Carijoa riisei

Carijoa riisei, the snowflake coral or branched pipe coral, is a species of soft coral in the family Clavulariidae. It is native to the tropical western Atlantic Ocean and has spread to other areas of the world such as Hawaii, where it is regarded as an invasive species.

Carijoa riisei
Scientific classification
Kingdom: Animalia
Phylum: Cnidaria
Class: Anthozoa
Order: Alcyonacea
Family: Clavulariidae
Genus: Carijoa
Species:
C. riisei
Binomial name
Carijoa riisei
(Duchassaing & Michelotti, 1860)[1]

Description

Carijoa riisei is a colonial soft coral with a tangled, bushy growth form. It has hollow branches that may be 30 cm (12 in) long, growing from a creeping stolon. The branches grow by budding off the stolon and have eight longitudinal furrows and a prominent polyp at the tip. The calyces in which the polyps sit are tubular, widely separated on the branches, 3 to 5 mm (0.12 to 0.20 in) long and 1.5 mm (0.06 in) wide. The polyps are retractible into the branches.[2]

Distribution and habitat

Carijoa riisei is native to the tropical and semi-tropical western Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico. Its range extends from South Carolina to Brazil. It was first detected in Hawaii in 1972 when it appeared in Pearl Harbor. Since then it has spread to the other islands in the archipelago. It has also been detected on other Pacific islands, and on the coasts of Australia and Asia. It is a shade-loving species and grows on hard surfaces away from direct sunlight. These include caves, overhangs, ledges and under piers. It is a fouling organism and will grow on metal, wood, concrete, plastic and rope. It thrives in turbid water with moderate to strong currents or wave action.[3]

Biology

Carijoa riisei is an azooxanthellate species. This means that its tissues do not contain the symbiotic single-celled protists known as zooxanthellae to provide it with energy, as most species of coral do. Instead it needs to catch all its food by extending its polyps and expanding its tentacles. It thrives in turbid waters with moderate to strong movement which brings plenty of zooplankton and other food particles within its reach on which to filter feed.[4]

Individual colonies of C. riisei are either male or female. Gametes are liberated into the sea at any time of year, a strategy unusual among corals which mostly synchronise spawning with the phases of the moon. The eggs tend to sink which may mean the larvae are benthic rather than planktonic.[5]

Invasiveness

In Hawaii, at depths below about 75 m (246 ft), the invasive Carijoa riisei overgrows and kills the native black corals Antipathes dichotoma and Antipathes grandis. These are slow-growing stony corals with black skeletons, which are used for the manufacture of jewelry and are the subject of a managed fishery. The ecological balance is disturbed as the black corals are smothered by the faster growing octocoral and fail to reach a reproductive age (twelve years). The rapid spread of C. riisei in Hawaii may have been facilitated by the relative scarcity of native octocorals, a group that dominates many reef systems in the Caribbean and the Indo-West Pacific.[4]

The nudibranch Phyllodesmium poindimiei feeds on C. riisei,[6] but it cannot be used in Hawaii as a biocontrol because, even under ideal conditions, the octocoral can grow faster than the nudibranch can destroy its tissues.[6] The only other predators so far identified are the nudibranch Tritoniopsis elegans and the bearded fireworm Hermodice carunculata.[7]

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References
  1. van Ofwegen, Leen (2014). "Carijoa riisei (Duchassaing & Michelotti, 1860)". WoRMS. World Register of Marine Species. Retrieved 2015-03-21.
  2. Reed, John. "Carijoa riisei (Duchassaing & Michelotti, 1860) Clavulariidae". South Florida Octocorals. Retrieved 2015-03-21.
  3. Kahng, Sam. "Snowflake coral (Carijoa riisei)" (PDF). Global Invasive Species Database. Retrieved 2015-03-22.
  4. Kahng, Samuel E.; Grigg, Richard W. (2005). "Impact of an alien octocoral, Carijoa riisei, on black corals in Hawaii". Coral Reefs. 22 (4): 556–562. doi:10.1007/s00338-005-0026-0.
  5. Kahng, Samuel E.; Benayahu, Yehuda; Wagner, Daniel; Rothe, Nina (2008). "Sexual reproduction in the invasive octocoral Carijoa riisei in Hawaii". Bulletin of Marine Science. 82 (1): 1–17.
  6. Wagner, D.; Kahng, S. E.; Toonen, R. J. (2009). "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". Journal of Experimental Marine Biology and Ecology 372(1-2): 64-74. doi:10.1016/j.jembe.2009.02.007. PDF Archived 2010-12-24 at the Wayback Machine.
  7. Souza, J. R. B.; Rodrigues, H. A.; Neves, B. M.; Perez, C. D. (2007). "First report of bristleworm predator of the reef octocoral Carijoa riisei". Coral Reefs. 26 (4): 1033. doi:10.1007/s00338-007-0290-2.
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