A recent study of Australia’s Great Barrier Reef brought to light how extensively coral bleaching has affected this natural marvel, and it has the world wondering just what is causing this devastating problem. The Great Barrier Reef, famous for its beautiful corals, colorful marine creatures and massive size, stretches for 1,429 miles along Australia’s northeastern coastline. A shocking 93% of the reef is classified as suffering from some amount of coral bleaching (McKirdy). This is a huge increase from 2002, when the amount of the reef suffering from coral bleaching was observed to be only about 60% (GBRPA). The National Coral Bleaching Taskforce reported that in some areas the coral’s death toll reached up to 90%, including older, slower growing corals that could take decades to return to these areas (McKirdy). Coral bleaching is making an appearance in reefs all over the world, and conservationists are worried. Not only do reef habitats help support fisheries and other marine life, they protect the mainland by absorbing major waves created by storms. One of Australia’s biggest concerns regarding coral bleaching is its effect on tourism, which accounts for $3.9 billion of revenue and 70,000 jobs (McKirdy).
What is Coral Bleaching?
Corals have a very beneficial mutual relationship with tiny marine algae, called zooxanthellae, which live inside polyps found in corals’ tissues and help them to survive. Zooxanthellae are food producers and supply corals with 90% of the energy that they need to grow, reproduce and live (GBRPA). Coral bleaching transpires when the relationship between coral and its zooxanthellae, which also give coral much of their color, starts to break down due to a variety of reasons. When this breakdown happens, the tissue of the actual coral animal begins to look transparent in the absence of the zooxanthellae and the white skeleton making up the coral’s structure is exposed (GBRPA). As stated before, zooxanthellae are major food producers for corals, so when the zooxanthellae are expelled, corals bleach and then begin to starve. Although some corals are able to feed themselves, most struggle to survive without their zooxanthellae partners.
On a positive note, it is possible for corals to recover their zooxanthellae, return to their normal color and continue to survive if conditions steadily improve. However, the stress previously put on recovering bleached coral commonly causes a decrease in coral growth and reproduction, in addition to an increased susceptibility to disease (GBRPA). Bleached corals generally die if stressful conditions persist and zooxanthellae cannot return to their coral hosts. Even if conditions do improve, reefs with extensive coral bleaching and death can take many, many years to recover and thrive again.
What Causes Coral Bleaching?
Coral bleaching is a major consequence of climate change and ocean acidification, which are both becoming more and more prevalent in our world today. As water temperatures increase, corals will expel the zooxanthellae living in their tissues, and thus coral bleaching occurs. As the Earth’s climate changes toward warmer air temperatures, the temperature of the ocean increases as well. Scientists have predicted and feared the consequences of climate change and the effect it would have on coral reefs for some time (GBRPA). Temperature increases as small as one degree Celsius for up to only four weeks can trigger a coral bleaching event. If such temperatures persist for eight weeks or more, corals will begin to die off, not only regionally but globally as well (GBRPA). Other causes of coral bleaching include low salinity and decreases in water quality due to contaminated run-off. Both of these factors are dependent upon weather and climate as well.
This Year’s Effects
This year’s El Niño weather pattern is no doubt playing a part in the considerable increase in coral bleaching, not only on the Great Barrier reef but on reefs in Fiji and Hawaii as well (McKirdy). An El Niño is characterized by warmer than usual climate patterns, which raises ocean temperatures as well, especially in the Pacific Ocean. El Niño years are known for their in creasing effects on coral bleaching in the Pacific region reefs, and can sometimes be devastating (McKirdy). This climate change is definitely playing a major factor in the bleaching that continues to plague the Great Barrier Reef of Australia.
“Managing the Reef: Coral Bleaching.” Australian Government: Great Barrier Reef Park Authority. Australian Government Great Barrier Reef Park Authority (GBRPA), 2002.
McKirdy, Euan. “Study: 93% of Great Barrier Reef Bleached.” CNN. Cable News Network, 20 Apr. 2016.