Sources

Overview

Light pollution enters the environment in the form of emanating light waves, of various wavelengths depending on the color of the light. Light pollution persists in the environment as long as the lights are on. Light pollution has prominent impacts at night as it disrupts natural nighttime conditions.

There are several sources of light pollution, some natural and some anthropogenic. Artificial sources of light pollution in the marine environment include ship lighting (a), city lighting (b), municipal and harbor lighting (c), lights from oil rigs (e), and light fisheries at squid spawning locations (f). Sources of natural light in the marine environment include moonlight (d), starlight, and natural fires.

Figure from Davies et al 2014. Satellite images from NASA/NOAA Suomi NPP satellite 2012.

What happens to light pollution once it enters the marine environment?

Light rapidly attenuates with depth in the ocean as the water absorbs the light. At 100 meters deep, 1% of the incoming light is available whereas deeper than 1000 meters there is no incoming light present. Various wavelengths penetrate to different depths, with blue and green light going the deepest. Light penetrates differently in open versus coastal waters. This is because coastal water has a higher concentration of phytoplankton and suspended sediment.

Light pollution has various potential impacts on the marine ecosystem

Artificial light sources during the night hours can impact marine life by disrupting biological processes, behavior, and interactions between organisms/species. Some of these impacts include hindering diel vertical migration of zooplankton (a), increasing bird strikes to lighted ships (b), increasing foraging hours for birds (c), larvae settlement selection interference (d), enhanced predation of fishes under lights (e), disruption of synchronous broadcast spawning (f), reducing sea turtle nesting areas (g), and reducing sea turtle hatchlings' migration to the sea (h).

Figure from Davies et al 2014.

Case studies of the impacts of light pollution on the marine ecosystem

Coral larvae settlement

Larvae settlement of the hood coral, Stylophora pistillata, was approximately 30% higher under ambient moonlight (control) in comparison to the two lighted groups (yellow and LED). This is significant because larvae settlement is directed by the spectra and intensity of light in the environment. Settlement success has implications for survival and reproduction of the population.

Figure from Tamir et al 2020.

Glow-worm reproduction

Female glow-worms, Lampyris noctiluca, glow during dark hours to attract mates. However, when exposed to artificial light a significant proportion of female glow-worms avoid glowing. This response reduces the success rate of attracting a mate and has implications for the survival of the population.

Figure from Elgert et al 2020.

Loggerhead turtle nesting attempts

When compared to a controlled dark environment, nesting attempts by loggerhead sea turtles were down 20.3% in red light, 21.7% in orange light, and 35.2% in yellow light. This poses the potential threat of turtles avoiding artificial light to nest in unsuitable locations like areas with dense vegetation or in high tide danger zones.

Table from Silva et al 2017.

Ghost crab activity

Out of 545 ghost crabs, 6.4% of activity occurred on dark nights, 52.7% under yellow light, 21.6% under orange light, and 19.3% under red light. This suggests that artificial light is a visual stimulant for ghost crabs, increasing their predation rate in artificially lit areas. In turn, this could potentially affect the predation of loggerhead sea turtle eggs that are under artificial lights.

Table from Silva et al 2017.

Amphipod abundance under LED and halogen lights

Amphipods are the most abundant source of food for planktivorous organisms such as fish and coral. The study showed that LED and halogen lights attracted amphipods which changes their availability in other places.

Figure from Navarro-Barranco et al 2015.

Convict surgeonfish settlement

Convict surgeonfish showed a significant preference for darker habitats for settlement. This suggests that artificial light treatment influences population dynamics in marine ecosystems like coral assemblages.

Figure from O'Connor et al 2019.

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