Dive 03: "Te Kawhiti o Maui Potiki"
May 2, 2017
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Dive 03: The Deep Forest

While exploring at a site informally called 'Te Kawhiti' on the northern edge of the Manihiki Plateau, scientists encountered a deep-sea coral forest. The hard seafloor at the site provided an ideal surface on which corals can grow and provide habitat for a range of animals, much like trees do in a forest on land. Video courtesy of the NOAA Office of Ocean Exploration and Research, Mountains in the Deep: Exploring the Central Pacific Basin. Download (mp4, 23.6 MB)

We had a fantastic dive today on a coral forest along a ridge North of the Manihiki Plateau, at a site we are calling "Te Kawhiti o Maui Potiki." Fifty scientists from around the world joined as we explored this interesting ridge. The ridge feature was previously unmapped, and surprisingly reached 1,000 meters (3,280 feet) closer to the ocean surface than indicated by satellite altimetry.

Remotely operated vehicle (ROV) Deep Discoverer (D2) began on the south side of the ridge and worked upslope before following the ridge crest to the summit. From the moment we touched down on the seafloor, we were surrounded by large bamboo coral colonies. The geology showed mostly in-place outcrop. The rocks were dark in color and covered with ferromanganese (Fe-Mn) crust. Light-colored sediments filled in the low topography between the outcropping rocks. Large corals - some as large D2 or larger - colonized almost every surface. For the duration of the transect (to the shallowest part of the feature), we were in a dense bamboo coral (Isididae) forest, with at least many hundreds, if not thousands, of colonies. Several broken branches and dead coral colonies were seen scattered in areas of live colonies. Most live colonies had crinoids perched on branches (possibly three different species), and on several occasions we encountered upright colonies stripped of tissue and completely covered in crinoids. Other associates included overgrowing zoanthids (at least two species), brittle stars (Ophiacanthidae), and gooseneck barnacles. Along some sections of the ROV path, pillow-like structures were evident in the rocks despite the presence of the Fe-Mn crusts on the surface. Other corals observed included: Octocorals, Anthomastus, a rock pen, at least two species of Chrysogorgidae, Paragorgiidae, at least three additional species of bamboo corals, Corallidae, Iridogorgia, and at least four species of black corals. Sponge observations included a possible new species of glass sponge, carnivorous Cladorhizidae, and several species of glass sponges.

Other biological observations included two species of sea anemone, munidopsid crabs, king crabs, shrimp, hermit crabs with gooseneck barnacles, two species of seastars, sea urchin, chirostylid squat lobsters, and a fourth species of crinoid (on the rock substrate) with 10 arms and tips lacking cirri. Many of the crinoids imaged showed predatory snails attached to the arms. Fish were uncommon, but observations included Antimora, rattail, and cusk eel.

Following the benthic exploration, we made a series of midwater transects. This was the first observation of life in the water column that had ever been completed in this area. We spent 10 minutes at eight different depths ranging from 1,800 to 300 meters. Diversity was high, and we saw numerous siphonophores (colonial jellyfish), chaetognaths (arrowworms), larvaceans (sea tadpoles), ctenophores (comb jellies), and jellyfish throughout much of the water column. Some other interesting fauna that we observed included a pelagic sea cucumber, a pelagic tunicate, and a polychaete worm. We saw a surprising number of fishes, including a snipe eel, several bristlemouths, and a hammerjaw.