. During the 1970s and 1980s, guillemots thrived as summer length continued to increase and arctic pack ice remained within the 40 km foraging range of breeding colonies, allowing access to adult Arctic Cod (Arctogadus glacialis) associated with sea ice. Continued increases in temperature and resulting reductions in summer pack extent in the late 20th and early 21st Century resulted in decreased nesting success by modifying the distribution and abundance of guillemot prey, competitors, and predators. As availability of adult Arctic Cod decreased with summer ice extent, parents turned to smaller cod and lower-quality benthic prey to provision young, leading to brood reduction and lower fledging weights. Decreasing ice also allowed the Horned Puffin (Fratercula corniculata), a subarctic seabird, to colonize the region and compete with guillemots for nest cavities. Prospecting puffins now regularly kill up to half of the guillemot nestlings. Lastly, Polar Bears (Ursus maritimus), abandoning the summer sea ice as it retreats off the continental shelf, swim to the island where they eat guillemot eggs and nestlings, causing almost complete nesting failures in the past three years. Breeding success of guillemots is currently insufficient to maintain a breeding population in the region. These observations of rapid changes in an apex predator supported by the cryopelagic ecosystem demonstrate some of the biological effects of the well-documented reductions in summer extent of the arctic pack ice. Similar or related effects are likely influencing ice-associated vertebrate populations throughout the Arctic Basin and will reach a critical threshold with the predicted disappearance of summer ice later in this century. Transcribed from oral presentation given on 1 Feb-