The world’s coral reefs have gone through the worst mass bleaching events over the past several years. They are extremely sensitive to ocean temperatures. Thus, when the temperature rises just a couple of degrees, corals turn white as it sheds the algae it relies on for survival. While bleaching does not kill the coral, it does weaken them and makes them vulnerable to disease.
Scientists predict that the world’s coral reefs may be lost to the climate crisis by 2100. Forecasts show that about 70% to 90% of them may disappear in the next two decades mainly due to rising sea temperatures, acidic water, and pollution. "By 2100, it's looking quite grim," Renee Setter, a biogeographer at the University of Hawaii Manoa, said in a statement.
The researchers said that while pollution poses a large threat to many ocean creatures, corals seem most at risk from emissions. "Trying to clean up the beaches is great and trying to combat pollution is fantastic. We need to continue those efforts. But at the end of the day, fighting climate change is really what we need to be advocating for in order to protect corals and avoid compounded stressors,” Setter added.
Unfortunately, coral reefs are dying off not only because of climate change but because of a mystery disease.
The Stony Coral Tissue Loss Disease
In 2014, scientists noticed big white lesions eating into the colorful tissues of hundreds of stony corals in Florida. Since then, it has reached several Caribbean sites, causing major mortality in multiple species of reef-building corals. The disease is currently ravaging Florida’s stony corals, which is considered the third-largest coral barrier reef in the world. Thus, scientists are worried and are working quickly to understand it better.
"It's really sad. Some of these corals that have been growing for tens to hundreds to possibly thousands of years are disappearing in months. We're talking about corals that have literally built this reef now dying, and it's pretty scary that something we can't yet identify is destroying everything,” Allan Anderson, a coral caretaker at Florida Fish and Wildlife Conservation Commission (FWC), said.
While the “mystery killer” has been identified as the “Stony Coral Tissue Loss Disease” (SCTLD), its exact pathogen still remains unidentified. According to EcoWatch, a leading environmental news site engaging millions of concerned individuals every month, SCTLD can kill an entire coral colony, infect many different coral species, and linger for a long period. These factors made scientists realize that the disease is different and more devasting than other coral diseases.
"Corals affected by SCTLD lose tissue really fast. Unlike many other coral diseases that can take weeks or months to pass over a coral's surface, SCTLD can kill a colony within a few days under 'ideal circumstances.' Some species, principally the brain corals, have almost disappeared from local reefs within a period of about six months,” Andrew Baker, professor at the University of Miami Rosenstiel School of Marine Science, said.
A recent study published in Frontiers in Marine Science revealed that SCTLD can form hotspots of more than 140 kilometers at once. It is more prevalent in deeper reefs with more diverse coral species and spreads at an unfortunately persistent pace regardless of changing temperature and nutrients. The findings also showed intriguing possibilities. According to Mote.org, one of the oldest marine research laboratories in Florida, the researchers suggested that the bottom-water currents and sediments could play bigger roles in the disease spread than previously realized.
What Measures Are Being Taken
Rob Ruzicka, the Coral Reef Research Program manager at the Fish and Wildlife Research Institute (FWRI), said that they have never seen a disease outbreak affect this many species at one time. In Florida, for instance, nearly half of the coral species have developed lesions and died with it. Another characteristic of this disease event that’s very unfortunate is how rapid the lesions occur. Also, there’s a low chance that the corals survive this disease.
Fortunately, many scientists and organizations are working to address this problem. The decisions of the 10th Meeting of the Contracting Parties (COP) of the SPAW Protocol and the 15th COP of the Cartagena Convention Secretariat, both held in Roátan, Honduras last June 2019, provided capacity-building support to areas affected or susceptible to transmission of SCTLD.
Scientists at Mote’s Elizabeth Moore International Center for Coral Reef Research & Restoration (IC2R3) in Summerland Key, Florida, are also still working to understand and address SCTLD and help reefs recover through science-based coral restoration. “This is the first publication providing a perspective of stony coral tissue loss disease over the entire Florida Reef Tract on a large-scale and multi-year timescale,” the study’s first author, Dr. Erinn Muller, Science Director of Mote’s IC2R3, said.
According to Science News, an online site that features daily news articles, feature stories, reviews, and more in all disciplines of science, many scientists are trying to save Florida’s reef-building corals by moving hundreds of healthy colonies to tanks, where they can be studied, bred and protected from the outbreak along the coast. Karen Neely, a marine biologist at Nova Southeastern University in Fort Lauderdale, estimates that Florida researchers treated nearly 1,200 colonies last January 2019.
The FWC Coral Rescue Team is also identifying, collecting, measuring, and sampling corals susceptible to SCTLD that would likely perish if left on the reef. "The rescue mission is exactly what it sounds like. We're trying to collect these corals and take them out of their natural environment before they get hit with this disease. Most of the individuals we're collecting would have been affected and dead within X amount of period, depending on the species, so we're definitely at that last stage. We do need to collect these corals,” FWC Coral Program research assistant Ananda Ellis said.
Currently, the researchers have collected nearly 2,000 individual corals from 22 target species. Stephanie Schopmeyer, a main FWC coordinator for the rescue cruises, said that they had enough unique genotypes of each species through genetic sampling to preserve genetic diversity during the next phase of the rescue mission: coral propagation for future restoration activities.
"Over time, we should be able to breed or propagate or grow enough coral to repopulate the entire reef tract. That is the actual goal,” Schopmeyer said.