Abstract
Hatchling marine turtles emerge at night from underground nests on oceanic beaches and then use visual cues to crawl from the nest site to the sea (“seafinding”). However, the light wavelengths (λ’s) used to accomplish this orientation have not been thoroughly documented, nor do we understand why some λ’s are favored over others. We measured nocturnal radiance on the horizon at 20 nm intervals between 340 and 600 nm at two nesting beach sites and then, under laboratory conditions, determined the lowest intensities of those λ’s that induced green turtle and loggerhead hatchlings to crawl toward each light source (a low positive “phototaxis threshold”). Both species were similarly sensitive and were attracted to all λ’s. Radiance measures at all λ’s were greater toward the seaward horizon than toward the landward horizon, providing an important orientation cue regardless of variation in lunar illumination. Previous studies document that both species detect λ’s longer than those that are most attractive. We hypothesize that seafinding is a specialized response mediated by cones that are sensitive to the shorter λ’s (to minimize the effects of dark noise) but such as rods, are especially sensitive to low levels of nocturnal illumination.
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Acknowledgements
We thank K. Rusenko and D. Anderson of the Gumbo Limbo Environmental Complex for providing access to the sea turtle nests and hatchlings on the beach at Boca Raton, Florida. We thank T. Cronin and S. Johnsen for their responses to our frequent requests for advice and guidance. R. Forward loaned us many interference filters. His comments, and those of two anonymous referees, improved manuscript clarity and organization. LC completed this study as part of the requirements for a Master of Science degree in the Department of Biological Sciences at Florida Atlantic University. She thanks S. Kajiura and J. Wyneken, members of the thesis committee, for their advice and encouragement.
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Financial support was provided by the Department of Biological Sciences, Florida Atlantic University, and by the National Save-the-Sea-Turtle Foundation of Fort Lauderdale, Florida, USA.
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LC collected the hatchlings and did the experiments with the assistance of two undergraduate students, CS and AF. MS recommend the project and served as an academic advisor. LC and MS wrote the paper.
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The authors declare that they have no conflict of interest. This study was permitted by the Florida Fish and Wildlife Conservation Commission (TP 173) and approved by the Florida Atlantic University IACUC Committee (Protocol A16-22).
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Celano, L., Sullivan, C., Field, A. et al. Seafinding revisited: how hatchling marine turtles respond to natural lighting at a nesting beach. J Comp Physiol A 204, 1007–1015 (2018). https://doi.org/10.1007/s00359-018-1299-4
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DOI: https://doi.org/10.1007/s00359-018-1299-4