[Coral-List] [EXTERNAL] Re: effect of sunscreen on corals

Hughes, Terry terry.hughes at jcu.edu.au
Thu Feb 7 03:09:34 UTC 2019

Hi Tim,

The crime I plead guilty to is investigating the legitimacy of statements made in recent legislation in Hawaii and Palau, which I refer to at the start of my article in The Conversation. 

For example, the Hawaiian law makers wrote:

"The legislature finds that two chemicals contained in many sunscreens, oxybenzone and octinoxate, have significant harmful impacts on Hawaii's marine environment and residing ecosystems, including coral reefs that protect Hawaii's shoreline.  Oxybenzone and octinoxate cause mortality in developing coral; increase coral bleaching that indicates extreme stress, even at temperatures below 87.8 degrees Fahrenheit; and cause genetic damage to coral and other marine organisms.  These chemicals have also been shown to degrade corals' resiliency and ability to adjust to climate change factors and inhibit recruitment of new corals."

Hawaii's reefs are in poor condition, but where is the scientific evidence that sunscreens have contributed to this decline - that they have inhibited recruitment or increased coral bleaching in Hawaii, or elsewhere? In Palau, sunscreens were referred to as "reef killers".

It seems that all of these statements on impaired reef resilience due to sunscreen refer back to just two laboratory studies. One of these looked at the effects of chemicals on day-old planulae of one species of coral, from Israel. The larvae bleached. (Brooded larvae have zooxanthellae). This appears to be the sole study that shows a potential effect on recruitment. 

Aquarium-scale experiments and field studies should go hand in hand. For example, lab studies that manipulate temperature and/or pH dovetail with regional and global studies of climate change and its impacts. But where are the corresponding field studies demonstrating an effect of sunscreens on juvenile and adults corals, or showing that sunscreen reduces recruitment onto a reef, or causes bleaching in brooded larvae or adults? They don't exist. 

There is clearly a lot of work to do to improve the rigour of water sampling to measure sunscreen chemicals. 

You can read my assessment of the evidence here: https://theconversation.com/theres-insufficient-evidence-your-sunscreen-harms-coral-reefs-109567

So is there any harm in banning sunscreen use for visitors to reefs? Potentially, yes, if it's a smokescreen for governments appearing "to do something", while largely ignoring a long list of tougher issues that are more important. In Australia, we have a "reef-rescue" program, while the government still promotes new coal mines.

Cheers, Terry

-----Original Message-----
From: Coral-List <coral-list-bounces at coral.aoml.noaa.gov> On Behalf Of Bargar, Timothy via Coral-List
Sent: Thursday, 7 February 2019 12:29 AM
To: Risk, Michael <riskmj at mcmaster.ca>
Cc: coral list <coral-list at coral.aoml.noaa.gov>
Subject: Re: [Coral-List] [EXTERNAL] Re: effect of sunscreen on corals

Mike - I agree that I don't understand the basis for Professor Hughes'
article.  Perhaps he is saying the bans on the use of some sunscreen chemicals is premature because of uncertainty about large scale effects?

A number of articles have demonstrated that, given sufficient exposure, some active ingredients are harmful to aquatic organisms, not just corals.
The key phrase is "sufficient exposure".  To quote Paracelsus, "sola dosis facit venenum", or, "the dose makes the poison".  In other words, at some point, the chemicals could result in a toxic response.  Many studies of the toxicity for sunscreen chemicals, not just the ones referenced by Professor Hughes, have exposed organisms to concentrations greater than what has been reported for marine surface waters.  But, some of the data in those studies, particularly in the articles by Craig Downs, show a response by coral at exposures close to some of the higher concentrations we found in the USVI.  In my humble opinion, this is not enough to suggest widespread risk, but it is sufficient to merit further investigation.

Tim Bargar, Ph.D.
Research Ecotoxicologist
The USGS Wetland and Aquatic Research Center
7920 NW 71st Street
Gainesville, Florida 32653
T - (352) 264-3520
F - (352) 378-4956

"Do not withhold good from those who deserve it when it's in your power to help them."
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