Coral larvae settle at a higher frequency on red surfaces
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Although chemical cues serve as the primary determinants of larval settlement and metamorphosis, light is also known to influence the behavior and the settlement of coral planulae. For example, Porites astreoides planulae settle preferentially on unconditioned red substrata. In order to test whether this behavior was a response to color and whether other species also demonstrate color preference, settlement choice experiments were conducted with P. astreoides and Acropora palmata. In these experiments, larvae were offered various types of plastic substrata representing three to seven different color choices. Both species consistently settled on red (or red and orange) substrata at a higher frequency than other colors. In one experiment, P. astreoides settled on 100% of red, plastic cable ties but failed to settle on green or white substrata. In a second experiment, 24% of larvae settled on red buttons, more than settled on six other colors combined. A. palmata settled on 80% of red and of orange cables ties but failed to settle on blue in one experiment and settled on a greater proportion of red acrylic squares than on four other colors or limestone controls in a second experiment. The consistency of the response across a variety of plastic materials suggests the response is related to long-wavelength photosensitivity. Fluorescence and reflectance spectra of experimental substrata demonstrated that the preferred substrata had spectra dominated by wavelengths greater than 550 nm with little or no reflection or emission of shorter wavelengths. These results suggest that some species of coral larvae may use spectral cues for fine-scale habitat selection during settlement. This behavior may be an adaptation to promote settlement in crustose coralline algae (CCA)-dominated habitats facilitating juvenile survival.
KeywordsCoral Planulae Metamorphosis Color Porites astreoides Acropora palmata
This project was facilitated by permits (FKNMS-2006-009, FKNMS-2006-026, FKNMS-20070114, FKNMS-2009-022) and logistic support from the Florida Keys National Marine Sanctuary. Funding was provided by the NOAA Coral Reef Conservation Program, Sanctuary Friends Foundation of the Florida Keys, and Henry Foundation. We gratefully acknowledge assistance from D.Williams, L. Johnston, and a multitude of others involved in fieldwork and larval culture for the project. R. Ritson-Williams assisted with the collection and identification CCA. G. Gaidosh and K. Voss enabled measurements of fluorescence and reflectance spectra. E. Borneman provided helpful discussion on methods. We also thank M. Schmale, R. Albright, A. Baird, and four anonymous reviewers for comments on the manuscript. M. Beard’s contribution (published here post-humously) was part of an internship conducted at the Southeast Fisheries Science Center as part of the Florida State University Certificate Program in Marine Biology.
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