Investigating the attachment biology of the tassel barnacle, <i>Xenobalanus globicipitis</i> and its incidence on dead and debilitated dolphins
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Epibionts live on the surface of a basibont or host organism in a commensal relationship. Finding and attaching to a host may be influenced by chemical cues released from the host and received by the epibiont via olfaction. The tassel barnacle, <i>Xenobalanus globicipitis</i>, lives exclusively attached to dolphins, which are otherwise clear of commensals. The mechanism by which the barnacle finds and attaches to host is not yet understood. This study aims to (1) further understand the settlement biology of tassel barnacles and (2) provide a comprehensive review of their prevalence on dolphins stranded in South Carolina and Georgia. The first objective of this study was to extract lipid- and protein-containing fractions from dolphin skin and test the hypothesis that either or both of these constituents induce the settlement of <i>X. globicipitis</i>. Protein and lipid fractions were extracted from skin obtained from a stranded dolphin. Larvae were harvested from gravid <i>X. globicipitis</i> individuals, reared to settlement stage, and exposed to gel substrates containing the extracted dolphin skin proteins, lipids, both, or nothing. While <i>X. globicipitis</i> settlement trials were inconclusive in determining the involvement of a protein or lipid in settlement, the study did yield positive information about settlement dynamics that informs future experiments. To address the second objective, we assessed <i>X. globicipitis</i> prevalence in stranded dolphins from South Carolina and Georgia. Stranding data were examined to determine the prevalence of <i>Xenobalanus</i> on stranded dolphins as a potential indicator of poor health in these sentinel species. We observed higher prevalence of <i>X. globicipitis</i> during the spring and fall months, with the highest occurrence on the trailing edges of the flukes. These data were compared to Dolphin Morbillivirus (DMV) cases from the 2013-2015 Mid-Atlantic Unusual Mortality Event and a significant association between DMV-positive individuals and barnacle presence in South Carolina was observed.