Sixgill shark seen while exploring Santa Rosa Reef, south of Guam, during the first dive of the expedition on April 20, 2016. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas. Download (mp4, 39.7 MB)
Dive 1 was conducted today on a pinnacle located on Santa Rosa Reef, about 30 nautical miles southwest of Guam. We targeted this particular feature because its depth and structure are similar to known habitat for commercially important species of precious corals (typically found between 300-600 meters) and bottomfish (<400 meters), which are both managed by NOAA Fisheries. We began the remotely operated vehicle dive at ~650 meters depth and slowly ascended along the pinnacle slope to survey for both geological and biological features. At the start of the dive, the seafloor had relatively low relief and resembled a field of rocky rubble. As we ascended, there was much more vertical structure, with large boulders mixed in with the smaller broken up rocks. The dominant geologic features transitioned from basaltic to carbonate-rich composition. We made collections of both types of rocks for further analyses following the cruise. We were very surprised to come across a large fossilized shallow-water coral reef. Throughout the dive, we encountered several species of precious corals, confirming their presence in the region. Precious corals imaged included the stunning gold coral Kulamanamana in the family Parazoanthidae, the red precious coral Hemicorallium in the family Corallidae, and several black corals. As we transited shallower, the density of organisms increased, and we encountered relatively abundant assemblages of corals, squat lobsters, echinoderms, and fish. Although we did not encounter any snappers or groupers, we encountered three species of fish that are of commercial value: Monchong (deep-sea pomfret), Alphonsin (genus Beryx), and a roughy (Hoplostethus). A highlight of the dive was a visit by a sixgill shark! We finished the dive at ~350 meters, with all ship and shore-based participants extremely happy with the great success of this first dive of the expedition.