Beyond that, they expel the colourful food-producing zooxanthellae algae in a process called bleaching. If it is too warm for too long, bleached corals die. High water temperatures in 1997 and 1998 sparked unprecedented bleaching in all major tropical regions. Meanwhile, polar regions suffer worse biological impacts than lower latitudes. Sea ice is diminishing in both the Arctic and Antarctic, depriving wildlife of hunting and breeding grounds.
Sea ice is habitat for the algae at the base of the polar food web.
As ice shrinks, so does the food available at higher levels on the web, from zoo-plankton to seabirds. In the Antarctic, air temperatures have been increasing since the 1950s, causing significant stress for species that depend on sea ice. Both eat the same prey, but Adelies winter on sea ice, while chinstraps prefer open water. Populations of crabeater seals, which also require pack ice, are falling, while southern fur, southern elephant, and other open-water seals are extending their ranges further south. Researchers in western Hudson Bay have documented decreased weight in adult polar bears and a decline in the birthrate since the early 1980s.