Barnacle Growth as an Indicator of the Onset and Duration of the Clinical Symptoms of Debilitated Turtle Syndrome Affecting Loggerhead (Caretta caretta) Sea Turtles
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Debilitated Turtle Syndrome (DTS) has become a growing concern for sea turtles in South Carolina, and in recent years (2000-2010) has accounted for an increasing percentage of loggerhead (Caretta caretta) strandings in the state. Although the causes of DTS are unknown, loggerheads stranding with DTS are characteristically emaciated, hypoglycemic, anemic, and heavily encrusted with epibiota. The illness is thought to ultimately weaken the turtle to the point that it floats at the water's surface, restricting the animal to an environment that predisposes it to heavy recruitment of the barnacle Chelonibia testudinaria on the carapace and soft tissue. The time it takes for debilitated loggerheads to manifest this heavy barnacle load is unknown. Our study measured how barnacle growth rate correlates with several environmental factors and experimentally tested whether barnacle recruitment on loggerhead scute varied between debilitated and non-debilitated individuals. Floating arrays holding test panels consisting of four treatments (debilitated turtle scute, non-debilitated turtle scute, Plexiglas, and slate tile) were placed at four independent experimental sites near Charleston, South Carolina. Results from two seasons (2009 and 2010) indicate that the larvae of the turtle barnacle C. testudinaria recruit at significantly higher rates along the open shore but do not recruit differentially to the four substrates. Growth rates for this barnacle are also higher in open water but do not vary with substratum type. Overall, individual barnacles had a mean growth rate of roughly 6.3 mm2/day on sea turtle carapace substrates.