Dive 03: Coral Hotspot
On March 11, scientists explored Carondelet Reef within the Phoenix Islands Protected Area. This was the first deep dive ever conducted in the area. The dive was the most biologically diverse of the dives on the expedition thus far, with scientists documenting at least 32 species of corals, over 21 species of other invertebrates, and five species of fishes. Video courtesy of the NOAA Office of Ocean Exploration and Research, Discovering the Deep: Exploring Remote Pacific MPAs. Download (mp4, 22.6 MB)
This dive was the most biologically diverse of the dives on the expedition thus far, with scientists documenting at least 32 species of corals, over 21 species of other invertebrates, and five species of fishes. The dive track was on the southwest ridge of Carondelet Reef within the Phoenix Islands Protected Area (PIPA). The first deep dive in this area. The dive began around 1,840 meters and finished along a gradual ridge at 1,587 meters. The start of the dive, in the first 20 meters, was very speciose with at least 11 species of corals, including two types of octocorals (some with eggs), stony corals, four black corals with two branched forms and whips, and large bamboo colonies attached to steep rock faces, plus two species of sponges, and several associates. Hemicorallium was the first precious coral observed on the dives thus far. Most of the fan corals were oriented perpendicular to the dominant current, flowing from the northwest to the southeast. As Deep Discoverer moved upslope, new corals seen included species of black coral, rock pens, sea pens, octocorals, soft corals, and bamboo corals. Cup corals were the only scleractinians documented on the dive. Five species of fish were observed: cutthroat eels not observed on previous dives within American Samoa at similar depths, batfish, and a bristlemouth.
At the gently sloped terrain at around 1,700 meters depth, there were more sedimented ledges and sediment-filled rock fissures. The substrate had several long (greater than one meter) bamboo coral whips and a large bamboo colony, estimated to be 300 years old, with several tendrils securing it to the steep rock ledge. Scientist sampled an octocoral and an unknown sponge with associates. The underside of rock ledges were often populated by small colonies of octocorals. Notable non-coral observations included sponges, predation by a sea star on a bamboo whip, crab with an anemone clasped by its posterior limbs, a benthic siphonophore resembling a pipe organ, and a roughly 17 centimeter-long ribbon worm. With nothing previously known about the deep-sea fauna within PIPA, these observations will help with management of biological resources in the protected area. Future dives will clarify if the diversity and abundance of fauna present on Carondelet Reef is representative of the broader region.