Its terrestrial and marine ecology and oceanographic conditions are quite distinct from other Southern Ocean islands, including Australia’s other subantarctic island, Macquarie Island.
HIMI is the only major subantarctic island group believed to contain no species directly introduced by humans, making it among the most biologically pristine areas on the planet.
The islands and surrounding waters provide crucial breeding habitat for a range of birds and marine mammals, including many species listed as threatened and/or migratory under the international conservation agreements and the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act). Two species of bird, the Heard Island sheathbill and the Heard Island cormorant, are endemic to the Reserve.
The terrestrial environment displays distinctive geographical features such as permanent glaciers, Australia’s only active volcanoes, and Australia’s highest mountain (Mawson Peak 2750 m) outside the Australian Antarctic Territory.
Heard Island also contains significant cultural relics and heritage sites from 19th and early 20th century sealing activities and from the first Australian Antarctic research expeditions.
The marine environment surrounding the islands features diverse and distinctive benthic habitats that support a range of slow growing and vulnerable species including corals, sponges, barnacles and echinoderms.
The waters of the Reserve also include prime foraging areas for a number of land-based marine predators, and provide nursery areas for a range of fishes, including commercially harvested fish species.
Areas of highly productive nutrient rich waters in the Reserve, created by the confluence of key oceanographic fronts such as the Antarctic Polar Front, are believed to provide suitable feeding grounds for a range of cetaceans.
The key conservation values of the HIMI region were documented in the report Conservation of marine habitats in the region of Heard Island and McDonald Islands (PDF).