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Course:EOSC270/2023/Effects of Light Pollution on Sea Turtles

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What is the problem?

What is light pollution?

Light pollution is defined as the alteration of light levels in the outdoor environment due to man-made artificial sources of light [1]. This is often referred to as artificial light at night (ALAN) and is considered a major environmental issue in coastal ecosystems. For sea turtles, light pollution disrupts natural behaviours, particularly the ability of hatchlings to orient toward the ocean using natural light cues as the moon and horizon[2].

What human actions cause the problem?

Light pollution is caused by inefficient, excessive, or unnecessary use of artificial light, including:

  • Coastal development (hotels, homes, ports, and fishing boats)
  • Artificial lighting such as streetlights, floodlights, and building lights
  • Increased tourism and nighttime beach activity
  • Urban expansion along coastlines[3][4]

Where does the problem occur?

This problem occurs primarily on coastal beaches where sea turtles nest. It is most common in areas with high human development, such as tourist destinations and urbanized shorelines. Artificial lighting from nearby infrastructure can be visible from long distances, even up to tens of kilometers from the coast, affecting hatchling behaviour.[4]

How pervasive is the problem?

Light pollution is a widespread and growing global issue that affects many sea turtle nesting sites worldwide. Studies have shown that misorientation rates in hatchlings can range from 20-60% in areas affected by artificial lighting, demonstrating how significant the impact can be.[2][4]

How and why does it impact the identified ecosystems?

Light pollution impacts marine ecosystems by disrupting natural light-dependant behaviours that many species rely on for survival. In coastal environments, artificial light at night interferes with navigation, reproduction, and predator-prey interactions. For sea turtles, this disruption is most evident during the hatchling stage, where artificial light interferes with their ability to orient toward the ocean, ultimately reducing survival rates [1]. These individual level impacts can scale up, affecting population dynamics and ecosystem stability.

Are there unique characteristics of this habitat that make it vulnerable?

Coastal nesting beaches are particularly vulnerable because they are naturally dark environments where organisms have evolved to depend on subtle natural light cues. The flat, open landscape allows artificial light to spread easily across large areas, increasing exposure. In addition, these habitats are often located near areas of intense human activity, such as urbanized coastlines and tourist destinations, which increases the presence and intensity of artificial lighting[2].

Are there unique characteristics of these organisms that make them vulnerable?

Sea turtles are especially vulnerable because they rely on visual light cues immediately after hatching. This behaviour, combined with their nocturnal emergence, makes them highly sensitive to artifical light. Additionally, sea turtles have naturally low survival rates, meaning any small increase in mortality early on can cause a larger impact on population sustainability.[1]Ecosystem-Level Implications Declines in sea turtle populations can also impact broader marine ecosystems. For example, reduced populations can lead to decreased grazing on seagrass and algae, which may disrupt ecosystem balance and contribute to trophic cascade effects in systems such as coral reefs[3]

Effects of Light Pollution on Sea Turtles

Sea turtle hatchling disoriented by streetlight

Effects on Hatchlings

Sea turtle hatchlings are highly vulnerable to artificial light at night because their survival depends on correctly orienting toward the ocean immediately after emerging from the nest. Under natural conditions, hatchlings use visual cues such as the brightness of the open horizon over the sea, reflections of moonlight on the water, and the darker silhouette of dunes and vegetation behind them to guide their movement. This behavior, known as phototaxis, is critical for ensuring that hatchlings reach the ocean quickly and begin their offshore swim.[5]

Disorientation & Misorientation

Artificial light disrupts these natural orientation cues, often causing hatchlings to move in the wrong direction. This phenomenon can result in two main behavioral responses: disorientation, where hatchlings wander without a clear direction, and misorientation, where they move consistently toward artificial light sources such as streetlights, buildings, or beachfront developments. Studies have shown that even relatively low levels of artificial light can override natural cues, leading hatchlings inland instead of toward the sea.[6][7]

Increased Mortality Risk

When hatchlings are misoriented, their chances of survival decrease significantly. Prolonged time on land exposes them to predators such as birds, crabs, and mammals, while also increasing the risk of dehydration and exhaustion[8]. Additionally, hatchlings that travel longer distances expend valuable energy reserves needed for their initial offshore swim, reducing their likelihood of surviving early life stages[9]. Artificial light can also attract hatchlings to illuminated waters, further altering their movement patterns and increasing predation risk in nearshore environments[10].

Influence of Light Wavelength and Intensity

The impact of artificial light on hatchlings is strongly influenced by both wavelength and intensity. Research has shown that hatchlings are particularly sensitive to shorter wavelengths (e.g., blue and white light), which are more likely to disrupt orientation behavior[6]. In contrast, longer wavelengths such as amber or red light have a reduced effect on hatchling disorientation and are often recommended for wildlife-friendly coastal lighting. Higher light intensities also increase the likelihood and severity of misorientation, making brightly lit coastal areas especially harmful.[11][7]

Interaction with Environmental Factors

The severity of light pollution effects can vary depending on environmental conditions. Natural light sources such as moonlight and starlight can partially counteract artificial lighting, but in heavily urbanized areas, artificial light often dominates the visual environment[5]. Beach characteristics, including slope and vegetation cover, also influence how light is perceived by hatchlings, with flatter, more open beaches being more susceptible to light pollution impacts[12]. Coastal development further amplifies the problem by increasing both the intensity and spatial extent of artificial lighting.

Impacts on Sea Turtles Predator and Prey Relationship

Within marine ecosystems, a serious risk of artificial light pollution, that is typically overlooked, are the effects it has on the relationship between predators and prey.

A species that clearly illustrates this disruption, are the sea turtles, in which their ability to survive is strongly dependent on natural light cues. As discussed in the earlier section of this paper, this is apparent because marine turtle hatchlings are increasingly more attracted to lights, leading them to crawl away from safe environments[6]. A study supported this claim, showing that when hatchlings are in contact with excessive amounts of artificial light, their chances of survival decrease significantly[8].

Effects of Light Pollution on Sea Turtles and Ghost Crabs

In this study, sea turtles and their predator, ghost crabs, were tested under yellow, orange and red lights, to identify any behavioural changes between them[8]. Since ghost crabs are nocturnal, it is predicted that artificial lighting, at night, would alter their natural behaviours[13]. Results concluded that when marine turtles are exposed to artificial lighting, they become confused and disoriented, leading them to spend more time on the beach, nesting, and traveling into unsafe areas, instead of completing the process efficiently[8]. Moreover, the study showed that illuminated areas had an increased number of ghost crabs present, in which the yellow lighting had caused a major change in their behaviour, making them increasingly more aggressive leading to intensified predatory behaviours[8]. Whereas, crab activity under red lights had no substantial difference[8].

The crabs were more attracted to the illuminated areas of yellow lights because it acted as an “artificial” food supply, due to the increased number of insects attracted to the lights, which they also feed on[8]. In addition, the study conducted an experiment that consisted of placing a hotdog or a dead hatchling in the illuminated area, during which the crabs immediately recognized the food source and rapidly preyed upon it[8]. As a result, these effects on both ghost crabs, and hatchlings could cause increased predation on marine turtles by ghost crabs[8]. Ultimately, marine turtles get confused in the presence of artificial lighting, luring them into the illuminated regions in which predatory ghost crabs, who are also drawn to these lights, present intense aggressive behaviour towards their prey, leading to an increase in marine turtle predation[8].

What is the extent of the problem?

Case Studies

Empirical studies from different regions provide strong evidence that artificial light at night affects sea turtles across multiple stages of their life cycle, from nesting behaviour in adults to orientation and survival in hatchlings.

Florida Coast, United States

Coastal nesting habitat for sea turtles along the Florida shoreline

A large-scale geospatial study along the Florida coastline examined the relationship between artificial light at night and sea turtle nesting density. Using satellite data and spatial analysis, researchers found a significant negative correlation between light pollution and nest density across multiple species, including green turtles, loggerheads, and leatherbacks[14]

Beaches with higher levels of artificial light consistently had lower nesting densities, suggesting that adult female turtles actively avoid brightly lit areas when selecting nesting sites. This behavioral avoidance reduces overall nesting success and may lead to long-term population declines if suitable dark beaches become limited.

Lanyu Island, Taiwan

Coastal habitat on Lanyu Island, Taiwan, a sea turtle nesting region

A field-based experimental study conducted on Lanyu Island investigated how artificial light affects hatchling sea-finding behaviour. Under natural conditions, hatchlings rely on the brightness of the ocean horizon to orient themselves toward the sea. However, the study found that artificial light frequently caused disorientation and misorientation, preventing hatchlings from reaching the ocean.

In some trials, nearly 90% of hatchlings failed to successfully reach the ocean when exposed to artificial lighting. The study also demonstrated that shorter-wavelength light (e.g., white light) had stronger disruptive effects compared to longer wavelengths such as yellow light, and that shielding artificial light sources improved orientation outcomes.

These findings highlight the direct behavioural and survival impacts of light pollution during one of the most vulnerable stages of the sea turtle life cycle.[15]

Mediterranean Region (Kyparissia Bay, Greece)

Undeveloped sea turtle nesting beach in Kyparissia Bay, Greece

A recent study in Kyparissia Bay, one of the most important sea turtle nesting areas in the Mediterranean, assessed exposure to artificial light across nesting beaches. The study found that light pollution was unevenly distributed, with particularly high illumination near developed areas such as Kalo Nero, where levels reached up to 11.1 Lux.

These highly illuminated areas showed significantly lower nesting densities, while darker, less developed beaches supported higher nesting activity. The study also identified potential risks to hatchlings, as increased light exposure can disrupt orientation and increase mortality through predation and energy depletion.

By combining spatial mapping with field measurements, this study demonstrates how coastal development expands the reach of light pollution and threatens critical nesting habitats at a regional scale.[16]

Synthesis of Findings

Together, these case studies demonstrate that light pollution is a multifaceted environmental stressor affecting sea turtles at both individual and population levels. While adult turtles are impacted through altered nesting behaviour and habitat avoidance, hatchlings experience direct behavioural disruption that reduces survival. Across regions, consistent patterns show that increasing artificial light leads to decreased nesting success and higher hatchling mortality, highlighting light pollution as a significant and growing threat to sea turtle populations.

What are the Solutions?

After learning about the continuous effects that artificial light has on sea turtles, it is important to create and execute solutions, to reverse or prevent these disruptions from occurring. For instance, some mitigation strategies include, utilizing red lights rather than yellow or white lights, trimming vegetation strategically, and adjusting the coastal light beams direction.

1) Using Red Lights, Instead of White or Yellow Lights

Firstly, one of the biggest, most supported mitigation strategies is, using red wavelength coastal lightings instead of white or yellow. One of the reasons why, is due to the fact that studies have shown that marine turtles are increasingly more sensitive to lights of shorter wavelength, in comparison to those of longer wavelengths[6].

Sea turtles have adapted to identify lights of shorter wavelength, because their natural habitats are marine environments, in which blue light (shorter wavelength) prevails, since it penetrates deeper depths of water than red light (longer wavelength)[17][6]. Due to this adaptation, sea turtles are less sensitive to longer wavelength lights (ex. red lights)[6]. Therefore, as mentioned earlier in this paper, since natural light cues are utilized by female turtles, in order to locate and examine the safety of the nesting site, having artificial lights near these areas could affect the nesting process[8]. This can occur because, as stated previously, brighter and shorter wavelength lightings typically confuse and disorient sea turtles; as a result, complicating the process of nesting site selection, which contributes to the decrease in the amount of nesting attempts[8]. In addition, since many sea turtles are nocturnal nesters, having artificial lighting near their nesting areas can lead them to think it is daytime, and therefore reducing successful nesting attempts[18]. However, studies have shown that using different wavelengths of lights can have varying results on marine turtles nesting attempts.

For example, a study done by Silva et al. (2017), tested the impacts of red, orange, and yellow lights on the nesting activity of sea turtles, in which results showed, when compared to trials with no artificial lighting, that there was a 20.3%, 21.7%, and 35.2% decrease in nesting attempts when red, orange and yellow lights were used respectively[8]. This can be due to the fact that yellow and white lights have shorter wavelengths than red and orange lights, causing increased levels of misorientation and overall disruptions to sea turtles[8]. Ultimately, these findings support the idea that changing the coastal artificial lights to red, is a reliable mitigation strategy to help reduce the effects of light pollution on sea turtles.

2) Strategically Trimming Vegetation

The next mitigation strategy consists of strategically trimming vegetation that resides near sea turtle nesting areas. Studies have concluded that cutting beachfront vegetation leads to more exposure of artificial light on the nesting sites[12]. The reason for this is because maintaining relatively dense and tall vegetation helps block ground level and midstory lighting, in comparison to regularly trimmed vegetation[12]. In a study conducted by Barrett & Sella (2022), evidence established that when vegetation is left untrimmed, near nesting sites, the surrounding hatchlings were not disturbed by the lights[12]. As a result, trimming those vegetations after peak nesting seasons could be an effective mitigation strategy against the effects of artificial light pollution on marine turtles.

An example of unshielded lights.

3) Altering Direction of Light Beams

Finally, various studies have shown that altering the direction of coastal light beams negates the effects of light pollution on sea turtles. Since artificial light pollution at night is increased by insufficient lighting designs that lead to scattering of light in excessive areas, adding shields to the lights can reduce the consequences[19][20]. Since, 25% of light pollution is due to the light fixtures reflections, shielding artificial lights decreases 25% of sky brightness; decreasing the number of disoriented turtles[19]. Nevertheless, directing the light beams only to required areas, through the use of shields, is a functional mitigation strategy[19]. This is ultimately because shielding light fixtures decreases the amount of illuminated area, and instead meaningfully directs the light beams towards specific regions, limiting the amount of disruptions on sea turtles[19].  


References

  1. ↑ 1.0 1.1 1.2 Hollan, J. (2006). What is light pollution, and how do we quantify it? https://amper.ped.muni.cz/light/lp_what_is.pdf
  2. ↑ 2.0 2.1 2.2 Gomez Isaza, D. F., Jones, R., Wilson, P., Pendoley, K., Fossette, S., & Thums, M. (2025). The effect of artificial light at night on sea turtle hatchling early dispersal: A systematic review of methods, impacts and findings. Biological Conservation, 309, 111327. https://doi.org/10.1016/j.biocon.2025.111327
  3. ↑ 3.0 3.1 Salmon, M. (2003). Artificial night lighting and sea turtles. 50(4), 163–168. https://www.researchgate.net/publication/283857765_Artificial_night_lighting_and_sea_turtles
  4. ↑ 4.0 4.1 4.2 White, D., & Moll, D. (1991). Clutch Size and Annual Reproductive Potential of the Turtle Graptemys geographica in a Missouri Stream. Journal of Herpetology, 25(4), 493. https://doi.org/10.2307/1564778
  5. ↑ 5.0 5.1 Tuxbury, S. M., & Salmon, M. (2005). Competitive interactions between artificial lighting and natural cues during seafinding by hatchling marine turtles. Biological Conservation, 121(2), 311–316. https://doi.org/10.1016/j.biocon.2004.04.022
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Witherington, B. E., & Bjorndal, K. A. (1991). Influences of wavelength and Intensity on Hatchling Sea turtle Phototaxis: Implications for Sea-Finding Behavior. Copeia, 1991(4), 1060. https://doi.org/10.2307/1446101
  7. ↑ 7.0 7.1 Stanley, T. R., White, J. M., Teel, S., & Nicholas, M. (2020). Brightness of the Night Sky Affects Loggerhead (Caretta caretta) Sea Turtle Hatchling Misorientation but Not Nest Site Selection. Frontiers in Marine Science, 7. https://doi.org/10.3389/fmars.2020.00221
  8. ↑ 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 8.11 8.12 8.13 Silva, E., Marco, A., Da Graça, J., Pérez, H., Abella, E., Patino-Martinez, J., Martins, S., & Almeida, C. (2017). Light pollution affects nesting behavior of loggerhead turtles and predation risk of nests and hatchlings. Journal of Photochemistry and Photobiology B Biology, 173, 240–249. https://doi.org/10.1016/j.jphotobiol.2017.06.006
  9. ↑ Truscott, Z., Booth, D. T., & Limpus, C. J. (2017). The effect of on-shore light pollution on sea-turtle hatchlings commencing their off-shore swim. Wildlife Research, 44(2), 127. https://doi.org/10.1071/wr16143
  10. ↑ Thums, M., Whiting, S. D., Reisser, J., Pendoley, K. L., Pattiaratchi, C. B., Proietti, M., Hetzel, Y., Fisher, R., & Meekan, M. G. (2016). Artificial light on water attracts turtle hatchlings during their near-shore transit. Royal Society Open Science, 3(5), 160142. https://doi.org/10.1098/rsos.160142
  11. ↑ Gammariello, R. T., & Dunbar, S. G. (2025). Thresholds of visible light detection in hawksbill turtle (Eretmochelys imbricata) hatchlings. Regional Studies in Marine Science, 89, 104337. https://doi.org/10.1016/j.rsma.2025.104337
  12. ↑ 12.0 12.1 12.2 12.3 Barrett, M. A., & Sella, K. N. (2022). Modeling Artificial Light Exposure after Vegetation Trimming at a Marine Turtle Nesting Beach. Remote Sensing, 14(11), 2702. https://doi.org/10.3390/rs14112702
  13. ↑ Steiner, A. J., & Leatherman, S. P. (1981). Recreational impacts on the distribution of ghost crabs Ocypode quadrata fab. Biological Conservation, 20(2), 111–122. https://doi.org/10.1016/0006-3207(81)90022-7
  14. ↑ Hu, X., et al. (2018). Artificial light pollution and sea turtle nesting: Evidence from Florida coastlines.
  15. ↑ Yen, C.-H., Chan, Y.-T., Peng, Y.-C., Chang, K.-H., & Cheng, I.-J. (2023). The effect of light pollution on the sea-finding behavior of green turtle hatchlings on Lanyu Island, Taiwan. Zoological Studies, 62, 47. https://doi.org/10.6620/ZS.2023.62-47
  16. ↑ Simantiris, N., Vardaki, M. Z., Dimitriadis, C., Netzipi, O., & Malaperdas, G. (2025). Assessing light pollution exposure for the most important sea turtle nesting area in the Mediterranean region. Journal of Marine Science and Engineering, 13(10), 2020. https://doi.org/10.3390/jmse13102020
  17. ↑ Soja-Woźniak, M., Holtrop, T., Woutersen, S., Van Der Woerd, H. J., Lund-Hansen, L. C., & Huisman, J. (2025). Loss of sea ice alters light spectra for aquatic photosynthesis. Nature Communications, 16(1), 4059. https://doi.org/10.1038/s41467-025-59386-x
  18. ↑ Witherington, B. E. (1992). Behavioral Responses of Nesting Sea Turtles to Artificial Lighting. Herpetologica, 48(1), 31–39. http://www.jstor.org/stable/3892916
  19. ↑ 19.0 19.1 19.2 19.3 Di Bari, D., Tiberti, C., Mazzei, E., Papetti, L., Pagli, D., Corfitsen, M., Davies, T., Duffy, J., Bennie, J., Gaston, K., Davies, T., Duffy, J., Bennie, J., Gaston, K., Davies, T., Smith, T., Falchi, F., Cinzano, P., Elvidge, C., . . . Witherington, B. (2023). Light Pollution and Sea Turtles Nest-Site Selection. Is it Possible a Practical Management of the Problem? European Journal of Sustainable Development, 12(2). https://doi.org/10.14207/ejsd.2023.v12n2p35
  20. ↑ Falchi, F., Cinzano, P., Elvidge, C. D., Keith, D. M., & Haim, A. (2011). Limiting the impact of light pollution on human health, environment and stellar visibility. Journal of Environmental Management, 92(10), 2714–2722. https://doi.org/10.1016/j.jenvman.2011.06.029
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