Oceans under siege: Sunscreens add to toll on reefs

It is our task in our time and in our generation to hand down undiminished to those who come after us, as it was handed down to us by those who went before, that natural wealth and beauty which is ours.

— President Kennedy, dedication of National Wildlife Federation Building in 1961

While the world worries and debates about increasing carbon dioxide in our atmosphere, a more insidious and perhaps irreversible change threatens the oceans.

Like the air we breathe, oceans represent a dumping ground for the gases released when human beings burn fossil fuels. Marine waters have absorbed approximately half of the carbon dioxide released from industrialization, and the resulting phenomenon is termed ocean acidification.
Although oceans are not truly acidic yet (by technical definition, an acid has a pH value less than 7.0), their pH is dropping from a basic value (greater than pH of 7) to an acidic metric on the pH scale. Oceanographers estimate that the ocean absorbs about 22 million tons of carbon dioxide per day and that — by the end of the century — the upper 300 feet of sea water will be more acidic than at any time during the last 20 million years.

Increasing acidity is akin to creating toxic soup, and acidity significantly degrades the environment for oceanic life. A big question asked by scientists, scuba divers, fishermen and the tourism industry is: What impact will ocean acidification have upon marine ecosystems, especially fish and coral reefs?

The prognosis is not good. Organisms that produce hard-bodied structures — snails, corals, clams — may be unable to survive. Increased levels of carbon dioxide prevent the calcification process that is key to construction of the exterior structures of many marine organisms. Biologists predict that if atmospheric carbon dioxide reaches concentrations of 450-500 parts per million (on our current trajectory, this level is achievable by 2050), then coral reefs will cease to grow, creating underwater dead zones of skeletal coral structures.

Obviously, if coral reefs disappear, their resident fish populations will no longer have homes, and they too will disappear. The loss of coral reefs and fish populations has enormous consequences to tourism, to what we eat, to food chains that link to land, to biodiversity, to potential medicines from marine organisms, to cultures and to the aesthetics of our environment.

In addition to the acidification challenge, increased carbon dioxide in oceans leads to increased temperatures. Warmer waters cause coral bleaching, where the partnership between soft-bodied coral animals and their resident algae is terminated, resulting in death of the reef. The algae living in coral structures are called zooxanthellae (pronounced zoo’-xan-thell-ee), and this unique animal-plant partnership forms the building block of a coral reef.

Warmer water and increased acidification are formidable challenges in their own right, but one additional human activity is further threatening coral reefs. Marine biologists have discovered that the compounds used in sunscreens kill the algae which live in partnership with the corals. Coral bleaching has increased over the past decades, and at the same time, numbers of visitors to coral reefs have increased dramatically.

A team at the University of the Marche in Ancona, Italy, found that sunscreen ingredients kill the algal partners that live with corals. An estimated 25 percent of sunscreen application washes off the typical swimmer or snorkeler visiting a coral reef, and this level of personal sunscreen in the water killed the algae (i.e., zooxanthellae) within four days.

The sunscreen chemicals trigger dormant viruses within the algae that subsequently infect and kill it. An estimated 4,000 to 6,000 metric tons of sunscreen bombard coral reefs each year, according to conservative estimates.

So how does a tropical tourist balance the advice of her skin doctor, which may be in direct conflict with an ethical sense to conserve coral reefs?

Two possible solutions exist: Use sunscreens with physical (not chemical) filters such as zinc oxide, because they do not cause mortality of coralline algae. Or second, wear clothing instead of applying chemicals, because the fabric may provide a more effective sunblock and does not contribute toxins to coral reefs.

Sunscreen, pollution, acidification, warming water — our precious coral reefs are victims of myriad human activities that wreak irrevocable death and destruction.

Snorkelers, scuba divers, fishermen and marine biologists all share a stake in the future health of our marine waters and especially our coral reefs. We need to work together to educate the public about conservation of these wonderful marine treasures. “Save our reefs” is a critical mantra for the next few years of important environmental decision-making.

Margaret Lowman, HeraldTribune.com, 19 May 2008. Article.

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