Megafauna associations with deepwater corals (Primnoa spp.) in the Gulf of Alaska

Few in situ observations have been made of deepwater corals and, therefore, little is known about their biology or ecological significance. Deepwater corals (Primnoa spp.) were observed from a manned submersible at 11 sites in the Gulf of Alaska from 1989 to 1997 at depths of 161-365 m. We identified 10 megafaunal groups that associate with Primnoa to feed on the coral, use the coral branches for suspension feeding, or for protection. Predators on Primnoa polyps included sea stars, nudibranchs, and snails. Sea stars were the main predators, consuming 45% and 34% of the polyps at two sites. Suspension-feeders included crinoids, basket stars, anemones, and sponges. Most suspension-feeders observed at depths >300 m were associated with Primnoa. Protection seekers included rockfish, crab, and shrimp. Six rockfish species were either beneath, among, or above Primnoa. Shrimp were among the polyps, and a pair of mating king crabs were beneath Primnoa. These observations indicate Primnoa are important components of the deepwater ecosystem and removal of these slow-growing corals could cause long-term changes in associated megafauna.