Dive 15: New Seamount 8 Cone
July 29, 2017
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Dive 15: A Year-long Meal

This sea star, likely Evoplosoma sp., was seen eating its way up a coral on a ridge at 2,006 meters (6,851 feet) depth. These large sea stars are one of the most common predators of corals that we see. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2017 Laulima O Ka Moana.. Download larger version (mp4, 29.4 MB).

Starting at a depth at 2,006 meters (6,851 feet), the final dive of the expedition began along the northern side of the cone and proceeded to the top. The hard bottom was composed of heavily consolidated manganese crust with some sediment pockets. The most abundant fauna observed were colonial octocorals, specifically bamboo corals. Additional octocorals observed included chrysogorgiids, primnoids, coraliids, anthothelids, paragorgiids (some whose skeletons were being overgrown by a yellow zoanthid colony), mushroom corals, and rock pens. Other cnidarians included hydroids, sea anemones, a cup coral, and several black corals. Glass sponges were the second most abundant group of animals. The most commonly encountered species was in the genus Walteria; some of these were observed with commensals, such as large isopods, shrimps, and ophiuroids. Other glass sponges included Bolosoma, Caulophacus, Dictyaulus, Poliopogon, Regadrella, and Stelodoryx. The top of the cone was revealed to host a relatively abundant community of bamboo corals, whose numbers had been gradually increasing as we ascended up the cone. Sea stars, including the rarely seen seven-armed Asthenactis sp. and several large-sized coral predators in the genus Evoplosoma, were the most noteworthy echinoderms observed during this dive. Upon reaching the top of the cone, many sea stars were observed feeding on bamboo corals. Sea urchins were only encountered at the peak and sea cucumbers were uncommon. A stalked crinoid and at least two species of feather stars, often present as commensals on corals, sponges, and rocks, were observed. Brittle stars were other common commensals. Although many small snails were observed throughout the dive, the most notable were tiny vermiform mollusks predating on bamboo corals. The numerous smaller crustaceans included squat lobsters and shrimp. Moderately sized isopods were observed living on glass sponges, as well as one living as a parasite on a large grenadier. Several arrow worms were present, as was a single swimming ribbon worm. The many fishes included grenadiers, cusk eels, cutthroat eels, and an unusual anglerfish.