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Coral

Can Firefighting Strategies Save the Corals?

The article: Randall, C.J., E.M. Whitcher, T. Code, C. Pollock, I. Lundgren, Z. Hillis-Starr, E. Muller. 2018. Testing methods to mitigate Caribbean yellow-band disease on Orbicella faveolata. PeerJ, 6:e4800. https://doi.org/10.7717/peerj.4800

 

Firebreaks, natural or manmade, are obstacles used to reduce the spread of terrestrial fires. But what happens when the “fire” is underwater? Randall et al. (2018) draw analogies between the techniques used to mitigate severe and widespread coral diseases and those used to reduce raging forest fires.

Figure 1.Caribbean yellow-band disease on Orbicella faveolata. Source: C.J. Randall

What is Caribbean Yellow-Band Disease?

Worldwide, coral reefs comprise 1% of the Earth’s surface and provide an estimated $375 billion in goods and services annually. Their beneficial goods and services and ultimate survival, however, are threatened by pollution, overfishing, ocean acidification, and disease. One specific disease called Caribbean yellow-band disease (CYBD) is raging in the West Indies, causing slow-moving lesions that typically result in loss of coral tissue. In addition to the overall mass of the coral colony being reduced, the reproductive output (production of offspring over the individual’s lifetime) is obstructed. The thing is, scientists do not know all too much about what causes CYBD. While researchers work to determine the causes of yellow-band disease, effort is also going towards testing mitigation efforts to minimize the spread of disease.

Can we help defeat the yellow-band?

Buck Island Reef National Monument, a long-term CYBD monitoring site for mountainous star coral Orbicella faveolata (Figure 1), was optimal for testing the application of various disease mitigation techniques: (1) aspirating, (2) shading and (3) chiseling (firebreaks).

Disease-Mitigation Techniques:

Aspirating

Perhaps the most intuitive approach is to mechanically remove the diseased tissue. Through a powerful siphon, the researchers attempted to aspirate the diseased tissue from the affected colony, collecting the tissue at the water’s surface (Figure 2a). Despite the aggressive aspiration, the researchers noted that bits of tissue still remained in crevasses of the coral skeleton.

Shading

Scleractinian (stony) corals, comprised of coral polyps, algae, and bacteria, depend on light to induce photosynthesis. It is thought that CYBD is an infection of the corals’ photosynthetic cells that leads to the buildup of reactive oxygen species from an overexposure to light, which may compromise corals’ immune-competence. Randall et al. (2018) attempted to impede the activity of photosymbionts in the coral tissue (Figure 2b). By reducing the UV light reaching the disease lesions in O. faveolata with shade cloths, the researchers may improve the corals’ ability to battle CYBD.

Chiseling (Firebreaks)

The third approach resembled a firebreak. By creating a physical barrier between the diseased and healthy tissue using a chisel, Randall et al. attempted to isolate the pathogenic microorganisms (Figure 2c) just as a river would barricade a powerful forest fire.

Figure 2: CYBD mitigation techniques. (A) Shading, (B) Aspiration, (C) Chiseling. Source: C.J. Randall

So what can we do?

After seven months of testing these techniques on nine O. faveolata colonies, Randall et al. (2018) found that neither aspiration nor shading significantly reduced the spread of yellow-band disease. The firebreaks, however, prevented the disease from spreading to the healthy tissue. So should we start employing underwater “firefighters” to combat this voracious disease? Are firebreaks currently our best tool for tackling yellow-band disease?

Randall et al. (2018) scaled up the chiseling experiment and determined that the firebreaks can reduce the rate of tissue loss by 29%. The effectiveness of chiseling varied with seasonality, wound width, placement, and epoxy application. At its current stage of development, the firebreak technique is therefore not the recommended mitigation technique. As with many coral diseases, when we learn more about the cause of disease, we can refine techniques like firebreaks to make them more effective. By determining how to help corals fight disease and saving our coral reefs, we can strengthen our fisheries, shoreline protection, and overall quality of life.

 

 

 

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