Deadly and Fast-Moving Coral Disease in Caribbean Linked to Wastewater From Ships

According to studies, a deadly and fast-moving coral disease that ravaged the Caribbean might be related to waste or ballast water from ships.

SCTLD

The fatal illness, known as stony coral tissue loss disease (SCTLD), was discovered in Florida in 2014 and has since spread across the area, giving experts great alarm.

It spreads quicker than other coral diseases and has an exceptionally high mortality rate among the species most vulnerable to it, perhaps making it the most lethal disease ever to strike corals. More than 30 coral species are vulnerable. It was first discovered in Jamaica in 2018, then spread to the Mexican Caribbean, Sint Maarten, and the Bahamas, before being found in 18 more nations.

In one research in Mexico, more than 40% of reefs had at least 10% of coral infected with SCTLD, and nearly a quarter had more than 30%. In Florida, regional coral density losses were as high as 30%, while living tissue loss was as high as 60%.

Ballast Water

A new study suggests ship ballast water may be to blame for SCTLD. However, scientists have yet to identify whether the illness is caused by a virus, bacterium, chemical, or another infectious agent. The study was published in the journal Frontiers in Marine Science.

"The prevalent currents in the Caribbean drive saltwater to Florida rather than the other way around, and the primary wind direction is westward," said Judith Lang, scientific director of the Atlantic and Gulf Rapid Reef Assessment project, which has been following the illness. As a result, human dispersal [to those three territories] appears to be essential in 2018."

The International Maritime Organization implemented the Ballast Water Management Convention in 2017 in response to the spread of deadly pathogens by ships when they discharge ballast water. The convention requires ships to release their ballast water - which is used to maintain the ship's stability - 200 nautical miles from shore in water at least 200 meters deep before entering port to ensure they do not bring in pathogens.

Related Article: Storm Ridden Coral System Restored by a Radical 10-Year Restoration Project

Rapid Spread

SCTLD has grown fast in the Bahamas after its discovery in December 2019.

"The illness is distributed throughout around 75km of reef tract, about 46 miles - so for Grand Bahama, it is a huge structure of the reef," said Krista Sherman, senior scientist at the Perry Institute and a co-author of the published article. So we're talking about essentially covering the whole island's southern coastline."

The illness is also common in the coral reefs of New Providence, which is home to Nassau, the Bahamas' capital and main port. According to the research, there are international cargo ships, cruise ships, and pleasure boats in that area and a gasoline shipping station.

Infection Rates

Infection rates among the most vulnerable species were 23% and 45% in New Providence and Grand Bahama, respectively, while current death rates have reached almost 43%.

The researchers discovered that, except for two species, "there was a strong relationship" between the disease and the proximity of reefs to major shipping ports. "On both islands, an increasing proportion of healthy colonies as the distance from the port rose, and a larger proportion of recently dead colonies closer to the port than farther away," they observed.

According to Adrian LaRoda, head of the Bahamas Commercial Fishers Alliance, there are worries that the coral disease may harm the country's major fisheries export, spiny lobster. Although lobster fishermen labor further out to sea, the industry would be broken if the reefs perished. The spiny lobster fishery generates $90 million (£66 million) annually and employs 9,000 people.

"Any bad influence on our reefs will undoubtedly have a significant impact on our spiny lobsters since adult animals move [from the reefs] to fish aggregating devices [a method of collecting fish]," LaRoda explained. In addition, he said that the lobsters' reproductive rate and the food availability for immature lobsters on the reef will be impacted.

Government Action

To address the issue, the Bahamas' government has formed a national task force. The most effective therapy for the disease is applying antibiotic amoxicillin directly to the corals, which has had some effectiveness in lowering mortality, but there is no viable long-term cure.

Rather than addressing the symptoms, Lang believes it is necessary to address the probable human-caused causes. "Given a chance, nature can repair itself," she added.

Also Read: UNESCO: Great Barrier Reef Should Be Classified as "In Danger" Due to Degradation

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