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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]

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 (Witherington & Bjorndal, 1991; Stanley et al., 2020). 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.

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 behavior 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[13]

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 behavior. 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 behavioral and survival impacts of light pollution during one of the most vulnerable stages of the sea turtle life cycle.[14]

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.[15]

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 behavior and habitat avoidance, hatchlings experience direct behavioral 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.


Given the impact, what are the solutions?

·      What are the local solutions, if any?

·      What are the global solutions, if any?

References

  1. ↑ 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 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. ↑ 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 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. ↑ 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. ↑ 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. ↑ Hu, X., et al. (2018). Artificial light pollution and sea turtle nesting: Evidence from Florida coastlines.
  14. ↑ 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
  15. ↑ 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
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