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Conservation implications of density-dependent predation by ghost crabs on hatchling sea turtles running the gauntlet to the sea

Abstract

Protecting eggs from predators is common practice in sea turtle conservation, but routine protection of hatchlings is not. Of 42 loggerhead hatchlings observed emerging from 10 nests on undeveloped Onslow Beach, North Carolina, 24 % were preyed on by ghost crabs. In experimental trials, ghost crabs similarly threatened and captured neonate freshwater sliders, supporting their substitution as proxy for threatened and endangered sea turtle hatchlings in field experiments testing density dependence. Exploiting natural long-shore variation in ghost crab density, we show that a 2.6-fold higher ghost crab density resulted in 5 times more nocturnal threat encounters with sliders and 3.4 times more slider captures. Sliders released in simulated group emergences experienced lower per capita capture risk by ghost crabs than solitary sliders, implying predator dilution. Non-independence of egg and hatchling depredation motivates consideration of merging sea turtle egg and hatchling stages when modeling and managing food web interactions.

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Acknowledgments

We acknowledge the DCERP environmental funding program of the U.S. Department of Defense, which supported the sea turtle research done on Marine Corps Base Camp Lejeune (MCBCL) and under whose NOAA permit we conducted our Onslow Beach observations. We thank the many nocturnal nest watchers and turtle observers, including C. Biddle, L. Brown, C. Davis, L. Dee, B. Fegley, E. Fegley, J. Fegley, A. Karam, C. Martin, B. Maser, T. O’Meara, J. Meiners, J. Moore, C.B. Peterson, E. Schiffler, R. Schwartz, B. Steffan, M. Vance, Z. Vance, S. Vos, and E.L. Young. L. Pearson, J. Steube and C. Tenbrink of MCBCL provided access to important sea turtle nesting data. T. Wolcott suggested clever means of anticipating hatchling emergences. Comments on the manuscript by H. Marsh, S. Murphy, C. Osenberg, and anonymous referees are appreciated. We thank The Tortoise Reserve of White Lake and its Director D. Lee, under whose auspices, review, and permits the slider research was conducted.

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Correspondence to Charles H. Peterson.

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Communicated by R. Lewison.

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Peterson, C.H., Fegley, S.R., Voss, C.M. et al. Conservation implications of density-dependent predation by ghost crabs on hatchling sea turtles running the gauntlet to the sea. Mar Biol 160, 629–640 (2013). https://doi.org/10.1007/s00227-012-2118-z

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  • DOI: https://doi.org/10.1007/s00227-012-2118-z

Keywords

  • Beach
  • Green Turtle
  • Swash Zone
  • Active Burrow
  • Ghost Crab