Dive 06: "Keli'ihananui"
May 6, 2017
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Dive 06: Midwater Journey

On May 6, after finishing exploration of the seafloor, we conducted a series of midwater transects from 1,400 to 300 meters (~4,595 to 985 feet). These transects increase our knowledge about the largest, yet one of the least understood, biomes on Earth. The dive took place in the Jarvis Unit of the Pacific Remote Islands Marine National Monument, which is one of the few units of the monument where the water column is protected in addition to the seafloor. Video courtesy of the NOAA Office of Ocean Exploration and Research, Mountains in the Deep: Exploring the Central Pacific Basin. Download (mp4, 24.9 MB)

Dive 06 was conducted on a seamount dubbed "Keli'ihananui." This seamount was previously mapped in January 2017 on another NOAA Ship Okeanos Explorer expedition. The seafloor was covered in soft sediment intermingled with outcrops of ferro-manganese (Fe-Mn) encrusted rocks. Because many animals in the deep ocean attach to hard substrate, we saw more animals on or near the rocks than we observed in the sediment. Observations included a pycnogonid (sea spider), anemone, holothurians (sea cucumbers), urchins, a few different octocorals, sea stars, ophiuroids, aplacophorans (a shell-less, benthic, worm-shaped mollusc), crinoids, sponges, a carnivorous sea squirt, shrimp, a gastropod, and a few different fish. Some sponges had attached themselves to the rocks in an unusual manner we had not previously seen: they had several leg-like stalks.

After completing the benthic exploration, we conducted a series of midwater transects from 1,400 to 300 meters (~4,595 to 985 feet). These transects increase our knowledge about one of the least understood biomes on Earth. Fauna observed while surveying the water column were diverse and included: pelagothurian (pelagic sea cucumber), numerous jellyfish species, chaetognaths (arrow worms), midwater fish, ctenophores (comb jellyfish), and multiple species of siphonophores (colonial jellyfish). We were especially excited to see a pyrosome (a colonial tunicate that is long and hollow) that was several meters long – this is a relative of the benthic carnivorous sea squirt we saw.