flora and fauna. Subantarctic island example The physical landscape and biota communities of Heard Island and McDonald Islands are constantly changing due to volcanism, strong winds and waves, and climate change. Volcanic activity has been observed in this area since the mid-1980s, with fresh lava flows on the southwest flanks of Heard Island. Satellite imagery shows that McDonald Island increased in size from about 1 to 2.5 square kilometers between 1994 and 2004, as a result of volcanic activity. In addition to new land being produced by volcanism, global warming of the climate is causing the retreat of glaciers on the islands (see section below ). These combined processes produce new ice-free terrestrial and freshwater ecoregions, such as moraines and lagoons, which are now available for colonization by plants and animals. Heard Island has vast colonies of penguins and petrels, and large harems of land-based marine predators such as elephant seals and fur seals. Due to the very high numbers of seabirds and marine mammals on Heard Island, the area is considered a "biological hot spot". The marine environment surrounding the islands features diverse and distinctive benthic habitats that support a range of species including corals, sponges, barnacles and echinoderms. This marine environment also serves as a nursery area for a range of fishes, including some species of commercial interest. Retreat of subantarctic glaciers Glaciers are currently retreating at significant rates throughout the southern hemisphere. With respect to glaciers of the Andes mountains in South America, abundant evidence has been collected from ongoing research at Nevado del Ruiz in Colombia, Quelccaya Ice Cap and Qori Kalis Glacier in Peru, Zongo, Chacaltaya and Charquini glaciers in Bolivia, the Aconcagua River Basin in the central Chilean Andes, and the Northern Patagonian and Southern Patagonian ice fields. Retreat of glaciers in New Zealand and Antarctica is also well documented. Many subantarctic glaciers are also in retreat. Mass balance is significantly negative on many glaciers on Kergeulen Island, Heard Island, South Georgia and Bouvet Island. Glaciers of Heard Island Heard Island is a heavily glacierized, subantarctic volcanic island located in the Southern Ocean, roughly 4000 kilometers southwest of Australia. 80% of the island is covered in ice, with glaciers descending from 2400 meters to sea level. Due to the steep topography of Heard Island, most of its glaciers are relatively thin (averaging only about 55 meters in depth). The presence of glaciers on Heard