One of the priority objectives for Dive 6 was to document and better understand fish habitat. While transiting up the ridge at Supply Reef, ROV Deep Discoverer encountered a small aggregation of groupers, a commercially important fish.

One of the priority objectives for Dive 6 was to document and better understand fish habitat. While transiting up the ridge at Supply Reef, ROV Deep Discoverer encountered a small aggregation of groupers, a commercially important fish. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas. Download larger version (jpg, 1.2 MB).

Dive 6: Supply Reef
20.15°N, 145.1°E, 370 meters
June 23, 2016
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Swimming Moray Eel

This moray eel, which measured about 80 centimeters (2.6 feet) long, was seen during Dive 6 of the third leg of the expedition, as we explored a ridge on Supply Reef, an active submarine volcano within the Marianas Trench Marine National Monument. The chimney mounds at Chammoro were small (one to two meters high), but a temperature measurement taken at one chimney was as high as 31.14°C. The dominant fauna throughout the dive was stylasterid corals (a type of hydrocoral) and animals known to be found in common association with vents, such as the Alvinoconcha snails and alvinocaridid shrimp seen in the video. Other fauna documented during the dive included unusual amphipods, rare blind (polychelid) lobsters, two species of unidentified demosponges, cutthroat eels and rattails, and a variety of fish swimming near the vents. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas. Download (mp4, 96.4 MB)

During Dive 6, we explored a ridge on Supply Reef, an active submarine volcano within the Marianas Trench Marine National Monument with confirmed eruptions in 1969 and 1989. The main objective of the dive was to examine and sample young volcanic rocks in order to determine if they are pillow lavas, massive lava flows, or volcaniclastics and to characterize the fauna existing on the shallow flanks of an active volcano. Two types of rock were observed: dark gray, coarse-grained layered sections of volcaniclastics and a very fine-grained, brown ash. The dominant fauna in this area was large lithistid sponges. As remotely operated vehicle Deep Discoverer (D2) transited up slope along the ridge, the seafloor was generally covered with consolidated, layered brown that was sometimes broken into slabs. The shallowest part of the ridge the slope was covered with loose rubble, and increasingly large boulders. Biologic observations throughout the dive included several different species of smaller demosponges that were plentiful throughout, sea stars, sea cucumbers, anemones, urchins, barnacles, squat lobsters, a benthic ctenophore, crinoids, nudibranchs, and small coral colonies. Fish observed included silver tip sharks, onaga, at least two species of moray eels, flounder, a tuna, scorpion fish, and a small aggregation of grouper. D2 also encountered three sea stars (Rhipidaster sp.) that have never before been seen alive.