WWF reports coral bleaching underway in American Samoa

Posted on 20 March 2003

Coral bleaching is occurring at all of WWF's seven research sites in American Samoa, including reefs within marine protective areas.
Further bleaching may occur elsewhere in the Pacific Washington DC, US - WWF today reported that coral bleaching is occurring at all of its seven research sites in the US territory of American Samoa, including reefs within the protective boundaries of the US National Park of American Samoa, Fagatele Bay National Marine Sanctuary, and Maloata Bay community reserve. “The bleaching that we’re seeing at WWF research sites in American Samoa indicates that in the face of climate change, reef conservation will require more complex responses than the creation of protected areas alone,” said Dr Lara Hansen, primary investigator for the WWF research project. “Coral reefs are diverse ecosystems that are not only beautiful but are crucial to human economies and food supplies. Depending on its extent, an episode of coral bleaching can dramatically damage or even lead to the death of a reef.” Up to 30 per cent of the coral reef has bleached at Maloata Bay, with most other sites experiencing between 10–20 per cent bleaching. When corals are exposed to stressful conditions, they bleach — losing the colourful symbiotic algae that are necessary to their continued health and survival. Coral bleaching can occur when the coral is exposed to water temperatures above their normal thermal maxima — an increase of as little as 1 or 2°C. The coral rely on the algae for the energy they produce via photosynthesis. This leaves the coral in an energy deficit and, without recolonization by the symbiotic algae, the coral can die. Remote sensing and on-site monitoring showed water temperatures increasing 1.5°C above the normal annual high temperature at the reefs in American Samoa for six weeks proceeding the WWF surveys. These reefs are still experiencing warm water conditions and it is not possible to predict when water temperatures will drop or how much additional bleaching will occur. From 1876–1979 only three bleaching events were recorded globally, while 60 are on record from 1980 until 1993. While localized bleaching events can be caused by isolated stress factors, such as altered salinity and siltation, the common thread in large-scale bleaching events is elevated temperature. This increase in bleaching frequency has been linked to global warming-related increases in annual sea surface temperature and occurrences of El Niño-Southern Oscillation events. The rate of occurrence and almost global scale since the early 1980s is in stark contrast to the trend of the first half of the century, where bleaching events were localized and linked to local events. Despite the waning condition of this year’s El Niño-Southern Oscillation event, remarkably warm water is present in the Southern Pacific. It is therefore possible that further bleaching events will occur in the region. WWF research sites throughout the Pacific are now monitoring for bleaching. In the last two decades, global warming, which is caused by human-induced emissions of carbon dioxide and other gases that blanket the world and trap in heat, has emerged as a significant threat to coral reefs, with large areas of reefs dying off due to coral bleaching. Coral bleaching has been particularly severe in the Indian Ocean, where as much as 50–95 percent of all corals died during the 1997–98 El Niño-Southern Oscillation event. “The damage occurring among coral reefs in US territories in the South Pacific underscores the urgent need for the United States to implement existing solutions that reduce carbon dioxide emissions, such as using clean renewable energy and energy efficient technologies,” said Katherine Silverthorne, director of WWF’s US Climate Change Programme. For further information: Kathleen Sullivan Director, WWF-US Climate Change Programme Tel: +1 202 778 9576 E-mail: kathleen.sullivan@wwfus.org
Bleached coral in American Samoa.
© WWF / Eric Mielbrecht