BLACK CORAL IN THE HAWAIIAN ISLANDS AS HARD SUBSTRATE FOR BRYOZOA

During collections in shallow water Hawaiian Island habitats many bryozoan colonies were found on tree-like colonies of black coral, identified as Antipathes dichotoma. The Au Au Channel, between Lahaina, Maui and Lanai Island, slopes SE from about 40 m toward Kealaikahiki Channel which deepens to about 300+ m, trending SW. Extensive beds of black coral, which were considered rare in Hawaii had been discovered off Lahaina by commercial Scuba divers at 50-100 m depths. Colonies were harvested for the jewelry trade by wrapping an anchor chain around the bases and yanking them from the substrate. Trees contained numerous small invertebrates: crustaceans, tunicates, sponges, molluscs, polycheates and some 50 species of bryozoan anascines, ascophorines and cyclostomatids. The black coral hosts one of the most diverse and productive faunas for an invertebrate ecosystem found in the Islands. Tree ages were estimated by ‘growth’ rings to be up to 200 years old; and the black coral provided virtually the only hard substrate available on the steep channel slopes.. Black coral is surprisingly hard, making a good substrate for byrozoan colonies that would remain attached to branches should they be broken off and deposited in sediments at the bottom of the canyons.. The fossil record is scant in the Hawaiian Islands but Pleistocene coral beds are known from terraces on Oahu (Easton, pers. comm). If black coral were present and degraded faster than some heavily calcified bryozoans, the fossil bryozoan distribution patterns could be puzzling. Black coral larvae are apparently carried up the slopes from deeper, older, black coral colonies Shallower beds recovered after reduced harvest pressure due to importation of softer, cheaper, black coral from the Philippines. The habitat will remain if harvesting is maintained at a sustainable level and deeper water harvesting by submersible, which is threatened, does not develop.