Today we completed three survey dives on Lighthouse Reef. On one dive, we spotted a boulder of monstrous coral suffering from black-band disease. Black-band disease is characterized by a blackish crescent-shaped band, 1 to 30 mm wide and up to 2 m long, it “consumes” live coral tissue as it passes over the coral surface, leaving behind a bare white skeleton. More here: http://www.coris.noaa.gov/about/diseases/
In an earlier blog post, we discussed the devastation that white-band disease caused Acropora coral in the Caribbean region thirty years ago. It was on this expedition, at Glover’s Reef in July, that we noticed possible signs of recovery.
Coral disease is a Caribbean-wide problem. Until the early 1990s, there were only a few known coral diseases: White-band disease, black-band disease and white plague. However, from the mid 1990’s, the number of diseases escalated and today, some form of coral disease is known to infect most of the reef building corals in the Caribbean.
Coral diseases can be caused by infection from bacteria, fungi or viruses, and/or coral stress caused by warmer seawater temperatures, ultraviolet radiation, excess sediment or pollution. One type of stress may work to exacerbate the other (Santavy and Peters, 1997).
Corals have a number of defense mechanisms to fight against disease including being able to secrete a mucous-rich biofilm which coats the coral’s outer tissues in natural ‘protective’ bacteria. However, when corals are stressed, they secrete extra mucous, which leads to elevated levels of natural bacteria, as well as the introduction of new, potentially harmful bacterial populations.
With the rapid spread of coral disease across the vast Caribbean region, many scientists believe that deteriorating water quality associated with pollution and increased sea surface temperatures have caused corals to lose the ability to protect themselves against disease. Corals simply cannot cope.
Through the expansion of reef monitoring programs, improved laboratory techniques to investigate disease development and good management to minimize human-related factors contributing to the spread of coral disease, we may be able to better understand (and protect against) coral disease.