Antarctic environmental change and biological responses

Abstract

Antarctica and the surrounding Southern Ocean are facing complex environmental change. Their native biota has adapted to the region's extreme conditions over many millions of years. This unique biota is now challenged by environmental change and the direct impacts of human activity. The terrestrial biota is characterized by considerable physiological and ecological flexibility and is expected to show increases in productivity, population sizes and ranges of individual species, and community complexity. However, the establishment of non-native organisms in both terrestrial and marine ecosystems may present an even greater threat than climate change itself. In the marine environment, much more limited response flexibility means that even small levels of warming are threatening. Changing sea ice has large impacts on ecosystem processes, while ocean acidification and coastal freshening are expected to have major impacts.

Fig. 1. Map of Antarctica, showing locations mentioned in the text, and the Southern Ocean, showing ice-covered and ice-free areas shallower than 200 m, 200- to 1000-m depth, and deeper than 1000 m [modified from (21); image provided by P. Fretwell, British Antarctic Survey].

Fig. 2. Satellite images of the area surrounding the original Larsen B ice shelf.

(A) Ice-covered area in 2000 before its collapse, and (B) in March 2004/5, showing chlorophyll (chl) concentrations from the dense phytoplankton bloom that was present in the newly exposed area (white areas were sea ice covered and gave no signal) [from (266)]. SeaWIFS (Sea-Viewing Wide Field-of-View Sensor) is a satellite borne sensor for measuring Chlorophyll in surface ocean waters; MODIS (Moderate Resolution Imaging Spectroradiometer)is an instrument monitoring the Earth’s atmosphere, ocean, and land surface with a set of visible, NIR, MIR, and thermal channels run by NASA.

Fig. 3. Illustration of the major threats to Antarctic biodiversity in the coming century.

Clockwise from top left: Warming reduces ice cover both in the sea and on land, which, combined with increased human activity, makes the establishment of non-native species much more likely (images are the invasive midge E. murphyi, and the noted but not established marine seaweed U. intestinalis and crab H. araneus); the reduction in sea ice and increased variability affects species dependent on sea ice for habitat, notably krill that are a key ecosystem resource for many penguins, seals, and whales [images are humpback whale, krill, copepod (Calanus propinquus), and emperor penguin chicks]; low-mobility (and many with limited dispersal) marine species affected by multiple factors, including warming, acidification, freshening, increased sedimentation, etc. [images are brachiopods (Liothyrella uva), nemertean worms (Parborlasia corrugatus), anemones (Isotaelia antarctica), and giant isopod (Glyptonotus antarcticus)]; large increases in human activity in terms of more infrastructure, increased tourism, and national field campaigns all directly affect environments on land and sea (images are Dash 7 aircraft, McMurdo station, tourist vessel, Rothera station building, Sir David Attenborough ship, and vehicle tracks on King George Island); reductions in coastal ice make new habitat for new biological productivity in the water column and on the seabed, acting to provide new food for ecosystems and against warming by sequestering carbon; warming, ice melt, and increased precipitation on the continent not only provide new ice-free areas and stimulate increases in populations of native species but also increase likelihood of establishment of non-natives and reduce the isolation and, hence, persistence of native species. Colors on continent show warming and cooling trends over the past 50 years: Red intensity shows warming up to 2°C, and blue shows cooling of up to −1.5°C [following (195)].