Coral disease is pushing Caribbean reefs toward extinction

The health of Caribbean reefs is under threat from a virulent disease known as stony coral tissue loss disease (SCTLD). Initially reported near Miami in 2014, this disease has since affected coral populations across 18 countries and territories in the region.

Stony coral tissue loss disease devastates coral colonies, leaving behind barren skeletons where vibrant life once thrived.

Transforming Caribbean reefs

A recent study has shed light on the profound shifts occurring within the reef ecosystems due to SCTLD. The disappearance of susceptible coral species is paving the way for more opportunistic organisms – such as macroalgae, cyanobacteria, and fire coral – to dominate.

These “weedy” species, thriving in the absence of their traditional coral competitors, create a landscape vastly different from the once calcified structures of coral reefs.

The ripple effects of these changes are significant. Coral reefs, once bustling with diverse marine life, are transforming into environments dominated by seaweed.

While this new setting benefits certain herbivores, it fails to provide the complex habitat structure needed by other marine species for activities such as hiding, mating, and growing.

Broad ecological changes

“In less than 10 years, a deadly infectious agent called stony coral tissue loss disease (SCTLD) has emerged as a leading threat to Caribbean coral reefs,” wrote the study authors.

“Although its etiology is not fully understood, the discovery of bacterial disease indicators and the success of probiotic treatments suggest that bacteria are involved.” 

“Other evidence suggests that SCTLD is caused by a virus that attacks some corals’ endosymbiotic algae, but not others. SCTLD has reduced coral cover by 30 to 60% in affected regions, pushing a few coral species toward local extinction.”

“Because diseases are most likely to have indirect community effects when they affect connected, unique, or widespread host species, we hypothesized that SCTLD-caused coral loss could trigger broad changes in diverse coral reef ecosystems.”

Long-lasting consequences

Sara Swaminathan, the lead author and a PhD candidate in Environmental Engineering Sciences at the University of Florida, explained the critical implications of these changes. “While some fast-growing organisms might initially thrive, the broader ecological balance is tipped, potentially leading to long-lasting repercussions,” she noted.

Further studies involving data from various U.S. territories, including Florida, Puerto Rico, and the U.S. Virgin Islands, have highlighted additional consequences.

For instance, the disease impacts crustose coralline algae, vital for reef building, thereby inhibiting the structural integrity and resilience of the reefs themselves.

Fish and their changing habitats

The research team also discovered that the impact of the coral disease on fish populations is nuanced. Some fish species find new advantages in the altered environments, while others suffer due to the loss of their habitats.

The roughness of the coral, or rugosity, now plays a more significant role in determining the suitability of these habitats for different fish species, regardless of whether the coral is alive.

Kevin Lafferty, a senior scientist with the U.S. Geological Survey, highlighted the complexity of SCTLD’s impact. “Some infectious diseases reshape entire ecosystems, and SCTLD is a prime example, creating a mix of winners and losers among marine species,” he remarked.

Collaborative efforts to preserve Caribbean reefs

The international community, including marine biologists and conservationists, has rallied to address this crisis. Efforts to understand the mechanisms behind the disease and develop potential treatments are ongoing. Promising approaches like the application of probiotics to affected corals show potential in mitigating the disease’s progression.

Andrew Altieri, an assistant professor and associate director at the Center for Coastal Solutions, emphasized the broader implications of coral loss. “Coral reefs are not just biodiversity hotspots; they are crucial for the survival of numerous marine species and for the protection of coastal economies relying on fishing and tourism,” he stated.

The collective efforts of researchers and conservationists are crucial in preserving these vital ecosystems.

As the battle against stony coral tissue loss disease continues, the commitment to understanding and combating this disease remains paramount, not only for the health of the coral reefs but for the countless human and marine lives that depend on them.

The study is published in the journal Science Advances.

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