As coastal areas become increasingly developed, concerns are growing about levels of artificial light at night (ALAN) and its potential impacts on the marine environment.
Light pollution is well studied in terms of its effects on the night sky and astronomy, and on terrestrial ecosystems, but until now researchers didn’t know the full extent of ALAN in the oceans.
A new study, funded by the Natural Environment Research Council, maps out areas of the ocean most affected by light pollution, finding that up to 1.9 million sq km of the world’s coastal waters are being exposed to biologically significant levels of ALAN.
The study brought together researchers from the University of Plymouth, Plymouth Marine Laboratory, University of Strathclyde, The Arctic University of Norway, Bar-Ilan University, The Interuniversity Institute for Marine Sciences of Eilat and Beit Berl Academic College.
By combining various techniques including computer modelling, satellite technology and in situ observations in the River Tamar with a pre-existing world atlas of artificial night sky brightness, the researchers were able to build up a picture of the coastal ocean areas being exposed to ALAN.
In order to gauge artificial light in marine systems, the study used the light sensitivity of copepods (a type of microscopic crustacean) as a metric to determine the depth of light penetration.
Setting light levels by how detectable they are to marine organisms is key, considering the possible impacts of ALAN pollution on the creatures that live in the sea.
Many marine species are accustomed to the predictable light changes that occur naturally throughout the day, across seasons and with the lunar cycle. However, light from coastal developments can scatter a long way out to sea and is spectrally quite different to moon and sunlight. It also differs in the wavelengths penetrating the water column.
The new global atlas of ALAN under the sea shows that at a depth of one metre, 1.9 million sq km of coastal ocean are exposed to biologically important ALAN (around 3.1% of the global Exclusive Economic Zones). At 10m deep, 1.6 million sq km is exposed (2.7%) and by 20m down, 840,000 sq km (1.4%).