LIGHT POLLUTION, A POTENTIAL THREAT TO THE ECOLOGY OF MARINE SYSTEMS?

Marine conservationists have long been concerned about the effects of artificial light on coastal ecosystems at night. Strong light scattered widely from coastal settlements, oil refineries, and other offshore structures can cause severe light pollution in the ocean. To test this further, marine biogeochemist Tim Smyth of Plymouth Marine Laboratory, UK, recently built a world map based on the brightness of the 2016 night sky, combined with ocean-atmosphere data. The data included airborne measurements of artificial light, satellite data collected monthly from 1998 to 2017 to estimate the prevalence of phytoplankton and light-scattering sediments, and computer simulations of how wavelengths of light penetrate seawater.

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Most species evolve in the natural and predictable state of moonlight, sunlight, and starlight. These institutions determine the activities of species (e.g. nocturnal, crepuscular, diurnal), offer useful navigational aids, help regulate and coordinate maturation and reproductive events, and provide a relatively constant spectrum of light that can regulate physiology and inform visually guided behaviors such as predation. and communication (Gaston et al. 2013).

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Natural cycles of light and darkness act as an exogenous factor affecting marine organisms in many biological, physiological, and behavioral processes, such as photosynthesis and partitioning of activity between day and night, including dark repair and recovery. Light pollution penetrates underwater, creating a very different world for fish that live on shallow reefs near urban environments. Light disrupts normal cues associated with circadian rhythms, which species have evolved over time through migration, reproduction, and feeding. Artificial light at night can make it easier for predators to find prey for smaller fish and can affect reproduction in reef fish. Perhaps the best-known impact of artificial light is the disorientation experienced by species that use natural light cues to navigate, particularly birds and sea turtles (Tuxbury and Salmon 2005) in marine systems. Meanwhile, beach lighting disrupts the orientation of hatchling turtles and prevents or delays their finding the sea (Tuxbury and Salmon 2005), which in turn reduces the number of turtle nesting sites on artificially lit sites ( Mazor et al. 2013).

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Artificial lights are commonly used by the fishing industry to attract and catch several species of squid. The light is so strong that nighttime satellite imagery can be used to measure fishing pressure, spawning grounds, and migration routes (Kiyofuji and Saitoh 2004). The widespread use of geographically powerful artificial lights in this fishery is likely to affect the behavior and survival of many nontarget and target species at large spatial scales. The intensity and spectrum of light are very useful cues by which organisms regulate their depth in pelagic environments where there are no landmarks. While some species have developed the ability to navigate horizontally through the detection of the Earth's geomagnetic field, the visible portion of the electromagnetic spectrum is one of the most important means of vertical navigation.

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Artificial light alters the spectrum and intensity of light experienced by the larvae, leading to the selection of a less-than-ideal site to colonize and transform into the adult form. The increase in artificial light intensity and broadening of the artificial light spectrum provides more opportunities for predatory species to spot prey compared to moonlight, potentially leading to diurnal and twilight foraging behaviors that extend further into the night, where nocturnal prey or predators crowd out species .from habitats previously only exposed to natural darkness. Anti-predator strategies include using light displays to confuse predators, sacrificing glowing body parts to distract predators, luring the predator itself, and mimicking ambient light from above to avoid predators recognizing silhouettes from below (Haddock et al.,year 2010). The effect of artificial light on this type of interaction is largely unexplored.

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The wider spectrum of artificial light that has been introduced recently means that visually-guided behaviors (such as mate selection) are more susceptible to light pollution, as many physical features used to communicate health are more discernible in white light (Davis et al. People. 2013). This includes the use of lamps that emit ultraviolet (UV) light, a communication channel that some species use almost exclusively to avoid predators or to distinguish closely related species (Siebeck et al., 2010). For example, the Ambon damselfish (Pomacentrus amboinensis) uses UV reflected in a species-specific pattern to distinguish similar species from other damselfish species that look the same in the visible wavelength range (Siebeck et al., 2010). Similar to fireflies, bioluminescent signals are also used by marine species for sexual communication (Haddock et al. 2010). The potential of artificial light to interfere with mating behavior dependent on bioluminescent cues has been raised with fireflies, artificial light may also interfere with such interactions in marine taxa.

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We raise awareness of the threat of artificial light to marine biodiversity and highlight some of the different species, behaviours, interactions and ecosystems that may be affected. Artificial light pollution is a global environmental problem, and its ecological impact is only now being studied in detail. Current understanding of these impacts on marine ecosystems is insufficient to determine the magnitude of the problem and its possible interactions with other anthropogenic pressures, nor to implement effective conservation measures. However, artificial light at night has the potential to disrupt some of the most biologically diverse and functional marine ecosystems and should therefore be considered a threat to human well-being.

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References

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Davies, Thomas W; Duffy, James P; Bennie, Jon; Gaston, Kevin J (2014). The nature, extent, and ecological implications of marine light pollution. Frontiers in Ecology and the Environment, 12(6), 347–355. doi:10.1890/130281

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Davies TW, Bennie J, Inger R, et al. 2013. Artificial light pollution: are shifting spectral signatures changing the balance of species interactions? Glob Change Biol 19: 1417–23.

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Gaston KJ, Bennie J, Davies TW, and Hopkins J. 2013. The ecological impacts of nighttime light pollution: a mechanistic appraisal. Biol Rev 88: 912–27.

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Haddock SHD, Moline MA, and Case JF. 2010. Bioluminescence in the sea. Annu Rev Mar Sci 2: 443–93.

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Kiyofuji H and Saitoh S-I. 2004. Use of nighttime visible images to detect Japanese common squid Todarodes pacificus fishing areas and potential migration routes in the Sea of Japan. Mar EcolProg Ser 276: 173–86.

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Mazor T, Levin N, Possingham HP, et al. 2013. Can satellite-based night lights be used for conservation? The case of nesting sea turtles in the Mediterranean. Biol Conserv 159: 63–72.

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Siebeck UE, Parker AN, Sprenger D, et al. 2010. A species of reef fish that uses ultraviolet patterns for covert face recognition. Curr Biol 20: 407–10.

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T.J. Smyth et al. A global atlas of artificial light at night under the sea. Elementa: Science of the Anthropocene. Published online December 13, 2021. doi: 10.1525/elementa.2021.00049.

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Tuxbury SM and Salmon M. 2005. Competitive interactions between artificial lighting and natural cues during sea finding by hatchling marine turtles. Biol Conserv 121: 311–16.