Dive 04: Johnston Atoll Dive
July 15, 2017
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Dive 04: Battle for Survival

An octocoral and zooanthids compete for space, in a battle to survive in the deep ocean. Seen during Dive 04 to explore along Johnston Atoll at a depth of 600 meters (~1,970 feet). Video courtesy of the NOAA Office of Ocean Exploration and Research, 2017 Laulima O Ka Moana.. Download larger version (mp4, 17.1 MB).

NOAA Ship Okeanos Explorer deployed remotely operated vehicle Deep Discoverer (D2) to a depth of 600 meters (~1,970 feet) where numerous black coral, yellow Acanthogorgia, and Metallogorgia colonies were observed. Cup corals (single polyp scleractinians) were also seen that persisted throughout the dive. Shortly after leaving the landing site, D2 encountered karstic rock formations in an area of high currents. Colonial cnidarians dominated this area. Most importantly, we observed the precious coral Hemicorallium, one of the dive’s primary objectives. First encountered in low abundance, these corals increased significantly when D2 was in an area with high currents and large carbonate blocks; some colonies were large, approximately one meter across. Further upslope, the community transitioned to mostly scleractinian coral, including some “graveyards” – dead coral skeletons that had fallen to the bottom of the slope. In an area with significant current flow, the substrate was covered with several different octocorals, antipatharians, and sponges. Several sea stars were present, including pentagonal “cookie stars” and a new record of a rarely seen Gilbertaster anacanthus. We also observed the goniasterid Circeaster pullus, a known corallivore feeding on the precious coral Hemicorallum for the first time. On two occasions, we observed large blocks with one side covered by glass sponges and the other covered colonies Acanthogorgia colonies. Also observed were two unusual communities of highly abundant and dense micro-invertebrates, one dominated by thin tube-like projections with a “fuzzy” appearance and another by tiny, white zoanthids. Crustaceans included a brachyuran inachid crab with extremely long legs and claws, hermit crabs with sea anemones instead of shells, and small xanthid crabs. Two other unusual invertebrate groups observed included a benthic ctenophore and numerous small white lamp shells with longitudinal notches along each valve. Various fishes were also documented: a ray, deep water cardinal fishes, scorpion fish, channeled rockfish, a few basslets, a spike fish, and two observations of a commercially valuable snapper.