[Coral-List] here we go again
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.
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
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
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.
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 virusÄù, 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
worldÄôs 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>
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