I’m not entirely sure why the “sunscreen causes coral bleaching” story is doing the rounds in the news again (see here and here – it seems to make for a very media-friendly story), but i’m still amazed at the mileage these authors are getting from a highly questionable study. I’ve debated this before on Climate Shifts with Robert Danavaro, the lead author of the study. Statements such as “New research highlights sunscreen as major cause of coral bleaching” are stretching the findings and conclusions of this paper to ridiculous extremes – the concept that “sunscreens may now be posing a significant risk to marine life” are missing the point. Durwood Dugger, the founder of the aquaculture company Biocepts wrote an excellent critique in response to my last post:

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.

I don’t doubt for a second that sunscreens kill corals – almost anything will cause mortality in high enough doses. A colleague of mine put this succinctly in a previous article:

“Any contaminant can experimentally damage a coral under artificially high concentrations. The amount [in the wild] must be tiny due to dilution,” commented Terry Hughes, director of the Australian Research Council’s Centre of Excellence for Coral Reef Studies at James Cook University in Queensland.

“Imagine how much water a tourist wearing one teaspoon of sunscreen swims through in an hour-long snorkel. Compared to real threats like global warming, runoff and overfishing, any impact of sunscreen is unproven and undoubtedly trivial,” he said.

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