This high density coral community, with several large basket stars, was documented at the start of Dive 3. At least 50 coral colonies can be seen in this single image.

This high-density coral community, with several large basket stars, was documented at the start of Dive 3. At least 50 coral colonies can be seen in this single image. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas. Download larger version (jpg, 1.1 MB).

Dive 3: Maug
20.05345 N, 145.23010 E, 470 meters
June 20, 2016
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Spider Crab

During Dive 3 at Maug, remotely operated vehicle Deep Discoverer documented an exciting interaction between two crabs, including a unique-looking spider crab. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas. Download (mp4, 106.0 MB)

Dive 3 was the first-ever exploration of the outer edge of the Maug cone. The dive was conducted on a small ridge feature northeast of the crater to survey precious coral, commercially important bottom fish habitats, and fauna in the water column surrounding this island. The dive started at a depth of 470 meters in a very productive area with an abundance of fish, crinoids, sea stars, a diversity of corals, and other organisms. As remotely operated vehicle Deep Discoverer surveyed the edge of the ridge, likely a side vent from the Maug volcano, volcaniclastics of varying sizes and graded bedding in the steep inner wall of the vent were documented. Biology highlights during today's dive included: several different species of bamboo corals; a sponge that has never been reported in the Pacific; an abundance and diversity of echinoderms - basket stars, crinoids, and sea stars; a deepwater sand tiger; slit shells; thousands of small knobby lithistid sponges; and the bright yellow, pseudocolonial coral (Eguchisammia serpentine) which was very common at the shallower depths. We also documented the "gold coral" Kulamanamana haumeaae (a precious coral species). As Kulamanamana can live for thousands of years, these could easily be hundreds of years old. The biggest challenge today was deciding which biological samples to collect: there were so many new and different organisms. At the conclusion of the benthic exploration, we completed a long midwater transect to target the deep scattering layer observed in our EK60 sonars. We observed salps, siphonophores, shrimp, chaetognaths, and ctenophores, as well as what appears to have been an interesting avoidance behavior of the scattering layer.