Anyone’s who strained to make out the Big Dipper at night knows that light pollution can be a problem in cities. But artificial light also affects less inhabited parts of the world, including nature reserves. In a new study, scientists searched for light pollution in marine protected areas — and found that some of these ocean refuges are getting brighter.

Artificial light can throw nature out of whack. Research has shown that unnatural nocturnal light disorients birds, delays salamanders’ foraging, and acts as a barrier to bats’ movements. One team estimated that from 1992 to 2010, artificial light levels rose in 7 to 42 percent of protected areas on land. The authors of the current study wondered whether the same pattern held true in protected parts of the ocean, which could be illuminated by ships, harbors, buildings along the coast, and offshore oil rigs and wind farms.

The team examined a map of more than 11,000 marine protected areas (MPAs) and images of night-time light taken from 1992 to 2012. The researchers found that 35 percent of the MPAs were exposed to some artificial night-time light in 2012. For nearly three-quarters of those exposed MPAs, light pollution was present in more than half of the pixels in the image. The problem was particularly common in the northwest Atlantic, Mediterranean Sea, Gulf of Mexico, Caribbean Sea, and coasts of Australia and eastern South America.

Over the study period, artificial light intensity rose in 15 percent of the MPAs and decreased in only 3 percent. Even among MPAs that were granted the strictest levels of protection, 9 percent became brighter.

Light pollution could get worse as more people flock to the coasts, developing countries become wealthier, and extraction of offshore energy resources moves into previously dark waters. Reversing the trend will be challenging: many people consider artificial light a normal and desirable part of modernization, and in some cases light may be required to meet safety standards.

But compromises are possible. For example, people could dim lights, shield rays from reaching the sea, and use wavelengths that don’t travel as far into the water. And unlike, say, ocean acidification, “changes to natural light regimes are comparatively instantaneous to reverse,” the authors point out. It might not be as easy as flicking off a light switch, but it’s closer. — Roberta Kwok | 25 June 2015

Source: Davies, T.W. et al. 2015. Stemming the tide of light pollution encroaching into Marine Protected Areas. Conservation Letters doi: 10.1111/conl.12191.

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