Dive 06: Winslow Reef Complex
March 14, 2017
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Dive 6: Deepwater Siphonophore

On March 14, during the sixth dive of the expedition, this intact deepwater siphonophore was observed. Although they may appear to be a single organism, these giant siphonophores are actually comprised of a colony of individual hydrozoans, each specialized for different functions such as swimming, feeding, and reproduction. Video courtesy of the NOAA Office of Ocean Exploration and Research, Discovering the Deep: Exploring Remote Pacific MPAs. Download (mp4, 20.0 MB)

Dive 06 began at 1,560 meters on an unnamed seamount west of Winslow Reef complex, within the United State's Exclusive Economic Zone. Moving upslope along sediment channels, scientists observed several fish, including cusk eels, brotula, slickhead, and a cutthroat eel (possibly a gravid female). Other species encountered included several large bamboo colonies attached to boulders, large sponges, octocorals, xenophyophores, and a seastar. As the dive transitioned to a sedimented gradual slope, typical sediment dwellers were observed: sea pens, urchins, sea cucumbers, sea spider, spiny eels, and tripod fish. The final segment of the dive was characterized by sedimented ledges punctuated by high profile rocks and large boulders. Additional fauna encountered on this heterogeneous terrain included different bamboo species including the whip with an amphipod associate and a collected branched form, zooanthids growing on a dead bamboo skeleton, black coral whips, encrusting sponges, and a sea star. Additional fishes included a male halosaur, unknown cusk eels, and cutthroat eels. There were several dead bamboo skeletons and bases scattered throughout the beginning and end of this dive. One base attached to manganese crust was collected to estimate the coral age. Also observed throughout the dive was an unknown yellow bamboo coral collected for identification. At approximately 1,366 meters the summit had exposed rock interspersed with patches of sediment and the largest bamboo colonies attached to the rocks with crinoids and several squat lobsters. On a topographic high, scientists found a very large, green-blue plexaurid coral with several associates (crinoids and brittle stars). Because of the uncertainty about the family-level identification of this coral, a piece was collected with associates. A new sea star was observed at the base of this colony. This dive was characterized by relatively high densities of one species of branched bamboo, with remarkably large colonies occurring at the summit. Given their size and likely old age, there may be long-term environmental stability at this seamount, including adequate food supply, sufficient currents, and minimal direct human impact. However, the large density of dead bamboo bases and rock debris fields down slope may indicate periodic disturbance events, including landslides.