Localized induction of a generalized response against multiple biotic agents in Caribbean sea fans

Although inducible defenses are an important component of the defense systems of a range of modular organisms, little is known about inducible defenses of octocorals. A localized inducible response against multiple enemies was detected in the Caribbean sea fans Gorgonia ventalina L. and G. flabellum L. Field surveys showed that localized purpling, resulting from an increase in the proportion of purple sclerites, was associated with overgrowth by Millepora alcicornis and macroalgae, and infection by the fungus Aspergillus sydowii. To confirm inducibility and to assess specificity of the response, a range of treatments--abrasion, cable tie, M. alcicornis, sea fan tissue infected with A. sydowii (diseased allografts), and healthy allografts--was applied to healthy sea fans. After 10 days, all biotic treatments induced a localized physical response consisting of changes in concentration, type, and color of sclerites; however, antifungal activity of non-polar chemical extracts was unaffected. The purpling response appears to be specific to biotic agents and reduces tissue damage in subsequent interactions.[PUBLICATION ABSTRACT]