[Coral-List] here we go again

Gene Shinn eshinn at marine.usf.edu
Wed Jan 30 11:00:03 EST 2008

Did someone say "smear some on and see what 
happens...if you get an effect you are on to 

Sunscreen wipes out corals
Published online 29 January 2008 | Nature | doi:10.1038/news.2008.537
Study shows how chemicals can kill symbiotic algae.
Susan Brown

Keep the waters clean: divers are recommended not to use sunscreen.

Sunscreen can bleach coral reefs, researchers 
have confirmed. The chemicals that filter 
ultraviolet (UV) light can activate latent viral 
infections in the symbiotic microalgae that the 
corals rely on for nutrition.

Many divers are already warned not to wear 
sunscreen near corals, but usually for the 
general reason that introducing foreign chemicals 
into the water is a bad idea. The new study puts 
some scientific evidence behind this 
precautionary approach.

Resort managers in Mexico first spotted the 
trouble when enclosed pools called cenotes on the 
Yucatan Coast became popular swimming holes. 
"They saw a high mortality of all living things," 
says marine biologist Roberto Danovaro from the 
Polytechnic University of Marche in Ancona, 
Italy. Concerned that sunblock might be the 
culprit, several resorts banned its use by 
snorklers and divers exploring the cenotes and 
nearby reefs.

Danovaro and his co-workers set out to see 
whether they could prove the link between 
sunscreen and die-offs. They collected nubbins of 
coral from reefs scattered throughout the 
tropics: the Caribbean Sea off Mexico, the Indian 
Ocean off Thailand, the Red Sea off Egypt and the 
Pacific Ocean near Indonesia. When they incubated 
each sample in seawater spiked with as little as 
10 microlitres of sunscreen per litre, coral 
bleaching occurred within four days. Controls 
incubated in plain seawater remained healthy, the 
team reports in a forthcoming issue of 
Environmental Health Perspectives 1.

Viral attack

Before and after: corals are bleached by 
UV-screening chemicals.R. Danovaro/Polytechnic 
University of Marche

Samples of water drawn after 18-48 hours were 
full of symbiotic algae that had detached from 
the coral nubbins. Instead of a healthy brownish 
green, the loose algae were pale or transparent 
and punched full of holes. Viral particles were 
abundant as well, suggesting that the algae or 
coral harboured a latent infection that was 
activated by something in the sunscreens. "What 
was surprising to us was that the same latent 
infection was found in [corals from] so many 
places ’Äî all over the world," Danovaro says.

Danovaro and his team tested additional samples 
with several chemical components of suncreen and 
found that three UV-filtering chemicals (a 
cinnamate, a benzophenone and a camphor 
derivative) as well as butyl paraben, a 
preservative, caused the release of viral 
particles and bleached the coral. The other 
chemicals tested from the creams had no effect.

"I'm pretty convinced that viruses are 
instrumental in the whole bleaching process,’Äù 
says William Wilson, who studies marine viruses 
at the Bigelow Laboratory for Ocean Sciences in 
Boothbay Harbor, Maine, and was not involved in 
this work. Wilson and his colleagues have 
recently demonstrated that UV light can similarly 
prompt viral attacks2. "Coral bleaching seems to 
happen when the corals are stressed,’Äù he says. 
Attacking a weakened host is ’Äúa very classic 
response of a virus’Äù, he adds.

Some biologists have questioned whether effort 
should be expended on pinning down the effects of 
sunscreens, when warming waters and acidifying 
oceans clearly threaten more coral than do 
vacationers, who visit only about 10% of the 
world’Äôs reefs. Others counter that the threat 
from sunscreen is the easiest to control. "I'm 
not suggesting anyone should get burned," 
Danovaro says, "just that they use a physical 
sunscreen instead" ’Äî such as one based on 
titanium dioxide, or just a t-shirt.

          1. Danovaro, R. et al. Environ. Health 
Perspect. doi:10.1289/ehp.10966 (2008).
          2. Lohr, J., Munn, C. B. & Wilson, W. H. 
Appl. Environ. Microbiol. 73, 2976-2981 (2007). 

No Rocks, No Water, No Ecosystem (EAS)
------------------------------------ -----------------------------------
E. A. Shinn, Courtesy Professor
University of South Florida
Marine Science Center (room 204)
140 Seventh Avenue South
St. Petersburg, FL 33701
<eshinn at marine.usf.edu>
Tel 727 

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