Influences of Wavelength and Intensity on Hatchling Sea Turtle Phototaxis: Implications for Sea-Finding Behavior

Visual cues are important to sea turtle hatchlings in determining seaward direction upon emerging from the nest. In this study, we examined the roles that color and intensity play in the sea-finding mechanisms employed by loggerhead (Caretta caretta) and green turtle (Chelonia mydas) hatchlings. We tested hatchling preference for a standard source of constant intensity and color (1.26 x 101 photons s-' m-2 at 520 nm), versus an adjustable light source (one of five monochromatic colors at each of seven photon intensities), using a two-choice apparatus. Both species oriented toward near-ultraviolet (360 nm), violet (400 nm), and blue-green (500 nm) light but chose the standard light source over yellow-orange (600 nm) and red (700 nm) light. There was a positive relationship between intensity and preference with 360, 400, and 500 nm light. We also examined hatchling choice of either a darkened window or a window lighted by one of eight monochromatic colors at each of two intensities. In these experiments, loggerheads oriented toward 360, 400, and 500 nm light but away from light in the green-yellow to yellow-orange range (560, 580, and 600 nm). Loggerheads oriented toward 700 nm light only at high intensity. Green turtles responded insignificantly to 600 or 700 nm light at either intensity. The contrast of green turtle behavioral responses with published electrophysiological data and the aversion to yellow light observed in loggerheads suggest some level of spectral quality assessment in sea finding for both species.