Substratum fidelity and early growth in Chelonibia testudinaria, a turtle barnacle especially common on debilitated loggerhead (Caretta caretta) sea turtles

The barnacle, Chelonibia testudinaria (Linnaeus, 1758), is reported to associate with nearly every species of sea turtle and is particularly common on loggerheads, Caretta caretta (Linnaeus, 1758), with symptoms of Debilitated Turtle Syndrome (DTS). Here, we test recruitment rates of C. testudinaria on various natural and artificial substrata, including carapace from healthy and debilitated loggerheads. In addition, the sizes of individual barnacles were followed through time to estimate early growth rates and to provide attachment duration estimates. Floating racks holding replicate panels of four treatments (DTS turtle carapace scutes, healthy turtle carapace scutes, Plexiglas®, and slate tile) were placed at four independent sites in Charleston County, South Carolina. Panels were monitored for 34–54 d. Our findings indicate that C. testudinaria larvae recruit and grow at significantly higher rates along the open shore vs protected areas, but do not recruit differentially to the four substratum types. Individual barnacle growth was highly variable within and between sites and substratum types; the mean growth rate was 4.28 mm d^–1 (95% CI: 3.42–5.14 mm d^–1). However, due to the high variability in growth, this value cannot serve as a fine-scale indicator for attachment duration. Further experiments of substratum selection and long-term survival are needed to fully clarify the nature of the barnacle/turtle association.