Impacts of global warming on corals

Corals become "bleached" when water temperatures rise too high and are sustained for too ... rel=
Corals become "bleached" when water temperatures rise too high and are sustained for too long. Fiji.
© Cat HOLLOWAY / WWF-Canon

Coral reefs bleaching to death

Coral reefs around the world have been severely damaged by unusually warm ocean temperatures.

Coral reefs are extremely important for biodiversity, providing a home to over 25% of all marine life. They are also vital for people and business. They provide nurseries for many species of commercially important fish, protection of coastal areas from storm waves, and are a significant attraction for the tourism industry.

However, coral reefs are very fragile sensitive ecosystems that can only tolerate a narrow temperature range.

What is coral bleaching?

One of the most visually dramatic effects of climate change on corals has been bleaching. When the ocean warms, the oxygen content reduces, and corals become ‘bleached’.

The heat affects the tiny algae which live symbiotically inside the corals and supply them with food. The heat stress damages the algae and in consequence leads to coral death.

Global warming could now mean a death sentence for many coral reefs. If the present rate of destruction continues, most of the world's coral reefs could be killed within our lifetime.

More information

Coral bleaching due to temperature rise, Indo-Pacific Ocean. / ©: WWF-Canon / Jürgen FREUND
Coral bleaching due to temperature rise, Indo-Pacific Ocean.
© WWF-Canon / Jürgen FREUND

Coral bleaching events

The Seychelles Islands are justly famous for their coral reefs and the remote Aldabra Atoll is the largest raised atoll in the world. Despite its remoteness and protected status, the Seychelles suffered a severe coral bleaching event in the late 1990s and a recent assessment by the Seychelles Foundation judged climate change to be the most significant threat facing the atoll.

In March 2003, WWF reported that coral bleaching was occurring at all its 7 research sites in American Samoa, including within the National Park of American Samoa, Fagatele Bay National Marine Sanctuary and Maloata Bay Community Reserve.
Coral reef destroyed by Crown of Thorn starfish or by coral bleeching. Great Barrier Reef & ... / ©: WWF-Canon / Jürgen FREUND
Coral reef destroyed by Crown of Thorn starfish or by coral bleeching. Great Barrier Reef & Coral Sea, Australia.
© WWF-Canon / Jürgen FREUND

Take action to save our coral reefs

Local conservation actions alone will not be sufficient to protect coral reefs from the effects of climate change.

Our only real hope of rescuing the coral reefs from the damaging effects of climate change depends on limiting the temperature increase by the end of this century to less than 2°C. If we do something now, we may be able to help ensure that there are coral reefs left for future generations to appreciate.

Other global warming effects could also threaten coral reefs

    • More frequent tropical storms caused by global warming could break up the coral.
    • Unusually warm water (by up to 5°C) caused by more frequent El Niño years, would also be an additional stress.
    • More frequent heavy rains means more flooding, more river runoff, and therefore more sediment deposit in the seas.
    • Finally, climate change could also reduce the ability of corals to form their limestone skeletons.

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