Viral Effects on Coral

Although it may seem strange, viruses play a vital role in the health of coral reefs. Because viruses are extremely diverse and very organism specific, many different components of a coral colony may be affected by them. Viruses are known to infect coral polyp tissue, symbiotic algae called zooxanthellae, and bacteria. Perhaps the most detrimental effect a viral infection can have on a coral colony is to cause death to the zooxanthellae present in coral tissue. Under extreme conditions, viruses can cause cell lysis (rupture) in Symbiodinium species while living within coral. This prevents coral polyps from receiving any energy from the algae within them, and the eventual death of the colony (Van Oppen et al, 2008).

Additionally, coral-associated viruses could infect every component of a coral colony, from polyps to algae to microbes. One study was conducted to determine if viruses specifically attack parts of the coral colony, or attack it as a whole. The study concluded that there were viruses which infected the algal constituents of coral, the bacterial communities of coral, and the coral polyps themselves. The viruses were specific to the host they were found in. Many of the viruses were similar to ones found in other organisms. One in particular stood out: a herpes-like virus was found within the polyps of one coral specimen (Marhaver et al, 2008).

Interestingly, one study found that humans had an effect on viral infection and subsequent bleaching in coral. Sunscreen addition in all of the scientists’ sampling sites and replicates resulted in the release of copious amounts of coral mucous containing coral tissue and zooxanthellae. Furthermore, it was discovered that sunscreens significantly enhanced viral production in the ocean by inducing the lytic cycle – the process that destroys host cells – in virally infected bacteria living on and within coral. One study site was at Coconut Island in Hawaii, and the native Hawaiian species tested exhibited particularly intense bleaching as a result of the introduction of sunscreen to water (Danovaro, 2008).


Figure 1: Coral Bleaching due to Viral Infection. NOAA

-by Ben Dulas



Danovaro, Roberto, et al. “Sunscreens Cause Coral Bleaching By Promoting Viral Infections.” Environmental Health Perspectives 116.4 (2008): 441-447. Academic Search Premier. Web.

Marhaver, Kristen L., Robert A. Edwards, and Forest Rohwer. “Viral Communities Associated With Healthy And Bleaching Corals.” Environmental Microbiology 10.9 (2008): 2277-2286. Academic Search Premier. Web.

Van Oppen, Madeleine J. H., Jo-Ann Leong, and Ruth D. Gates. “Coral-virus interactions: A double-edged sword?.” Symbiosis 47.1 (2009): 1-8. Springer Link. Web.


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