Dive 02: Horizon Guyot
July 13, 2017
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Dive 02: Glass Animals

While exploring Horizon Guyot, a seamount located north of Johnston Atoll, scientists observed a seafloor community dominated by several species of hexactinellid – or glass – sponges. Glass sponges have skeletons made of silica, which is the same material used to make glass; however, glass sponges are not glass, per se. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2017 Laulima O Ka Moana.. Download larger version (mp4, 31.5 MB).

Horizon Guyot is a manganese-encrusted seamount located north of Johnston Atoll. This site was selected to gain a better understanding of manganese-crust communities. After a delayed start due to a dynamic positioning system issue, Deep Discoverer (D2) arrived on the seafloor at 1,930 meters (~6,330 feet). The substrate was mixed rock consisting primarily of manganese-covered boulders and cobbles with a predominantly thin layer of sediment. The general topography was relatively flat with a community dominated by several species of hexactinellid sponges, many with associates including brittle stars, small squat lobsters, and hydroids. Feather stars were present on the tops of several standing dead or inert glass sponge stalks. Several octocorals and black corals were present in lower abundance, including bamboo corals, primnoids, “mushroom” soft corals, cup corals, chrysogorgiids, and a stoloniferan. Stalked crinoids and ophiuroids were also observed as commensals on both octocorals and glass sponges, and a very large ophiurid was seen on a sandy bottom. Other observations included a spatangoid urchin on a large sediment bed; a synallactid sea cucumber; two freyellid brisingid sea stars on dead sponge stalks; and one fish – a rarely observed cutthroat eel in the family Synaphobranchidae.