Photographer: Keoki Stender Source: www.marinelifephotography.com Copyright: Keoki Stender (used with permission)
Carijoa riisei is a soft, branching coral that forms carpets by attaching to hard surfaces in marine waters. The cylindrical branches have multiple polyps which have eight white tentacles when extended. Unlike other corals, C. riisei does not have any symbiotic algae and therefore is an obligate predator of zooplankton. Also, C. riisei cannot grow in direct sunlight so this coral flourishes in shaded and deeper waters.
This coral is an ecological threat in two ways, (1) it a voracious predator of zooplankton and (2) its growth can cover other native corals. With C. riisei consuming high levels of zooplankton it is able to out-compete other native corals and invertebrates that survive off of zooplankton. Studies have shown that C.riisei populations can blanket native Black Coral populations and severely reduce the size of the native colonies, especially in deeper waters. By overtaking black corals the snowflake coral is severely changing oceanic ecosystems at depths that are not properly monitored or managed.
This coral is in the Cnidaria clade and has a juvenile planula stage which is free-floating and can attach to any hard surface. This life cycle feature allows C. riisei to be spread by boats. The snowflake coral also has a higher fecundity than other native corals. The continuous reproduction of this coral allows it to “takeover” new habitats. Mature polyps can reproduce asexually or sexually by a release of gametes; the resulting planula larvae settle on the bottom and develop into young polyps.
The snowflake coral was first described off of the US Virgin Islands in 1860 as Clavularia riisei and was thought to be a native coral of the Western Atlantic. Later in 1972, it was discovered in Hawaii at Pearl Harbor. By thinking that C. riisei was native to the Western Atlantic the invasive coral has been able to establish colonies along the coastline of Florida and the Gulf of Mexico for an unknown amount of time.
It wasn’t until 2010 when a phylogenetic survey was performed by collecting specimens of C. riisei off of the coast of each continent (except Europe) and comparing them, that is was realized the snowflake coral is not a native to the Western Atlantic. The study demonstrated that C. riisei is more closely related to a species in the Indo-Pacific region than those in the Western Atlantic. This suggests that the populations in Florida, Puerto Rico, and Brazil are actually invasive populations. However, with an undocumented presence of C. riisei in Hawaii the snowflake coral is, and should be considered as, an invasive species.
U.S. Present: FL, HI, and PR, also found in the Gulf of Mexico
U.S. Habitat: Marine, estuarues, and coastland habitats. Carijoa riisei is known to grow while in turbid waters rich in organic material and requires a firm surface for attachment.
In the native Indo-Pacific region there are two species of nudibranchs that feed on C. riisei: (1) Tritoniopsis elegans, a generalist feeder and does not specifically eat only Snowflake coral, and (2) Pyllodesmium poindimiei, which feeds exclusively on C. riisei and will even starve in the absence of the snowflake coral. Unfortunately, these nudibranchs are endemic to the Indo-Pacific waters and can only manage C. riisei populations in Hawaii.
Unfortunately, this coral is still actively sold online and offline for the aquarium trade and the souvenir trade. So until it is found illegal to sell C. riisei, this coral will continue to spread in to Atlantic waters and the Gulf of Mexico.
Concepcion, G. T., Kahng, S. E., Crepeau, M. W., Franklin, E. C., Coles, S. L., & Toonen, R. J. 2010. Resolving natural ranges and marine invasions in a globally distributed octocoral (genus Carijoa). Mar Ecol Prog Ser, 401:113-127.
Godwin LS 2003. Hull fouling of maritime vessels as a pathway for marine species invasions to the Hawaiian Islands. Biofouling 19:123–131.
Grigg RW. 1965. Ecological studies of black coral in Hawaii. Pac Sci 19:244–260.