By Georgina Hopwood – 

It is no secret that sea turtles seem to be one of the primary victims of human degradation to the environment, being the poster species for campaigns against ocean pollution, plastic use, oil spills and general exploitation of marine life. However, we see much less information spread about light pollution and its damaging effects on the environment.

Figure 1 Turtle hatchlings crawling towards artificial light. The Impacts of Artificial Light on Sea Turtles by S. Long CC-BY via Ecological Society of Australia.

Known as a ‘keystone species’ for their importance to the ecosystem, sea turtles play a vital role in controlling the populations of their prey species, such as sponges, that are at risk of suffocating coral reefs [1,2], this is particularly important now because many reefs are endangered. Seagrass, which accounts for only 0.2% of the world’s oceans but stores about 10% of carbon buried in ocean sediment annually [3], is maintained by being grazed upon by sea turtles. This makes them important contributors to the local ecosystem as well as maintaining a key store of carbon [2]. A reduction in the number of nests could also result in increased coastal erosion as the nutrients left by unhatched eggs and hatchlings that didn’t survive, provide vital nutrients for coastal vegetation which aid in dune regeneration [2]. 

After sea turtles have hatched, they almost immediately head for the sea, guided by the light levels, usually, the moon reflecting off the water [5]. Because light is absorbed by vegetation on the beach, hatchlings crawl away from the darker land and towards the brighter seaward horizon [4]. When turtles have abnormal orientation, if they are confused by light pollution, they may take a longer route to the sea than is needed or start crawling inland [4]. It is estimated that only 1 in 1000 hatchlings will make it to adulthood [6], and hatchlings that don’t make it to the ocean quickly enough may die of dehydration or being preyed on by birds, crabs, or other beach-dwellers [1]. 

In an experiment conducted by Tuxbury and Salmon (2005), lights positioned against the ‘landward wall’ of a small environment in a laboratory were used to re-create the typical environment of a beach alongside a coastal road. One minute after the turtles hatched, their orientation was measured and the average orientation of the hatchlings was found to be facing inwards towards the lights instead of towards the ‘seaward wall’. This confirmed that the light pollution was affecting their ability to find the correct direction [4]. 

Although so far, conservation efforts in Florida have focused on preserving current dark beaches, we should also manage lighting at other beaches because even a small dark stretch of beach can lead to an increase of successful hatches [4]. Another solution to this problem is to focus conservation efforts on dune regeneration as sand dunes can create a silhouette in front of the lights, preventing as much pollution. 

While light pollution may not currently be considered to be as important as other threats to marine life, it can have devastating effects on sea turtles and consequently, the marine ecosystem as a whole. 

References and further reading

[1] Florida Fish and Wildlife Conservation Commission (2021) Sea Turtle FAQ. Available at: https://myfwc.com/research/wildlife/sea-turtles/florida/faq/ [Accessed: 9 November 2021].

[2] SEE Turtles (2021) Why Are Sea Turtles Important. Available at: https://www.seeturtles.org/why-are-sea-turtles-important [Accessed: 9 November 2021].

[3] The Blue Carbon Initiative (2021) What is Blue Carbon? Available at: https://www.thebluecarboninitiative.org/about-blue-carbon. [Accessed: 9 November 2021].

[4] S. M. Tuxbury and M. Salmon (2005) Competitive interactions between artificial lighting and natural cues during sea finding by hatchling marine turtles. Biological Conservation, 121(2), 311-316.

[5] Sea Turtle Conservancy (2021) Information About Sea Turtles: Threats from Artificial Lighting. Available at: https://conserveturtles.org/information-sea-turtles-threats-artificial-lighting/ [Accessed: 9 November 2021].

[6] SEE Turtles (2021) Baby Sea Turtles. Available at: https://www.seeturtles.org/baby-turtles [Accessed: 9 November 2021].