Living among the sessile or attached corals are more than 100 species of jellyfish 3,000 species of mollusks 500 species of worms 1,625 species of fish including 133 types of sharks and rays and more than 30 species of dolphins and whales 5 Six of the world’s seven sea turtle species visit the GBR Raine Island in the GBR is the world’s largest breeding site for green turtles At least 242 bird species visit the GBR many of them breeding on the cays and islands 6 The teeming brightly colored life of the coral reef is more diverse than any ecosystem on Earth except the tropical rain forest But the Great Barrier Reef is changing rapidly THE GBR AND CLIMATE CHANGE The major threat to the Great Barrier Reef is climate change a complex process with multiple effects Two effects are especially dangerous to the reef rising temperatures and increasing acidity in the ocean The most visible impact is coral bleaching or whitening caused by high temperatures which puts stress on corals Temperature-stressed corals expel their THE GBR FROM SPACE Reefs along the GBR reach upward from the shallow seafloor The skeletons within the reefs are interconnected by their calcium carbonate structures Corals form most of the reef but trillions of tiny pink coralline algae also secrete calcium carbonate and help cement the reef together This true-color image of the GBR taken by NASA’s Terra satellite on August 26 2000 shows part of the central portion of the reef near the Queensland coast zooxanthellae the tiny algae that live inside their tissues Zooxanthellae keep the corals alive their photosynthesis produces most of the corals food Corals can recover from short periods of increased temperatures but if the heat continues they die An increase of only 8
1 8 to 2 7 degrees Fahrenheit 1 0 to 1 5 C for six weeks results in extensive coral bleaching followed by death unless reef temperatures quickly return to normal 7 Since 1979 the GBR has experienced eight mass bleaching WHAT IS BIODIVERSITY Biodiversity or biological diversity refers to the variety of living organisms in an ecosystem Biodiversity encompasses variety in the species present the genes they contain and the ecosystems they live in The GBR is biodiverse in all of these ways Biodiversity is essential ecologically because it helps stabilize an ecosystem Biodiverse ecosystems are productive healthy self-sufficient and better able to overcome disasters If part of an ecosystem sickens or dies high biodiversity allows the rest to survive and restore the system events as a result of increasing temperatures Two very bad years were 1998 and 2002 During those two years 42 and 54 percent of the reefs respectively were bleached Then during the years 2015 2016 the most extreme bleaching event ever recorded on the GBR occurred Researchers reported that 93 percent of the reefs especially those in the northern region suffered from some level of bleaching 8 All of these bleaching events were associated with an El Niño event a periodic weather pattern that brings warmer-than-average water to the Pacific Ocean When combined with global warming El Niño events result in major bleaching during that year or the next The 1997 1998 El Niño was the strongest in recorded history and the 2015 2016 event was a close second The 2002 weather pattern was moderately strong If the water cools sufficiently reefs may rebound but many corals especially old slow-growing ones take decades to recover In early 2016 divers near Cape York at the reef’s northeastern tip discovered that half of the corals had already died and a full 75 percent in the reef’s northern half were damaged 9 Over the hot still summer the reefs 9
were bathed in extremely warm water for months This area of the reef had been considered its most pristine and the 2016 bleaching event was the worst ever recorded at the site Most of the southern reefs remained largely intact due to heavy rain and cloud cover during the summer Climate change damage does not stop with bleaching Climate change results primarily from fossil fuel burning which raises temperatures in the atmosphere by releasing greenhouse gases The most plentiful greenhouse gas in the atmosphere is carbon dioxide CO2 When carbon dioxide dissolves in the ocean it reacts with water to become carbonic acid which makes water more acidic Corals are affected by acidification because of their calcium carbonate skeletons Already existing coral skeletons may be corroded by the acid The new coral growth may be slowed resulting in weaker reefs that are more likely to erode Recent studies show that some coral species may be able to control their internal acidity and cope with increasing levels of acid in the water But studies indicate future acidification may damage the GBR 10 DOCUMENTING DEATH Diver Richard Vevers was most disturbed by the smell When we got back on the boat we realized we just stank stank of the smell of rotting animals Vevers is chief executive of the Ocean Agency an organization he founded to bring attention to environmental problems He photographed Lizard Island reef which was affected by the 2016 GBR bleaching event He took pictures of the reef before bleaching began just after bleaching started and finally weeks later when its effects became obvious The healthy reef was luxuriant with life The dying reef was brilliant white deceptively beautiful But several weeks later Vevers said It was one of the most disgusting sights I’ve ever seen 10 Hard corals were blanketed by algae and seaweed Soft corals were decomposing their flesh dripping off the reef structure Other animals had disappeared The reef was no longer diverse and colorful Its corals were all dead
OTHER IMPACTS The GBR is threatened by more than climate change It is damaged by shore-based pollution including toxic chemicals from industry and nutrient runoff from agriculture and sewage Excess nutrients speed up algal growth blocking sunlight and causing algae to overgrow the reefs In addition some people cause direct damage to reefs They drop anchors or carry out dredging and trawling breaking off pieces of the reef structure They use unsustainable and destructive fishing methods The single biggest thing we can do to protect the Reef for the future is to greatly reduce greenhouse gas emissions as soon as possible 11 David Wachenfeld director of reef recovery at the Great Barrier Reef Marine Park Authority Finally similar to marine organisms throughout the oceans residents of the GBR are succumbing to plastic pollution Polyps are filter feeders They draw into their bodies whatever is present in the water passing over them This includes microplastics tiny beads of plastic ground down by waves until they are small enough to become coral food But corals cannot break down plastic which remains in their digestive systems and may prevent them from digesting real food When corals eat microplastics they can starve THE FUTURE OF THE GBR Research released in 2016 suggests the GBR may be in even more danger from climate change than previously suspected Temperature spikes are known to kill corals but temperature changes are not uniform across the reef When part of the reef receives a 11
