Dive 02: Deep-water Margarita Snail
This snail, in the family Margaritidae, was observed moving quickly across the seafloor during the dive at a site unofficially dubbed "Te Tukunga o Fakahotu," just north of the Manihiki Plateau. The snail is using its foot to tumble along, likely as an escape mechanism. Video courtesy of the NOAA Office of Ocean Exploration and Research, Mountains in the Deep: Exploring the Central Pacific Basin. Download (mp4, 20.9 MB)
During Dive 02, we explored a rocky, mesa-shaped feature at a site unofficially dubbed "Te Tukunga o Fakahotu," just north of the Manihiki Plateau. This was the first-ever remotely operated vehicle exploration in the area. Beginning at a depth of ~2,480 meters, this dive was nearly seven times as deep as Dive 01. At the start of the dive, the seafloor was composed of black manganese-encrusted rock, which appeared to be volcanic in origin. We collected a rock from this area to be analyzed for composition and age. Light-colored biogenic sediments (likely foram shells) had collected in the areas between these rocks. As we moved along the dive track, we saw an increase in rock rubble. Near the base of a small cliff, we collected another rock sample for further study. Although the density of fauna was fairly low throughout the dive, we saw a large variety of different kinds of animals living at these depths. The most abundant were stalked tunicates, xenophyophores, and brisingid sea stars. Corals included a rock pen, three species of bamboo corals, and a black coral. One bamboo coral had a spiny-armed brittle star (Ophiacanthidae) positioned on a part of the colony lacking tissue; this observation has now been made a number times and begs the question of whether the brittle star causes the loss of tissue or whether it takes advantage of a bare spot on the colony. Representatives of all five echinoderm classes were observed during the dive. At least four species of crinoids (sea lilies and feather stars), four species of sea cucumbers, two species of sea stars (including a slime star), a sea urchin, and one species of brittle star seen on a bamboo coral. Interesting observations included a tumbling Margarita snail and a stalked crinoid with multiple predatory snails feeding on its stalk. When we brought rock samples collected during the dive into the wet lab, we were able to recover some very small organisms from them, including a branching foraminifera; and bryozoans. We also recovered a verrucomorph barnacle, which is asymmetrically developed; this is thought to be a feeding adaptation to the food-poor deep sea that enables these barnacles to catch crawling benthic prey rather than just swimming prey. Surprisingly, not a single fish was seen on the dive, despite the fact that fish often occur in regions of soft sediments because there are often more prey there.