The potential effects of marine habitat change on Antarctic seabirds
Article first published online: 23 SEP 2004
Volume 146, Issue Supplement s1, pages 90–91, September 2004
How to Cite
Croxall, J. P. (2004), The potential effects of marine habitat change on Antarctic seabirds. Ibis, 146: 90–91. doi: 10.1111/j.1474-919X.2004.00332.x
- Issue published online: 23 SEP 2004
- Article first published online: 23 SEP 2004
- Received 25 April 2002; revision accepted 1 July 2002.
The continent of Antarctica and the waters of the Southern Ocean surrounding it have substantial influence on regional and global climate processes. The principal mechanisms relate to:
- 1long-term patterns of change in sea and air temperature and ice extent, relating to the annual cycle of advance and retreat of sea ice and to the melting of ice shelves;
- 2longer distance links arising from the Southern Ocean acting as the connection between the Atlantic, Indian and Pacific Oceans, and the influence of north-flowing Antarctic bottom water on global climate and ocean/atmosphere links to tropical and more temperate processes such as the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO).
Many of these processes also contribute to generation of the nutrient-rich conditions that sustain some of the world's greatest concentrations of seabirds and seals, principally along the Antarctic Peninsula and on the sub-Antarctic Islands. Holocene palaeoclimate records and ornithogenic soil profiles and contents indicate substantial fluctuations in the presence, abundance and diet of Adelie Penguins Pygoscelis adeliae, consequent upon warming events and linked ice/glacier retreats over the last 6000 years. More recently, the successive removal of fur seals, whales and some fish species have caused major food-web perturbations. Nevertheless, the current rate of change in the climate of Antarctica suggests an unprecedented potential for changes to oceanographic processes that affect top predators like seabirds.
However, very few Antarctic/sub-Antarctic bird species depend on intertidal habitats and would therefore be immediately vulnerable to rising sea-level. Nevertheless, sea-level rise could adversely affect Kelp Gull Larus dominicanus (specializing in limpets) and two regional endemics, the Antarctic Pipit Anthus antarcticus (a strandline forager in winter) and South Georgia Pintail Anas georgica (virtually confined to beaches and bays in winter when its tussock and pond habitats are snow- and ice-covered). Sheathbills Chionis spp., a family endemic to the Antarctic, also favour coastal habitats, but their versatile feeding habits (particularly as scavengers on seal and seabird colonies) and the migratory habit of the Greater Sheathbill Chionis alba should preclude any serious consequences of sea-level rise.
Species restricted to life within a few kilometres of shorelines, such as Gentoo Penguin Pygoscelis papua and members of the Blue-eyed Shag Phalacrocorax atriceps agg. complex, have deep-diving capacity (to 100–150 m), linked to exploiting chiefly bentho-pelagic prey. The vertical amplitude of their niche is likely to preclude most of the envisaged effects of habitat change in the region, except that they depend to some extent on prey advected into their habitat.
The many species of albatross and petrel breeding mainly at sub-Antarctic islands are usually regarded as wide-ranging across oceanic habitats. However, recent satellite-tracking studies have shown that many if not most of these species, although having vast ranges, actively forage in restricted parts of these, characterized by particular bathymetric and/oceanographic features and conditions. Shelves and shelf margins are of particular importance to some species (e.g. most penguins, Black-browed Albatross Thalassarche melanophrys, White-chinned Petrel Procellaria aequinoctialis) whereas frontal regions, especially the Antarctic Polar Front, are particularly important for Grey-headed Albatross Thalassarche chrysostoma and King Penguin Aptenodytes patagonicus. This greatly increases the likelihood that changes in nutrient availability in upwelling and frontal areas and/or shifts in oceanographic domains could have important consequences for species inhabiting sub-Antarctic islands, which cannot easily move their breeding sites as productive habitats and conditions change. From 20 years of monitoring studies at South Georgia, there is already evidence from the reproductive performance of predators of a significant change in average levels of prey (especially krill) availability and of an increased frequency of years of very low breeding success. However, the major impacts are likely to affect the ice-associated species of the Antarctic Continent and the Marginal Ice Zone (MIZ). Species extensively and/or seasonally dependent on the latter habitat (e.g. Adelie Penguin, Snow Petrel Pagodroma nivea, Light-mantled Albatross Phoebetria palpebrata, Short-tailed Shearwater Puffinus tenuirostris) may be positively (if continental breeders) or negatively (if sub-Antarctic breeders) affected by a southward shift and/or reduction in extent of the MIZ. Because of the key role of the MIZ in the reproduction and recruitment of Antarctic Krill Euphausia superba, potential changes here may also, with other oceanographic domain changes, contribute to a shift away from krill-dominated trophic pathways to those favouring copepods and mesopelagic fish, especially lantern fish Myctophidae. This would have basin-, even ocean-, wide consequences for higher predators, including seabirds.
For species extensively dependent on fast ice and associated polynya (areas of open water) (e.g. Snow Petrel, Antarctic Petrel Thalassoica antarctica, Emperor Penguin Aptenodytes forsteri), changes in the duration and persistence of ice cover and of polynya could have serious consequences, even in the relatively short term. Information on the biology of such species is inadequate to assess which changes would have the most important demographic consequences. For Emperor Penguins, however, their need for persistent polynya during winter incubation, and for suitable fast ice during chick-rearing and for the autumn moult indicates significant potential vulnerability at most stages of their annual cycle and several stages of their life cycle.
Although most of the Antarctic marine avifauna is likely to be able to persist or adapt, the effects on certain high-latitude ice-associated species and on others of already unfavourable conservation status (e.g. most albatrosses, some petrels and penguins) could be serious on fairly short time scales. As it is unrealistic to expect direct mitigation and management action of the effects of climate change on marine systems, this places a premium on action now in respect of highly precautionary sustainable use of existing resources (including minimizing other sources of anthropogenic mortality (e.g. fishery by-catch)), to reduce the risk of potential instability in Antarctic marine food webs.
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