Ecology and ecological impact of an alien octocoral, Carijoa riisei, in Hawai'i

Of 287 alien marine invertebrates in Hawaii, Carijoa riisei is the most invasive. Since its discovery, C. riisei has proliferated throughout the Main Hawaiian Islands and been observed overgrowing corals at depth in the Au'au Channel. The biogeography and phylogeography of Carijoa were investgated to determine the origin and dispersal history of C. riisei in Hawaii. The biology, ecology and ecological impact of C. riisei were investigated to understand the mechanisms underlying its ecological success.; Originally described from the Caribbean, C. riisei in Hawaii was pressumed to be a Caribbean introduction. However, genetic analysis suggests Carijoa species are native to the Indo-Pacific. Carijoa in Hawaii was likely introduced multiple times from the Indo-Pacific and consists of C. riisei and at least one additional congener.; C. riisei's ecological success is due to a combination of species and habitat specific attributes, and a "key-lock fit" between C. riisei and Hawaii. C. riisei's fast growth and vegetative reproduction enable it to attain high density and out compete and overgrow native benthic fauna. C. riisei's early maturity, high fecundity, and continuous breeding facilitate fast population growth and local dispersal. C. riisei's resilience and broad ecological flexibility enable it to colonize and persist in very different habitats. In Hawaii, C. riisei is not limited by food, space, competition, or predators which result in low mortality and dominance of climax communities.; Hawaii's under-utilized niche of large, sessile suspension feeders, low biodiversity, and taxonomic isolation relative to shallow-water octocorals contribute to its susceptibility to C. riisei. Life history traits which enable C. riisei to exploit maritime vessels as a dispersal mechanism are largely unique among corals and help explain why other ecologically dominant coral species have not yet invaded Hawaii.; Despite being relatively free from anthropogenic disturbance, the deep coral reef ecosystem in Hawaii is being severely impacted by the invasion of C. riisei. In the Au'au Channel, over 50% of black corals between 70-110 m are overgrown by C. riisei. Evidence suggests that this biological invasion continues to progress. For a coral reef ecosystem, the scale and ecological impact of this alien invasion are unprecedented.