Dive 11: “Ridge” Seamount
July 25, 2017
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Dive 11: Forest of the Weird

While exploring "Ridge" Seamount, Deep Discoverer encountered an alien-like community composed almost exclusively of glass sponges with their concave sides directed towards the current. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2017 Laulima O Ka Moana.. Download larger version (mp4, 40.3 MB).

The bottom was characterized by large boulders, cemented basalt, and rocks with a heavy manganese crust and light dusting of sediment. The dive track going upslope was on a sustained community of sponges that also included deep-sea octocorals and associated invertebrates. When Deep Discoverer reached a ridge, the current changed. Here, the community was composed almost exclusively of glass sponges and their diversity increased dramatically – some hexactinellids were unusually large. Many sponges had their concave sides directed towards the current, and a new sponge species in the genus Poliopogon was observed. Dead glass sponge skeletons were also present, sometimes in high abundance. Colonial octocorals were the second most abundant group observed and included members of the chrysogorgiids, the primnoids, coralliids, and five or six species of bamboo corals – one whip was nearly five meters tall. There were a few black corals, “stoloniferous” zoanthids, and at least two species of anemones – several small individuals covered a primnoid coral. Other notable cnidarians included small hydroids, a small benthic ctenophore on a glass sponge, a four-armed narcomedusae, and a small jellyfish. Relatively few observations of echinoderms were made during this dive and included a single stalked crinoid with hydroids on its stalk, feather stars (one with eulimid snails parasitizing it), Lophaster, a solasterid sea-star, a filter-feeding brisingid, one urchin, and two sea cucumber species. Numerous ophiuroid commensals were present on corals. Other organisms observed included shrimp, squat lobsters, small swimming polychaetes, worms of unknown affinity, and small lyrate-shaped organisms which were not identified. We saw no fish today.