Can taller beach vegetation shield turtle nests from artificial light?

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Light pollution from poorly directed artificial lighting has increased globally in recent years. Lights visible along marine turtle nesting beaches can disrupt the natural brightness cues hatchlings use to orient toward the ocean for their offshore migrations. Natural barriers such as tall dunes and dense vegetation may reduce this disruption by blocking coastal and inland lights from the beach. Yet coastal areas are often managed for human values, including trimming vegetation to improve ocean views.

Researchers used viewshed models to examine how reducing the height of dune vegetation, specifically seagrape (Cocoloba uvifera), might increase artificial light reaching a marine turtle nesting beach in Southeast Florida from upland buildings. They combined three datasets—LiDAR data, turtle nest locations, and field surveys of artificial lights—in a geographic information system to create viewsheds of building lights across 21 vegetation profiles.

In 2018, when most seagrape patches had been trimmed to less than 1.1 m tall, female loggerhead turtles nested in areas with potential for high light exposure, according to a cumulative viewshed model. Models using random building selections through iterative simulations and nonrandom selections showed that untrimmed seagrape heights, averaging 3.1 m, and especially taller vegetation profiles effectively reduced potential exposure to lights at three building heights: upper story, midstory, and ground level. Even the tallest modeled vegetation, however, would not block upper-story lights from some tall buildings.

The findings can support decisions about trimming beach dune vegetation, associated changes in the visibility of artificial lights from nesting areas, and modifications to existing lighting needed to mitigate light exposure.