Native Dictyosphaeria carvernosa overgrowing Kaneohe Bay.

Common native species of algae and invertebrates may bloom out of control when exposed to changing environmental conditions. Invasive species are opportunistic, responding to increased nutrients, changes in sedimentation, salinity or water temperature, or a decrease in predators. These species out-compete, overgrow, and replace coral reef habitats, resulting in reduced light availability to bottom communities, lower productivity, and decrease in biodiversity. The final result can vary from a seasonal bloom that occurs infrequently and irregularly as “pulses” in environmental conditions encourage growth, to a permanent change in the ecosystem in response to permanent changes in coastal waters. Though some blooms may have natural causes, in most cases they are indicative of an underlying environmental problem. As these changes may indicate a changing and stressed reef, we ask that any substantial blooms be reported to Eyes of the Reef.

Identifying Features

• Unusual organism that appears to be spreading quickly
• Stressed or overgrown corals
• Change in biodiversity
• Change in water quality, clarity

Examples of the good gone bad…..

Blooms of native species are often site specific: different species bloom in different locations. The most widely known blooms are usually algae, but invertebrates are also capable of blooming. Invertebrate octocorals and zoanthids have symbiotic algae that provide nourishment in their tissues. Like all algae, these can also respond to increased nutrients and light, enabling the host organism to grow and reproduce more quickly, blooming under the right conditions. Some examples of native species blooms include:

Cladophora sericea on Maui

Cladophora sericea is native to Hawai‘i and is found on most reefs. This green alga is usually part of the highly competitive intertidal community. Approximately 15 years ago the alga became exceedingly abundant on leeward reefs in Maui and large blooms have occurred irregularly, largely due to upland injection wells. During the blooms, large masses of the alga drift in the water column, snagging on coral and rocks, smothering organisms beneath. Rotting algae on the beaches and extensive amounts of algae drifting in the near shore environment prevent people from enjoying ocean-related activities.

Leptolyngbya crosbyana overgrowing finger corals

Leptolynbya crosbyana, a native cyanobacteria or “blue-green” algae, normally appears as small cushions a few inches wide attached to rocks or the tips of coral. In 2008, this alga bloomed in Honaunau Bay, overgrowing coral and forming large, thick mats. Studies are being done to determine why this alga became so aggressive, but nutrient or pollution sources from land are suspected.

Octocorals have been exhibiting blooming tendencies by overgrowing and smothering corals. (in this picture: Sarcothelia edmondsoni)

There are 11 known species of octocorals in Hawai‘i, including the invasive Snowflake Coral. Octocorals are common, shallow water colonies of eight-tentacled polyps without a internal skeleton. Many protect themselves with toxic chemicals. Octocorals exhibiting blooming tendencies have been recorded on the Kona coast of Hawai‘i Island, including the common Sarcothelia edmondsoni, or blue octocoral.

Crown-of-Thorns Seastar (Acanthaster planci)

Crown-of-Thorns (COTS) are a native, coral-eating sea star that can grow almost a meter in diameter.  They have up to 19 arms and the entire upper surface is covered with sharp venomous spines. They are common on Hawai‘i’s reefs and, as a predator, help increase biodiversity on our reefs.  However, in disturbed environmental conditions, they can bloom to unmanageable numbers that can be especially devastating to coral populations.  Eyes of the Reef asks that any observations of 25 or more COTS on a reef be reported.  To learn more about this fascinating animal, visit the COTS information page.