Plants and animals moved from their native habitats to new locations by humans, either accidentally or intentionally, are considered to be alien or introduced species. When in a new environment, introduced species can compete with native ones for food or space; introduce new pests, parasites, or pathogens; and generally cause a disruption in the native environment. Studies have shown that there are also more than 300 species of plants and animals introduced into coastal marine and estuarine waters in Hawai‘i.
There are two species of introduced invasive invertebrates that we ask to be reported to Eyes of the Reef. they are:
Upside-down Jellyfish (Cassiopea andromeda) is an introduced species sometimes found in large numbers in calm lagoons and harbors.
• Usually lies “upside-down” on bottom
• Yellow-brown with white or pale spots and streaks.
• 12-14 inches in diameter.
• Frilly tentacles, may be mistaken for sea anemones.
Upside-down Jellyfish (Cassiopea spp.) was accidentally introduced to O’ahu, most likely by either hull-fouling or in the ballast water of ships. The jellyfish now occurs in shallow harbors and lagoons, on intertidal sand or mud flats, and around mangroves throughout Hawai‘i. Cassiopea is usually found in calm shallow water, lying on the bottom mouth upwards, gently pulsating its bell to create water flow over its arms. Like corals, the jellyfish has zooxanthellae living in its arms and other tissues on the ventral surface. Lying on the sea floor to provide sunlight to its photosynthetic symbiotic algae, these odd jellyfish are often mistaken for sea anemones.
Cassiopea spp. feed on zooplankton, and in areas where Cassiopea are in large numbers they may monopolize space. The jellyfish is also a nuisance species which can sting people. Depending on an individual’s sensitivity to the toxin of the nematocysts, a sting from Cassiopea may result in skin welts, skin rash, itching, vomiting and skeletal pains.
• Polyps have eight tentacles, compared to six in most stony corals.
• The polyps and branches are white, but branches may appear orange due to encrusting sponge.
• Can settle and grow on other stationary organisms like corals and shellfish.
• Found throughout the main Hawaiian Islands
Snowflake Coral (Carijoa sp.) is an invasive species of octocoral – also referred to as “branched pipe coral”. At this time it is unclear if our Hawaiian species is an alien or native species. First discovered in Hawai‘i in 1966 in Pearl Harbor, it has since spread to all the main Hawaiian Islands. It is often found in fouling communities in shaded areas such as under piers and on shipwrecks. Snowflake Coral threatens Hawai‘i’s biodiversity by monopolizing space resources and by displacing native species. On Maui, in 2001 surveys it was found that it has overgrown and killed over 60% of the black coral trees between 80 and 105 m depth; it now threatens Hawai‘i’s $30 million precious coral industry.
Snowflake Coral can grow very quickly, enabling it to smother competitors. The octocoral reaches maturity very quickly, reproduces year around, and produces hundreds of eggs per polyp which are widely dispersed by ocean currents. In addition to sexual reproduction, Snowflake Coral also spreads asexually, or vegetatively with “runners” . With only one predator in Hawai‘i – a small nudibranch – there are virtually no natural controls for this invasive invertebrate.
For more information about introduced invasive species visit the Bishop Museum’s and University of Hawai‘i’s Introduced Marine Species of Hawai‘i website.