In 1998, 16% of the hard corals in the world died. That’s right, almost a fifth of all the coral in the world knocked out in a single year, and most people have never even heard about it. The cause of this widespread death of corals was that 1998 was the hottest year on record for oceans (both for the records kept since 1860, and the records going back 800,000 years through ice core data). In 1998, sea surface temperatures rose by 1-3 Deg. Celsius, and the first recorded global bleaching event occurred.
But, 1998 wasn’t able to hold onto its record for long, as 2002, 2010, and 2014 soon stole the record for hottest year. In all of those years, mass coral bleaching was experienced in many sites around the globe, however not as many corals died. Mostly because there are not as many corals now as there was before 1998, and also that the corals left are the more heat-tolerant species (with the less heat tolerant species now gone from many areas). Now, in 2015, the US National Center for Oceanic and Atmospheric Sciences (NOAA) is predicting that an El Nino event coupled with higher temperatures from decades of climate change will result in the planets third global bleaching event (Read the Full Report Here). Already by early March, bleaching is being reported in many areas of the Southern Hemisphere, and reports from American Samoa have stated that the corals there are 100% bleached. Between March and June, those warmer than average temperatures will reach the Northern Hemisphere, and reef scientists can only wait and watch to see what will happen.
Coral bleaching is a process in which the normal symbiosis between corals and single-celled algae which live inside their bodies starts to break down. This can be caused by different problems, but the major one here is due to higher temperatures, generally a few degrees above average. Like us, corals have a narrow range of temperatures in which they are able to survive. We have evolved very sophisticated and complex ways to regulate hot and cold, but a change in our core temperature of only 2 degrees up or down can result in major problems or even death. Corals have none of the adaptations to regulate hot and cold like we do, so when the temperatures rise by a few degrees there is nothing they can do to protect themselves. They lose the algae inside their body, which supply 85-95% of the coral’s energy budget, and are left to survive on just their reserved fats and oils. If the corals don’t have much reserves they will perish quickly, but the ‘fat’ corals can survive longer. In this stressed state, any other problems such as sedimentation, algae overgrowth, disease, predators, etc. can easily kill the corals (see our article “What is Coral Bleaching” for more information).
Due to climate change, coral reef scientists have been predicting for decades that most coral reefs in the world will be lost. With many claiming that the upper threshold of CO2 concentration in the atmosphere for corals to survive is 350ppm, coral reef scientists are no longer optimistic people (today the concentration is over 400ppm, as you can read about in this article). In the past few decades we have been constantly setting records, making history, and having to rewrite the rules for reefs; but not in ways we can be proud of. Prior to 1979, the term ‘Mass Coral Bleaching’ did not exist. The first time humans witnessed such an event was in 1979-1980 on the Great Barrier Reef. Since that year, Mass Coral Bleaching events have been experienced in every single coral reef region in the world, in every decade. Then, in 1998, the first global bleaching event was witnessed, but most thought that was an event that would occur only once every few hundred years. Since then, we have broken the record 3 times, and set to break it a fourth time this year.
If this article is starting to seem a bit dark and pessimistic, that’s because it is. Unfortunately, coral reefs around the world are under threat. They are the fastest declining ecosystems, and have been for decades. Over 90% of the corals in the Caribbean are already gone, and over 50% of the corals on the Great Barrier Reef have already been lost. Nowhere in the world are coral reefs doing better than they were in the last century, and in terms of coral lost per decade this is the fastest extinction event the reefs have ever faced in their 250 million year history.
There is not much we can do to control the effects of climate change, the topic has been with leading world governments and the UN since the 1960’s and still nothing substantial has been done. But, there are plenty of things we can do to reduce the other threats reefs face so that less corals are loss during bleaching events, and maybe a few will be able to acclimatize and adapt to bleaching events if given enough time. Great things are being done on the ground in many areas, run mostly by local communities and reef managers. You can find out more about our projects and activities on our main conservation page, but no matter where you live you should be concerned about this problem. The coral reefs of the world are the oldest and most biodiverse ecosystems. In addition to providing food and protecting shorelines, reefs are responsible for much of the atmospheric gas and nutrient regulation on our planet. Our health is completely dependent upon theirs.
Find out more about this topic on the NOAA Coral Watch Website, where you can view real time temperature data for the entire planet.
You can also check out some of our other articles on this topic, by following the links at the bottom of this post.