Black coral at 180 feet in the Au'au Channel, Maui Hawaii. Of the more than 200 black coral species, Hawaii has more than 15. Although found at all depths, black corals can be a dominant feature of Hawaii’s unique deep coral reef environment. Click image for larger view and image credit.
Black coral at 210 feet South Kona Hawaii. Click image for larger view and image credit.
Black Corals Of Hawaii
Anthony Montgomery
Hawaii Department of Land and Natural Resources
Division of Aquatic Resources
Black corals are a group of corals that belong to the Order Antipatharia. These corals can be found all over the world at all depths. However, they are typically known as deep-sea corals and can be very abundant in certain areas. Black corals are rarely black, but rather vary in color from white, red, green, yellow, or brown. They can also range in shape from small bushes to bottle brushes to fans to single stalks. Black corals are very different from stony corals in their skeleton. All black corals have a skeleton made of protein and chitin (chitin is the same material as an insect skeleton). In addition, black corals do not have symbiotic algae (zooxanthellae?) associated with them and do not require light, therefore allowing them to extend into depths where light is not present.
Of the more than 200 black coral species, Hawaii has more than 15. Although found at all depths, black corals can be a dominant feature of Hawaii’s unique deep coral reef environment. Particularly, black corals are very common in the Au’au Channel, between Maui and Lanai. This area is extremely unique as it has a high abundance of black coral habitat and as been the basis of a coral fishery for almost 50 years.
Black coral has been historically harvested for manufacturing jewelry. The skeleton can be polished into a very high luster making beautiful jewelry pieces. Hawaiians also use to harvest black coral for medicinal purposes.
Black coral at 210 feet Makahuena Point, Kauai Hawaii. Click image for larger view and image credit.
Black coral at 210 feet in the Au'au Channel, Maui Hawaii. Click image for larger view and image credit.
The Hawaiian black coral fishery began in the late 1950s and has been active since this time. In 1998, surveys showed the Maui black coral population to be sustainable over the previous 23 years. However surveys since this time have shown that the Maui population is undergoing change. The change has consisted of two major impacts on the population. One change has been the discovery of an invasion of an alien soft coral, Snowflake Coral, on the deeper portion of the population. A large percentage of black coral colonies below 240 feet have been overgrown by the alien Snowflake Coral. The second change has been the reduction of larger colonies above 240 feet (greater than 4 feet in height) due to fishing pressure. Both of these impacts are believed to be contributing to a reduction of juveniles into the population. A reduction of juveniles brings into question the future sustainability of the Maui black coral population.
Previous surveys have largely been done using deep mix gas scuba to assess the population. Although this method can generate the correct type of information to assess the population, it requires people to enter the water and collect population information by hand. This type of methodology, although highly effective, is limited by the amount of time a person can spend on the bottom. To help with this limitation, resource managers are interested in looking at new technologies to scan black coral habitat in order to determine the number and size of colonies in a large area.
This project will test laser line scan technology in order to measure and count colonies on the ocean bottom. If this technology is effective in gather the proper information, resources managers will be able to use multiple tools to accessible the future viability of the black coral fishery.
