Coral gardens in the dark depths

Date: February 23, 2005

Three different types of corals live in the deep sea – soft, stony or black. Soft corals (or octocorals) often look like colorful undersea gardens of pink, red, and white. They grow in many different forms, including branching sea fans. From a distance they look like bushes or trees, sometimes reaching 2 meters tall.

By measuring radioactive isotopes (with known half-lives) in their skeletons, scientists have calculated that some large colonies of the soft corals Paragorgia and Primnoa appear to be at least 500 years old. Stony corals’ skeletons are dense and rocky and can form extensive mounds, reaching 12 kilometers in length and protruding as far as 30 meters above the seafloor. Reefs of stony corals Lophelia and Oculina are estimated to be more than 1,000 years old. Radiometric dating also indicates that the corals grow very slowly. The third type, black corals (antipatharians) are usually orange to tan in color, but secrete a hard black proteinaceous skeleton. Fishermen once avoided areas with deep-sea corals because they damaged their nets. Now, redesigned trawls and new techniques for removing corals enable fishermen to take advantage of these highly productive locales. But recent damage to deep-sea coral ecosystems and declines in fish stocks have led conservation groups to call for a ban on fishing in areas with deep corals and the establishment of marine protected areas in these places. Find out why deep-sea corals can be compared to ancient forests, where they live, the creatures they shelter, what they eat, what they look like, and how scientists are studying them in order to understand and predict how they will respond to and recover from disturbances such as deep sea bottom trawling. Read the full article by Senior Scientist Lauren S. Mullineaux and Research Associate Susan W. Mills from Woods Hole Oceanographic Institute, Volume 43 No.2 Oceanus. Visit
Oceana’s Pacific Deep Sea Corals
for more deep sea coral images.

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