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- Importance of Guam's reefs
- Health of Guam's reefs
- - Health intro
- - Reef health tour
- - - - Northern reefs
- - - - East-central and southeastern reefs
- - - - Apra Harbor reefs
- - - -Southwestern reefs
- - - - Western reefs
- Threats to Guam's reefs
- - Algae overgrowth
- - Anchor damage
- - Coral bleaching
- - Crown of thorns outbreaks
- - Debris
- - Disease
- - Divers/snorkelers/ swimmers
- - Illegal fishing
- - Kayaks and other human-powered watercraft
- - Ocean acidification
- - Overharvesting
- - Sedimentation
- - Sewage discharge
- - Stormwater runoff
- - Terpios sponge
- - Vessel groundings
- - Windsurf boards and kiteboards
- Current management
- Recommendations
- Get involved

What are coral diseases?

In general, a disease is any abnormal condition of an organism that impairs physiological functions. A disease may be caused by infectious organisms, parasites, or unfavorable environmental, genetic, or nutritional factor. While we know little about what causes diseases of corals, what we do know is that they can be caused by bacteria, fungi, algae, and worms. Currently, about 30 diseases of corals have been identified on reefs around the world. Coral diseases have been found to affect dozens of coral species, including .

How do coral diseases affect coral reefs?

Coral diseases can partially or fully kill coral colonies, sometimes in a very short period of time (days to weeks). Coral diseases can have a devastating impact on coral reefs if the prevalance of disease (i.e., the ratio of diseased corals to healthy corals) is too great for coral communities to recover from. Unfortunatey, the frequence and severity of coral diseases - particularly in the Caribbean - have been increasing over the last few decades. In the Caribbean, vast areas of coral - including entire reef zones dominated by one or two vulnerable coral species - have been decimated by disease.

Large-scale disease outbreaks appear to be linked to warm water events; the diseases may become more dangerous to corals as the water warms, either because the corals are weakened when they lose their symbiotic algae or because the pathogens become more virulent - or both. It is also believed that nutrient- and sediment-laden runoff from land can cause coral diseases to become more dangerous to corals. While the level of impact from diseases observed in the Caribbean has not yet been realized across much of the Indo-Pacific, there is great concern that the impact of coral diseases - and diseases of other marine organisms - will continue to increase as water temperatures continue to rise and as development and poor land practices continue unabated.

How are coral diseases impacting Guam's reefs?

While relatively little is known about diseases affecting Guam's reefs, especially when compared with our understanding of diseases on Caribbean reefs, our knowledge of coral diseases on Guam is increasing with the work of researchers at the University of Guam Marine Lab. According to the 2008 State of the Coral Reef Ecosystems of Guam report, "coral disease surveys were conducted by the UOGML in 2006 and 2007 to establish baseline levels of coral disease. To date, 10 reefs have been surveyed for benthic composition, coral disease prevalence, and host species range..."

The results of the coral disease surveys indicate that diseases and syndromes affecting Guam reefs are similar to what has been reported elsewhere in the region. According to 2008 State of the Coral Reef Ecosystems of Guam report, "White Syndrome appears to be the most prevalent (observed in 9 out of 10 sites) and the source of greatest tissue mortality. Black Band Disease, the only documented circumtropical disease, is rare on Guam reefs, and has been observed primarily on massive Porites in Luminao Reef, but has also been observed at Tanguisson and in Sella Bay. The ciliate causal agent of Brown Band Diseasewas identified via microscopy in several species of Acropora from reef areas, such as Tumon Bay and Luminao Reef, containing thickets of such species. Growth Anomalies, which were the first diseases to be described from Guam, are more common, particularly on massive Porites. Ulcerative White Spots, first described from the Philippines, has been verified in Guam, though at very low prevalence. Other signs of compromised health have also been quantified, including Patchy Bleaching (different from temperature-related bleaching) and predation from the crown of thorns starfish, Acanthaster planci, and the gastropod snails, Drupella rugosa and Coralliophila violacea."

The report continues, "disease prevalence was highly variable within and between sites and did not show a strong relationship with live hard coral cover. Of the 10 surveyed reefs around Guam, three exhibited total prevalence values >10% (Luminao, Cocos Lagoon and Shark Pit Rock). While a baseline figure for total disease prevalence has not been established, using published literature as a guideline, it is reasonable to suggest that prevalence figures greater than 10% can be considered high and potentially problematic. Therefore, it appears from this initial census that disease may be causing at least partial mortality in a significant number of colonies in these reefs."

More information about the threat of coral diseases will be provided in the near future.