Observations on the life history and feeding ecology of a specialized nudibranch predator (Phyllodesmium poindimiei), with implications for biocontrol of an invasive octocoral (Carijoa riisei) in Hawaii

The azooxanthellate octocoral, Carijoa riisei (Duchassaing and Michelotti, 1860) has spread throughout the Main Hawaiian Islands over the last 40 years proliferating in abundance. Given the rapid proliferation and ecological impact of the octocoral in Hawaii, there is interest in using the aeolid nudibranch Phyllodesmium poindimiei [Risbec, J., 1928. Contribution á l'étude des nudibranches Néo-Calédoniens. Faune des Colonies Francaises 2: 1–328], a specialized predator of Carijoa sp. in southern Australia, as a potential biocontrol agent. Using the nudibranch for biocontrol of C. riisei warrants examination of its life history and effectiveness at controlling its prey. The specialized nature of P. poindimiei predation is confirmed and some of its life history characteristics are described. The aeolid exhibits an approximately annual life cycle, has planktotrophic development and spawns continuously throughout the year, with no evidence of lunar patterns. However, the nudibranch was not successful at controlling C. riisei populations in any experimental feeding trial. Even under high nudibranch densities in aquaria, predation is incomplete, because portions of C. riisei are left unharmed. Additionally, sponge overgrowth suppresses nudibranch predation on the octocoral, and the portunid crab Thalamita integra is identified as a predator of P. poindimiei. Together these factors indicate that biocontrol of C. riisei using P. poindimiei should not be pursued.