An Update on the State of the World’s Coral Reefs
Coral reefs are one of our most loved and magnificent ecosystems, not to mention one of the most unique and biodiverse on the planet. Yet these incredible habitats are highly vulnerable in the face of climate change as they struggle to adapt to warming seas and ocean acidification. Let’s take a closer look at the current state of our world’s coral reefs to understand better if they have a chance of surviving the new environment we are creating.
Corals in the Caribbean are currently suffering from a highly contagious epidemic which is seeing disease spread rapidly through coral colonies. Stony coral tissue loss disease (SCTLD) was first discovered in Florida in 2014 and is thought to have arrived in the area after travelling via ocean currents and the increasing number of ships. In the last eight years, this disease has spread throughout the area at a worry rate of one mile a month and now affects the reefs surrounding 22 Caribbean countries. SCTLD attacks 30 species of coral, including some of our biggest and most important for reef building which can take centuries to grow. Local scientists have seen healthy colourful reef systems transform to monochrome graveyards as the disease eats away corals’ soft tissue until only their skeleton remains. Once the living tissue has disappeared, algae move in and cover the area in a dull green or reddish brown fuzz and buzzing reefs can be transformed to dark ghostly areas in only a matter of months.
Scientists are working hard to understand this disease but so far, they have been unable to pinpoint the pathogen which is wreaking havoc in the area. At present, the only treatment they have been able to devise is to apply antibiotic paste on individual corals, a process which has seen a 70% success rate in Puerto Rico. However, this method of treatment is both time consuming and expensive, with both the Coronavirus pandemic and a lack of funding slowing down essential work. For example, in the Bahamas, scientists were forced to lose precious time as they waited for the government to issue permits which allowed them both to study and treat the disease. After a long wait, conservationists finally became frustrated and broadcast their dilemma to the public which helped speed up the permit process. However, their resulting permit only lasted three months after which time, they would have to go through the process again. It seems that bureaucracy is failing to keep up with the pace of SCTLD, yet some countries are reluctant to treat the disease at all. In the Dominican Republic, the use of antibiotics in the open ocean is banned due to the uncertain effects they have on the marine environment in the long term, such as causing antibiotic resistance and impacting essential bacteria; but which is worse, increasing antibiotic resistance or watching our corals die? Others believe that treatment of SCTLD is the wrong approach altogether and choose to focus on the survivors that have managed to resist the wrath of the disease as these are our strongest and most resistant colonies which are most likely to survive future stressors. Controversy remains around how we should tackle this problem, yet most agree that we will be unable to save all our reefs, we instead must target priority areas with large, older corals and hope that the reefs will be able to build themselves back up from there.
The prevalence and impact that this disease has had in the region has led to some arguing that we should have emergency reserve funds in place ready for devastating events such as this. For not only are corals important in biological terms but they are also incredibly important for the economy, providing the base of some countries’ tourism industry whilst being the very foundations of multi-million dollar fishing industries. In fact, to protect against the loss of future corals, coral banks are now being created so that we can preserve a diverse range of genes, meaning our coral species may not be lost forever under unfavourable conditions. These specimens are being cultivated in labs and cross bred with each other in the hope that scientists can develop a new strain which is highly resistant to both disease and warming seas which one day might be used to repopulate areas of ocean where reefs have disappeared.
Sadly, corals on the other side of the world in Western Australia are struggling too. A coral bommie, estimated to be 1,000 years old, residing off the Ningaloo coast is thought to have died as it has recently turned white. The four metre structure, locally nicknamed Ayers Rock, is now being taken over by brown algae yet, for once, rising temperatures are not to blame but a spawning event gone wrong. Each year, a giant spawning event takes place which sees corals release sperm and eggs into the water where they can fuse together to create new coral larvae. However, in March this year, the weather didn’t quite play ball as Cyclone Charlotte and a following low pressure system trapped the newly formed larvae in the bay, rather than allowing them to disperse in the open ocean. This led to the spawn decaying in the bay and in the process, created an oxygen-starved dead zone which killed both local corals and fish in a four kilometre stretch of the nearshore waters. Whilst this isn’t the first time this has occurred, locals say it is the worst they can remember for decades and believe it could take up to 20 years for the region to fully recover.
On Australia’s opposite coast, the Great Barrier Reef has just been confirmed to have suffered its sixth mass coral bleaching event which sees hot, stressed corals expel the algae that live within them, meaning they lose both their source of nutrients and their colour, leading to white ‘bleached’ reefs. Aerial surveys show that 1,200 kilometres of the famous reef have been affected in the fourth bleaching event since 2016. Up until this point, scientists believed that cooler La Nina years would allow reefs the chance to recover from warming waters, however this latest event has occurred during this cooler period, meaning our reefs could struggle to bounce back as they have before. However, the aerial surveys showed that whilst some areas of the reef were badly bleached, others showed very little signs of bleaching whilst some looked as healthy as ever, providing a small chink of light in amongst their gloomy findings.
On a more positive note, promising news has been coming from East Africa, specifically Kenya and Tanzania. Local conservationists believe that they have found a climate refuge for corals; a patch of cooler ocean waters where reefs and their inhabitants are thriving despite surrounding warming seas. In fact, the area contains spinner dolphins, dugongs and prehistoric fish! Why is the water here so cool? Its all thanks to Kilimanjaro and the Usambara Mountains which feed this area of ocean with cold glacial water through deep channels which formed thousands of years ago. The protected refuge area is 150 square miles and conservationists are now researching other promising areas in the Indian Ocean which could provide sanctuaries against the rising heat. The biggest challenge here now is ensuring that no other human impacts threaten the thriving marine life and ‘happy corals’ in the area.
Other research conducted in the Indian Ocean has shown that recovery from bleaching events can be surprisingly quick so long as the conditions are favourable. For example, in the Chagos Islands, positive growth of the reef was seen only six years after a bleaching event because key species returned to the area quickly and because the underlying structures remain undamaged. This type of recovery is only possible however, if our reefs get a break from extreme warm weather events, an increasingly unlikely scenario on our current climate trajectory.
Yet it’s not time to despair just yet as studies in Hawaii have recently shown that corals are a lot more resistant to a changing climate than we think. Scientists grew different species of coral in a lab under the temperatures and acidity levels which we are expected to experience in the future. Some of each species did die but none completely died off and in fact, some even thrived under the new conditions! This is believed to be one of our most accurate studies yet as the corals were given 22 months to adapt, rather than around six months as in previous experiments. Some parts of corals take a long time to adjust and whilst there was a dip in their health initially under the new stressors, in the longer term they were able to recalibrate and return to a normal state, although of course they were not also battling with other issues, such as pollution, in the laboratory tank.
Whilst there is definitely a fair share of worrying and alarming news stories out there regarding our reefs, there are also a few glimmers of hope that these plucky creatures are a lot more hardy than we realise. Our natural world is always throwing us surprises, such as the recently discovered three kilometre pristine reef off the coast of Tahiti or the increasingly noisy reefs hugging the coast of Indonesia as fish return with whoops and growls to healthy ecosystems. The future isn’t definite but it’s certainly not time for us to lose hope for our corals just yet.
By Neve McCracken-Heywood