MCCLINTOCK , JB; AMSLER, MO; AMSLER, CD; SOUTHWORTH, KJ; PETRIE, C; BAKER, BJ; Univ. of Alabama at Birmingham; Univ. of Alabama at Birmingham; Univ. of Alabama at Birmingham; University of Alabama at Birmingham; University of South Florida; University of South Florida; ; : Biochemical composition, energy content and chemical antifeedant and antifoulant defenses of the colonial Antarctic ascidian Distaplia cylindrica

The colonial ascidian Distaplia cylindrica occurs in soft substrata in Antarctica. Colonies grow to 7 m height and present considerable materials and energy for predators and surface area for fouling organisms. Nonetheless, in situ observations provided no evidence of predation nor biofouling. Mean energy content was high (14.8 kJ/g dry wt) and mostly attributable to protein (12.7 kJ/g d wt). The sympatric omnivorous sea star Odontaster validus rejected pieces of colonies in feeding assays while readily ingesting alginate food pellets. Deterrence was attributable to defensive chemistry as colonies are nutritionally attractive, lack physical protection, and O. validus display significant feeding deterrent responses to alginate food pellets containing tissue-level concentrations of organic extracts. In addition, high acidity measured on colony surfaces (pH = 1.5) and homogenized whole colony tissues (pH = 2.5) indicate surface-sequestration of inorganic acids. Agar food pellets prepared at tissue levels of acidity caused feeding deterrence in sea stars. Thus, both inorganic acids and secondary metabolites contribute to chemical defenses. Distaplia cylindrica also possesses potent antifoulant secondary metabolites. Tissue-level concentrations of hydrophilic and lipophilic extracts caused high levels of mortality in a sympatric pennate diatom. Chemical defenses may contribute to the abundance of D. cylindrica and thus play a role in energy transfer and community structure in the Antarctic marine benthos. We acknowledge the support of the Office of Polar Programs of the National Science Foundation.