In recent decades, people have started to notice the impact of light pollution such as skyglow on human’s health and ecological behaviour. Today, we will discuss light pollution and its impact on the aquatic ecosystem.
“We could see the light from the city being reflected across all the clouds all the way up, right above us, right over [the] top of us and off into the distance,”–Thomas Davies, a marine conservationist
Light Away from the Land
As described by Davies, artificial lights produced in the city is reflected back to the sky and can be clearly seen from off the coast. With the continuous growth of the human population, the expansion of human activities for globalisation and urbanisation is found to be the main source of light pollution.
All lifeforms are relatively sensitive to light, including marine species. Major coastal cities such as New York and Shanghai were illuminated by a massive amount of artificial lights at the night. With coastal area covered by artificial lights, marine species might be attracted to the shallow areas of the ocean at the wrong time. Artificial lights from the coastal areas, oil rigs, fishing activities or even vessels are also capable of penetrating through the water column into the deep seafloor.
“It’s brighter in cloudier conditions because more of the light of the city is being reflected back by the clouds,”–Thomas Davies, a marine conservationist
Recently, researchers from the University of Plymouth discovered that Light Emitting Diodes (LEDs) produced more short wavelengths that penetrated to the seafloor (Davies et al., 2020). Based on their study, 76% of green light and 70% blue light were managed to reach the seafloor during the low tides (Hershberger, 2020). However, red-light attenuates faster than blue and green light. The study also discovered a higher percentage of light penetration into the ocean on a cloudy night than on a cloudless night as the clouds were able to reflect the lights from the cities back to the ground or ocean (Hershberger, 2020).
As green and blue light have a stronger penetration level, marine lives are more sensitive to them than the weaker red-light. However, the use of artificial lights has potentially disrupted the natural biological cycle of the marine species. Some marine species relied on natural light (e.g. moonlight, Milky way) to regulate their behaviour such as sleep, searching for food and hideaway from predators (Carbonaro, 2020). Hence, marine species might be forced to reconstruct their natural behaviour to adapt to this situation.
Sea turtles are one of the few species that is highly affected by artificial lights. Normally, they rely on natural light to navigate their way after hatching at the beach. However, there are increasing incidents of artificial lights attracting baby sea turtles to the roads or civilisation instead of the sea, resulting in potential roadkill.
Mitigation
The International Dark-Sky Association (IDA) came out with the initiative of preserving nature dark skies. Although there was no specific focus on marine protected areas, “Marine Dark Sky Parks” might be a good mitigating approach in the future (Davies et al., 2016).
Currently, there is a general lack of awareness of light pollution and actions to mitigate such impacts on marine lives. Light pollution also illuminates another issue of ineffective use of resources as a huge amount of energy and resources are required to maintain the lights. Further research is required to explore the problems and implement feasible solutions to mitigate further impacts.
Cheers,
Shee Wen & Nicole 
References
Carbonaro, G. (2020). Study shows light pollution reaches the seafloor, harming marine life. Retrieved October 24, 2020, from https://newseu.cgtn.com/news/2020-08-18/Study-shows-light-pollution-reaches-the-sea-floor-harming-marine-life-T2jqRRELW8/index.html
Davies, T.W., Duffy, J.P., Bennie, J. & Gaston, K.J. (2016), “Stemming the Tide of Light Pollution Encroaching into Marine Protected Areas”, Conservation letters, vol. 9, no. 3, pp. 164-171.
Davies, T.W., McKee, D., Fishwick, J., Tidau, S. & Smyth, T. (2020), “Biologically important artificial light at night on the seafloor”, Scientific Reports, vol. 10, no. 1, pp. 12545-12545.
Hershberger, S. (2020). Light Pollution from Coastal Cities Reaches Seafloor. Retrieved October 24, 2020, from https://www.scientificamerican.com/article/light-pollution-from-coastal-cities-reaches-seafloor/