Climate Trivia: Coral Bleaching
Some of Earth’s most diverse and colorful ecosystems are shallow-water coral reef ecosystems, which are built on the skeletons of animals called corals. One critical part of these ecosystems, known as zooxanthellae – the single- celled organisms that live in coral skeletons – use their photosynthetic ability to manufacture sugars from the sun, which they give to the corals. This energy, which could be likened to “rent” paid, is necessary to keep the corals alive and the reef ecosystems functioning. Corals need warm waters to survive, which is why they are only found in tropical and subtropical waters. If the water becomes too warm, however, corals “expel” the zooxanthellae and “bleach.” While corals can recover from bleaching events if the exceptionally warm conditions wane, periods of prolonged exposure to these conditions cause the corals to die. When waters in the reefs rise 1.6 degrees Fahrenheit above their long-term monthly averages, they are considered by the National Oceanic and Atmospheric Administration to be in danger of bleaching. El Niño years correspond to elevated sea surface temperatures on a global scale and the El Niño events of 1982-83 and 1997-1998 corresponded to years when coral bleaching was especially widespread.
Trivia Question: During the severe global coral bleaching event of 1998, what percentage of the world’s reef-building corals died?
a. One percent
b. Ten percent
c. 16 percent
d. Less than one percent
The correct answer is c. Sixteen (16) percent of Earth’s corals died during the 1998 bleaching event. Sea surface temperatures in the tropical and sub-tropical Atlantic are the warmest they have been since record keeping began in the 1880’s. The northern hemisphere summer (June, July and August) of 2009 logged the warmest summer global sea-surface temperatures on record.
(Sources: National Oceanic and Atmospheric Administration: NOAA News. “NOAA: Warmest Global Sea Surface Temperatures for August and Summer.” 16 September 2009. Accessed Online 6 February 2010 <http://www.noaanews.noaa.gov/stories2009/20090916_globalstats.html> and Government of Australia: Great Barrier Reef Marine Park Authority. “What is Coral Bleaching?” Accessed Online 6 February 2010 <http://www.gbrmpa.gov.au/corp_site/key_issues/climate_change/climate_change_and_the_great_barrier_reef/what_is_coral_bleaching>)