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Taxonomic name: Carijoa riisei (Duchassaing & Michelotti, 1860) Synonyms: Common names: Branched pipe coral, orange soft coral, snowflake coral Organism type: coral Carijoa riisei commonly known as "snowflake coral" or "branched pipe coral", is a soft coral species. Originally from the tropical Western Atlantic it was first reported in the Pacific Ocean around the Hawaiian Islands in the 1970's. Its introduction was thought to be benign until recent surveys began showing it proliferating at depths as far down as 120m off the island of Maui, where it is rapidly changing habitat and out-competing native black coral colonies. Description Carijoa riisei is an octocoral that forms erect, branching colonies with flexible stems. Each tall axial polyp has many short lateral polyps. Polyps, when extended, have eight white pinnate tentacles, like the rays of a snowflake, unlike stony corals which have six tentacles. The long stems or branches of the octocoral are a dirty white colour, but they are almost always covered with a very thinly encrusting orange-red sponge, which was identified as Desmapsamma anchorata on Carijoa identified as C. riisei from Indonesia (Cacinai et al. 2004). Two types of sclerites occur in the body wall (HBS, 2002). C. riisei colonies grow about 10-25cm high (Samuel Kahng., pers. comm., 2005). Occurs in: coastland, estuarine habitats, marine habitats Habitat description Carijoa riisei is reported to grow well in turbid waters rich in organic matter and zooplankton on which it feeds. It requires a firm surface on which it attaches using stolons (root-like structures). It also grows well on artificial hard surfaces such as metal, plastic, concrete, etc. It is commonly reported on artificial reefs visited by recreational scuba divers. It is a passive filter feeder and needs moderate amounts of water flow, which is provided by wave surges and tidal or long-shore currents. It does not proliferate in direct sunlight and is usually most abundant on rocky surfaces or other hard substrates at depths below significant light penetration (Kahng, Undated(b)). Grigg (2003) states that not only can this species be found on pier pilings in shallow water, but that it is also abundant in much deeper water (down to 120m), particularly in shaded environments. General impacts Carijoa riisei had been described as a shallow water species, but deep-water surveys conducted near Maui in Hawai‘i discovered C. riisei overgrowing >70% of the black coral colonies (Antipathes dichotoma and A. grandis) in certain areas at depths of 65-115m (Grigg 2003). C. riisei can settle and grow on other stationary organisms like shellfish and coral. When conditions are favourable it is capable of explosive growth, hence able to smother competitors and occupy any available space. C. riisei is a voracious feeder and can consume large quantities of zooplankton (ecological impacts of this feeding habit are yet to be studied) (Kahng, Undated(b)). C. riisei exhibits high fecundity compared to other corals (clonal benthic marine invertebrates like corals in general exhibit much lower fecundity than aclonal benthic marine invertebrates like mussels). No significant predators have of C. riisei have been found in Hawai‘i with the possible exception of a recently discovered introduced nudibranch, Phyllodesmium poindimiei. Predators of Carijoa in other parts of the globe have been reported (Samuel Kahng., pers. comm., 2005). Uses Gasparini et al. (2004) reports that Carijoa riisei is used in the aquarium trade and can also be found in the souvenier trade. Notes While shallow-water octocorals (soft corals) are well described in the Caribbean, their taxonomy in the Indo-Pacific is less well defined. Many genera of soft corals in the Indo-Pacific are not defined to the species level. In Hawai‘i, the Carijoa species was identified as C. riisei by a leading octocoral taxonomist. However, recent molecular sequencing work in progress is now casting doubt on the Caribbean/Atlantic origin for the Hawai‘ian population (Samuel Kahng., pers. comm., 2005). Geographical range Native range: Carijoa riisei occurs naturally in the Western Atlantic and the Caribbean from Florida to Brazil (Bayer, 1961). Known introduced range: Carijoa identified as C. riisei was reported in Hawai‘i in 1972, the conclusion it was introduced is based on its absense from historical records prior to 1972. It has recently been recorded at depths of 100m in Hawai‘i (Grigg, 2003). Reports identifying Pacific Carijoa require genetic verification using DNA analyses, which are currently underway. Introduction pathways to new locations For ornamental purposes: Gasparini et al. (2004) reports that Carijoa riisei is used in the aquarium trade and can also be found in the souvenir trade. Pet/aquarium trade: Gasparini et al. (2004) reports that Carijoa riisei is used in the aquarium trade and can also be found in the souvenir trade. Ship/boat hull fouling: HBS (2002) reports that Carijoa riisei is most likely to be introduced as fouling on ships' hulls. Management information Preventative measures: Carijoa riisei has been described as the most invasive of the 287 non-indigenous marine invertebrates in Hawai’i (Toonen, 2004). Toonen (2004) points out that C. riisei has unique characteristics which aid its dispersal via maritime vectors. Research into its reproductive system and larval development are a primary requirement in the development of an effective management strategy aimed at preventing spread and containing existing populations. A research programme supported by Sea Grant and the Hawai‘i Undersea Research laboratory (HURL) is underway to study the ecological impacts of C. riisei on Hawai‘i's deep water and shallow coral reef communities. Biological: Kahng (Undated(a)) has found that, "A potential agent of C. riisei bio-control (introduced aeolid nudibranch soft coral predator) has recently been identified but must undergo further research before it can be considered as an actual management technique." Nutrition Carijoa riisei lacks symbiotic algae (unlike many stony corals), and is an obligate predator of zooplankton. Octocorals in general have weak nematocysts (stinging cells). From feeding trials in Hawai‘i, C. riisei does not appear to have effective nematocysts (Samuel Kahng., pers. comm.., 2005). Reproduction Carijoa riisei is capable of single parent reproduction and has male, female and hermaphrodite colonies. It also spreads by vegetative growth through runners and stolons which spread and colonise adjacent areas in all directions. C. riisei also exhibits high fecundity, producing almost continously, and hundreds of eggs per axial polyp (Kahng, Undated(a)). HBS (2002) reports that, "Polyps may reproduce asexually by simply splitting in two, or sexually by release and fertilisation of gametes (a cell connected with sexual reproduction, which is either a male sperm or a female egg) into the water column. The resulting planula larvae (flat ciliated free-swimming larva) settle to the bottom and develop directly into young polyps." Reviewed by: Steve. L. Coles, Ph. D. Research Zoologist. Bishop Museum, Department of Natural Science Honolulu, Hawaii USA Sam Kahng Department of Oceanography University of Hawaii at Manoa Honolulu. Hawaii Principal sources: Kahng, Undated(b) Carijoa riisei: Fact Sheet Department of Oceanography, University of Hawai‘i. HBS, 2002 Carijoa riisei (Duchassaing & Michelotti, 1860). Toonen, R. 2004. Reproduction and developmental characteristics of an alien soft coral (Carijoa riisei) in Hawai‘i (FY 2004-2005). Hawai’i Institute of Marine Biology. Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG) To contribute information, please contact Shyama Pagad. Last Modified: Sunday, 23 March 2008