Blog Post By: Ashlyn, Sea Turtle Intern
With signs plastered on every beach access, posters set up in the Camp exchange, and friendly night patrollers reminding us to only use red lights during turtle season, it’s hard to miss the fact that bright white lights can disturb our nesting turtles on the beach.
But what is the significance of using red lights as opposed to another color of light when turtles could be present on the beach?
Red light has the longest wavelength and is the first to be reflected out of the water column. Violet and blue light, on the other hand, has the shortest wavelength (and highest frequency), penetrating the deepest within the water column. Different species of turtles vary in responses in sensitivity to the color spectrum due to the prevalence of the color of light that is found in the aquatic habitats that they occupy. For example, freshwater turtles that live in shallow waters tend to have a greater sensitivity to longer wavelengths of light, such as orange and red light. In such shallow, freshwater aquatic systems, it is these long wavelength lights that are better transmitted throughout the water column. On the other hand, marine turtles have been found to be much more sensitive to shorter wavelength, blue and green, light that is better transmitted within deeper marine waters.
Sea turtles have adapted over time to respond to the light that is prevalent in their habitat. It’s no surprise, then, that the sea turtles coming to nest on our State Park Beach here at Edisto are the most sensitive to blue light that proliferates in deeper marine waters. There is still wide variation, however, in color sensitivity among sea turtles due to their life cycle habits. Loggerheads (Caretta caretta) that are the primary species seen nesting on Edisto tend to feed in shallow marine waters and have maximum diving depths of around 211-233 meters. Leatherbacks (Dermochelys coriacea) feed in the deeper open ocean and can dive to maximum depths of over 1000 meters. Research has suggested that Loggerheads have a higher sensitivity to a broad range of light wavelengths, processing blue, green, and yellow/orange, explained by their occupation higher in the water column. Leatherbacks’ sensitivity peaks at blue, with some capability of processing green, the colors that are transmitted within the deep marine water column.
Despite variations between sea turtle species in the wavelengths of light that are processed, red light is consistently processed with the least capacity among sea turtles. It is for this reason, that we as beach-goers are encouraged to use red lights when on the beach at night, as not to disturb our sea turtles that come to nest on the beach.
Kenneth W. Horch, Judith P. Gocke, Michael Salmon & Richard B. Forward (2008) Visual spectral sensitivity of hatchling loggerhead (Caretta caretta L.) and leatherback (Dermochelys riacea L.) sea turtles, as determined by single-flash electroretinography, Marine and Freshwater Behaviour and Physiology, 41:2, 107-119, DOI: 10.1080/10236240802106556
Sea Turtle Biologist