I was rung up today by a journalist who wanted me to comment on whether sunscreens could cause coral bleaching. Her question was triggered by an article published this month in Environmental health Perspectives by Danovaro, R. et al. (doi:10.1289/ehp.10966.) which shows that very small amounts of sunscreen can cause corals to bleach. This is potentially interesting given the often close association of tourists and coral reefs.
Looking closely at the paper, however, I think there may be a few problems. Whereas the article talks about ‘bleaching’ (which involves the specific movement of symbiotic dinoflagellates out of the coral tissue, which remains behind), the photo that accompanies the article shows a white coral which looks as if it has lost all of its host tissue. That is, the coral looks dead in my opinion rather than bleached.
Danovaro et al. (2008) also discuss the mechanism behind the putative bleaching caused by the sun screens. The authors saw a proliferation of viral like particles or VLPs in their ‘bleached’ specimens and concluded that the VLPs were responsible. Why did Danovaro and his team conclude this? Well, there are earlier pieces of work out of Willy Wilson’s laboartory, supposedly showing that mass coral bleaching is triggered by latent VLPs are triggered by elevated water temperatures (Lohr et al. 2007). Willy is pretty straight up about it. “I’m pretty convinced that viruses are instrumental in the whole bleaching process,” says William Wilson from the Bigelow Laboratory for Ocean Sciences Sciences in Boothbay Harbor, Maine (Nature News).
The final section of Lohr et al. (2007) is entitled “Implications for the mechanism of coral bleaching”. Based on the observation of lots of VLPs can be observed in stressed symbiotic anemones and three species of stressed corals, the paper concludes that VLPs are the reason for why corals bleach. Basically, temperature triggers VLPs which then attack the host and symbionts.
While I think the observation of VLPs in corals is very interesting, I find the evidence and conclusion that they cause of bleaching (or are part of the mechanism) less than convincing. The appearance of VLPs on stressed corals, just as with bacteria that are seen associated with many coral diseases, doesn’t allow us to conclude that they cause the coral to bleach or have a disease.
Isn’t it more likely that VLPs proliferate as a consequence of the dying corals/dinoflagellates as opposed to being the cause.
After all, 30% of all people that die on our roads will have the deadly bacterium Staphylococcus aureus on their skins, yet we would be incorrect to conclude that these poor victims died of Staphylococcus aureus (or that Staphylococcus aureus caused the road accident wounds).
Perhaps the conclusion that “VLPs cause mass coral bleaching” requires a touch of Ockham’s Razor (Principle of parsimony). What do you think?
I read with interest your commentary. As Author of the paper commented here I suggest to Prof. Ove Hoegh-Guldberg, which is apparently not a specialist in the field of microbiology, to read carefully the manuscript (incuding the supporting online material), to find the responses to the questions posed.
Prof. Hoegh-Guldberg should know that there is an important difference bewteen bacteria, which can be opportunistic pathogens, and viruses infecting the symbionts (that are causative agents of the cell death).
If you die by accident on a road you might be found infected by bacteria, but not by viruses (as they need to infect living cells to replicate…).
This just for love of the true… unless we don’t want to demonstrate that climate is the only thing that matters…
PS: the article is being published in 2008 not in 2007.
Thanks for the response. I will disregard your comment about my background (which makes little sense given the problem with your paper that I am pointing out). The point about the dead man in the street is not whether it is viruses versus bacteria but that you can’t prove the existence of a causal agent by correlation alone. The big jump that you and your coauthors make to conclude to mass coral bleaching being driven by a latent virus is not justified by the evidence. I think you are pushing this idea on too slim a data set. I am also amused by your comment on climate change driving bleaching – which unfortunately for us all is a far more justified and locked down case! By the way – we have had several students here looking for VLPs in real live bleaching events and finding nothing (done in association with Willy Wilson and a student – C. Munke). Seems that the idea that VLPs blossom under the atypical conditions of the laboratory requires serious consideration.
A final (very last) remark. To make a long story short, sunscreen kill the corals, if you don’t belive me, just try.
If you did not find viruses in corals please have a look at this paper just published on Coral Reef:
N. L. Patten, P. L. Harrison Æ J. G. Mitchell (2008) Prevalence of virus-like particles within a staghorn scleractinian coral (Acropora muricata) from the Great Barrier Reef. DOI 10.1007/s00338-008-0356-9
and then be sure that your several students are working well.
By the way I got appreciation about this work by Colin Munn.
Nonetheless I agree that further work is needed in this direction.
Kind regards and good luck for your future and extremely interesting research
As a marine scientist, an avid diver for over 45 years – I’m all for conserving the marine environment from human abuse. However, the science behind this particular sunscreen/coral bleaching research is extremely weak, incomplete and its conclusions neither demonstrated nor supported. The point of my comments herein is not to deny our coral reefs are not in danger, but to put this particular research in perspective critically and scientifically and to point out why its conclusions are not supported.
Here’s a key quote from the research paper in question “We tested sunscreen (10 μL L-1) containing concentrations of UV filters higher than those reported in most natural environments.” Actually, its massively higher than is likely to ever occur in ambient seawater in reef areas considering the relative an enormous dilution factors involved. Another fatal flaw in the research is that there is no large scale sampling from reefs around the world were accomplished to determine if sunscreen ingredients can even be detected in those waters or to correlate sunscreen use proximity with coral bleaching. The author says “Chemical compounds contained in sunscreens and other personal care products have been demonstrated to reach detectable levels in both fresh and seawater systems (Daughton and Ternes 1999; Giokas et al. 2007).” This statement is simply untrue – read the references listed. Both references offer very general extrapolated information and are not based (at least regarding coral reefs) on any specific insitu chemical analytical data. As such, neither reference provides any scientifically verified evidence of a direct link between sunscreen agents being measured in the seawater around reefs experiencing bleaching. Separating the effects of sunscreen from other far greater levels of other environmental pollution, or weather related stress events is not documented or well established in this research.
If the author had shown detectable levels of sunscreen ingredients (those ingredients that are not naturally found in background levels of seawater) in coral reef areas experiencing high levels of bleaching and in close proximity to sunscreen sources (sun bathing beaches) then a cause and effect relationship would have been supported – but it wasn’t. If the researchers had shown a proximity correlation map of sun bathing beaches, or snorkeling areas to reefs with high levels of bleaching that would also have helped to establish cause and effect relationships to support their theory – but they didn’t. What the researchers don’t mention is that many of the same chemicals found in sunscreen are found in many shampoos and body washes all of which end up in up in sewage and a lot which eventually finds its way into the oceans of the world. These products are used in many orders of magnitude greater than sunscreen around the world (including coral reef tourist areas) because they are used daily rather than just during weekends or annual vacations. Many high density tourism areas around the world use ocean outfall systems to dispose of their sewage, or near shore septic systems where the liquid fractions of treated sewage end up in the water table and as run off. Coral bleaching to the best of my knowledge has never been correlated to diver frequency/density (divers are the only people that are likely to be in close proximity to corals) – though physical damage to corals has been. Instead coral bleaching is occurring in wide spread areas both remote and highly trafficed. Why the researchers single out sunscreen products rather than the more obvious pollution sources of these chemicals to research – is not explained or well justified.
The supposition that sunscreen agents actually change the outcome of the viral epidemiology is also not well supported by science – and or typical viral epidemiology. Stress in general may decrease host immune function and increase viral infection rates and virulence in the short term, but the long term virulence effects are generally mediated by the virus and the host itself – otherwise you would have massive viral related species extinctions which only rarely if ever occur. That’s why the “promotion of viral infection” research theory is also not supported by general viral infection observation – other than as a potential and theoretical short term effect. Coral bleaching is a long term problem – and as such in my opinion a sunscreen/viral causal agent isn’t a significant probability for its primary cause. This in turn makes the conclusion that sunscreen is a significant factor in coral bleaching questionable as well.
The authors conclusions “We conclude that sunscreens, by promoting viral infection, can potentially play an important role in coral bleaching in areas prone to high levels of recreational use by humans.” are neither valid or supported scientifically, they are rather the author’s theories. While pieces of this research are informative – they are informative only under the exact conditions under which they were demonstrated – improbable levels of sunscreen contaminants. Essentially they don’t support any conclusion other than in the experimental environment described in the research – that the experimental levels of various sunscreen ingredients produce increased short term viral activity.
My point here is that while all pollution is a significant factor in environmental degradation and that residual pharmaceutical and personal care products in sewage are of particular concern and may well play a significant world wide role in marine environment degradation, incomplete research with exaggerated conclusions does not help the environment or environmentalism. It does promote the “Peter and the Wolf” syndrome that wears down the public, environmental managers and regulators, keeping them from making scientifically well informed decisions.
So where does that leave us as responsible stewards of the diving environments. If you’re diving in coral reef areas – wear sun protective gear rather than sunscreen – I think this most of us do this already. If you are swimming at a beach miles from any reef – use the minimal amount of sunscreen required to protect yourself based on your health risk factors. Always use the minimal amounts of personal care products necessary to accomplish their purpose and good health in general. If you aren’t a diver – avoid the coral reef areas of the world. If you are just a sun and beach person visit the sandy beaches in areas that don’t support coral reefs. Reefs around the world are getting way to much use and abuse from people who don’t know and care that they are even there. When your vacation is over – support responsible marine science research. Critically distinguish between literature that supports its conclusions scientifically and those that don’t. Think critically in all things. Ask questions and ask again if the answers don’t make sense. Be aware of the motivation of all informers. Be certain that you are well informed.
I have absolutely no beneficial relationship with anyone or companies producing sunscreens or related products. If you would like to read other critical commentary on this particular resource hear is an excellent one unrelated from mine.