Crab, Raccoon Play Tag Team Against Turtle

Abstract

SOCIETY FOR INTEGRATIVE AND COMPARATIVE BIOLOGY MEETING > SOCIETY FOR INTEGRATIVE AND COMPARATIVE BIOLOGY MEETING, 4–8 JANUARY, ORLANDO, FLORIDA Attempts by wildlife managers to help endangered Florida sea turtles may be backfiring. A field study on four beaches has shown there is a tradeoff between turtle-egg predation by raccoons and by ghost crabs that live in burrows along the beach. Management programs that remove raccoons from beaches have led to population booms in ghost crabs and even greater damage to sea turtle nests, says Brandon Barton, a graduate student in environmental studies at Yale University. While examining the stomach contents of raccoons as part of an evaluation of the effectiveness of removal programs, Barton realized that the mammals ate more than just turtle eggs: Ghost crabs made up more than 10% of the raccoons' diets. Wondering whether fewer raccoons resulted in more turtle nest raids by ghost crabs, Barton and James Roth, a community ecologist at the University of Central Florida in Orlando, surveyed raccoon and ghost crab populations and monitored turtle-egg predation at four sites: one where wildlife managers had trapped the mammals for the past 25 years; another where cages over turtle nests thwarted raccoon raids; and two where there was no raccoon control. ![Figure][1] Crime scene. Ghost crabs and raccoons can take quite a toll on sea turtle eggs and hatchings. CREDIT: BRANDON BARTON/YALE UNIVERSITY Active removal reduced the raccoon population, but the crab population was about double that at the other study sites, Barton reported at the meeting. At the trapping site, the mean body size of the crabs increased as well. Moreover, nest predation was 50% higher there—with about 30% of the turtle eggs disappearing. How much of this increased egg loss was due to ghost crabs is unclear, says Barton. Ghost crabs burrow into the sand to do their dirty work, and visits by raccoons obliterate telltale signs of crab activity. Barton also suspects that the crabs' burrows vent fumes from turtle egg and hatchling remains, helping the raccoon home in on nests. This work “will force people to rethink programs to remove raccoons from nesting beaches,” says Alessandro Catenazzi of Florida International University in Miami. Brent John Sinclair, a functional ecologist at the University of Nevada, Las Vegas, agrees: “It's another one of the classic examples of something that's not making any difference or making [a situation] worse.” [1]: pending:yes