An estimated 22.2% of global coastlines (excluding Antarctica) are exposed to artificial light pollution (Davies et al., 2014). Yet, marine light pollution remains very understudied, with most (already limited) research on light pollution centered on land-based light pollution.

Figure 1: Percentage of coastlines affected by light pollution across the world, 2012 (Davies et al., 2014)

Sources of marine light pollution include, and are not limited to, land-based infrastructures nearby, shipping vehicles, and natural sources of light such as the moon.

Figure 2: Sources of marine light pollution: (a)Artificial lights from ships anchored in Falmouth Bay, UK ; (b) Lights of Plymouth, UK, illuminating the Tamar Estuary and its creeks and tributaries ; (c) Decorative, harbour and municipal lighting spilling onto the Tamar, viewed from Cremyll, UK ; (d) Moonlight cast onto the shores of Cremyll in the Tamar Estuary, UK

 

The impacts of marine light pollution are wide-ranging, affecting not only marine animals but also migratory animals that course above the vast water bodies, such as migratory birds. More significantly, marine light pollution affects zooplankton, which forms the basis of marine ecosystems. Zooplanktons migrate vertically across the water column daily, coming to the water surface during the night to feed on phytoplankton, a type of microalgae. However, light pollution causes zooplankton to stay at the sea bed to avoid detection by predators, where reductions in the rate of zooplankton migration cause phytoplankton at the sea surface to proliferate. This upsets the aquatic balance of the ecosystem, and also prevents natural light from reaching the seabed – plants at the sea bed hence cannot receive sufficient light for photosynthesis.

Despite the impacts that marine light pollution has on biodiversity and marine ecosystems, light is currently not categorised as a pollutant under the guidelines by the International Convention for the Prevention of Pollution from Ships (MARPOL). The issue is complex as marine light pollution involves land-based sources, where the rate of light penetration through water bodies varies. It is also hard to quantify the exact impacts of artificial light on marine ecosystems, due to the lack of available research and literature.

 

References

‌ Davies, T.W., Duffy, J.P., Bennie, J. and Gaston, K.J. (2014). The nature, extent, and ecological implications of marine light pollution. Frontiers in Ecology and the Environment, [online] 12(6), pp.347–355. Available at: https://esajournals-onlinelibrary-wiley-com.libproxy1.nus.edu.sg/doi/epdf/10.1890/130281

Encyclopedia of the Environment. (2019). Impact of light pollution on aquatic organisms – Encyclopedia of the Environment. [online] Available at: https://www.encyclopedie-environnement.org/en/zoom/impact-of-light-pollution-on-aquatic-organisms/