Dive 5: A Peek at Polyps
Many of the deep corals that we see, including octocorals and some hexacorals, are made up of colonies of individual polyps that work together to survive. This video offers a look at some of the colonial coral polyps that we encountered while exploring Polo Seamount on March 13, 2017. Video courtesy of the NOAA Office of Ocean Exploration and Research, Discovering the Deep: Exploring Remote Pacific MPAs. Download (mp4, 17.7 MB)
This dive was on Polo Seamount in the Tokelau Seamount Chain and was the third dive within the Phoenix Islands Protected Area. This was the deepest dive to date, starting at 2,134 meters within a sedimented canyon-like feature and transiting up a low-grade slope to 1,834 meters. Similar to Carondelet Reef (Dive 03) and the unnamed seamount (Dive 04), there was a fair amount of particulate organic matter in the water column on descent. Along the sedimented seafloor, scientists observed sea urchins, cup corals, xenophyophores, shrimp, sea cucumbers, two tripod fish, a brotula, two rattails, a sea star, and a sea pen with a purple polychaete. Large boulders were encountered with several attached fauna: corallimorpharian (looks like an anemone), black coral, crinoid, and tunicates with polychaete and anemone associates. At approximately 2,100 meters, the seafloor transitioned to steep exposed rock encrusted with manganese iron oxide. As Deep Discoverer progressed up the rock face, additional corals were added to the observation list: bamboo corals (branching and whip forms), coralliids (precious coral family), octocorals, primnoids, and black corals. Other invertebrates observed along the steep slope included coral associates (barnacles, sea lilies, zoanthids, squat lobsters, and amphipods), stalked sea lilies, tunicates, sea cucumbers, sea stars, anemones, and sponges. Almost every vertical rock face from 2,002 to 1,837 meters was covered with high densities of corals, mostly octocorals and other unknown fan corals. Close to the summit, scientists observed a large hake and a snipe eel. The current was variable and generally from the northeast to the southwest along the steep slope. The dive ended within 15 meters from the top of the knoll, but the seafloor leading to the peak was covered with corals and sponges. The taxa densities and diversity appeared to increase toward the summit, at the same depths where similar patterns were observed on Carondelet Reef. While it is difficult to generalize these patterns based on only two dives, it will be useful to conduct dives at similar depth ranges on other seamounts to examine if this pattern holds true.