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Scientists sound alarm over disease wiping out Caribbean coral

A deadly disease is killing coral in the Mexican Caribbean at a rapid rate and new research shows the outbreak probably can't be stopped without human intervention.

(CN) — An outbreak of a disease that has killed up to 94% of some coral species in the Mexican Caribbean highlights the need for human interventions to prevent extinction, researchers say.

The extremely contagious and fast-spreading stony coral tissue loss disease, or SCTLD, was first reported in South Florida in 2014 and has since spread across the Caribbean, in some instances killing infected coral within weeks, according to a study published Thursday in the journal Communications Biology. The disease is likely one of the deadliest to ever affect coral.

Lead researcher Lorenzo Álvarez-Filip and his colleagues surveyed 35 Caribbean Sea sites during 2016 and 2017, before SCTLD had reached the region, and 101 sites after the disease appeared, from July 2018 and January 2020. Their findings are dire.

Of the 29,095 coral colonies surveyed after the Mexican Caribbean outbreak, 17% were already dead, with an additional 10% affected by the disease. Across 48 species surveyed, the death rate among the 21 species affected by the disease ranged from less than 10% to up to 94%.

The Caribbean region is a known hot spot for diseases, some of which have decimated the populations of primary reef-builders, resulting in devastating changes to the reef environment, according to the study. The article points out that disease outbreaks are often associated with mass mortality events and can rapidly and drastically reduce populations over a short period of time.

“When these events affect foundation species, population losses result in changes in the local environment, upon which a variety of other species depend, and altering the structure and functioning of the entire ecosystem,” the article says.

Since the health of coral reefs are closely tied to human-induced factors – such as rising sea temperatures, decreased water quality and nutrient enrichment – there is an ever-increasing risk of diseases that could impact the stability of reef ecosystems.

The researchers found that species belonging to the reef-building maze and brain coral groups were the most seriously affected, with maze coral species and the pillar coral known as Dendrogyra cylindrus exhibiting population losses greater than 80%.   

Aside from population losses caused by SCTLD, researchers observed a 30% reduction in the ability of coral communities to produce calcium carbonate, the material required to make the complex three-dimensional structures of coral reefs. This impairment could lead to reef frameworks being destroyed faster than they are produced.

“This emergent disease is likely to become the most lethal disturbance ever recorded in the Caribbean,” the authors wrote.

The full consequences of this widespread disease are yet to be known.

Many of the afflicted species are slow growing, and the replacement of dead corals will take decades to replenish, the researchers warn.

Unfortunately, the study found there is a great likelihood that microalgae cover will rapidly overtake the free space left by dead corals, hindering coral recovery.

Natural restoration processes will probably be insufficient to restore the severe population losses, the article says, meaning human intervention to rescue colonies of vulnerable species and preserve their genetic material is likely the only way to facilitate recovery and prevent the region-wide extinction of some species.  

“We believe, however, that these actions will only succeed if they are accompanied by stringent controls that take into consideration climate change, coastal development, and wastewater treatment to improve local conditions and ecosystem resilience,” the researchers concluded.

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