Dive 03: “Okeanos Ridge”
December 2, 2017
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Dive 03: The Sea Spider Stroke

This sea spider, or pycnogonid, was seen swimming through the water during Dive 03. Video courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico 2017. Download larger version (mp4, 20.0 MB).

Today we explored an area that we have called “Okeanos Ridge,” as it was first mapped by NOAA Ship Okeanos Explorer in 2012. The dive took place within a proposed Habitat Area of Particular Concern, so we were interested in collecting baseline information on the local distribution and abundance of life on the seafloor. We arrived on a sediment-covered canyon floor at a depth of 740 meters (2,428 feet). During the dive, the remotely operated vehicle Deep Discoverer (D2) climbed two areas of an escarpment and crossed the exposed platform between the areas, leading to a variety of benthic habitats. Communities appeared to increase in abundance and diversity as D2 progressed up the escarpment, with the largest coral colonies and greatest abundances of organisms close to the exposed crest; small areas of sediment on the escarpment supported less fauna. As D2 crested the escarpment and followed the exposed edge eastward, we observed a variety of striking carbonate structures, including caves, pillars, and even an “amphitheater,” created when numerous slabs calved off a low wall. Corals observed during the dive included at least five species of black corals; the octocorals Chrysogorgia sp., Acanthogorgia sp., Pseudoanthomastus sp., Plumarella sp., and Isididae sp.; and the stony corals Madrepora oculata, Lophelia pertusa, and Enallopsammia sp. Other organisms included zoanthids, hydroids, featherstars, hexactinellid sponges and purple demosponges. We also observed two mating pairs of golden crabs (Chaceon fenneri), a Gracilechinus urchin and a Circeaster sea star preying on octocorals, and a wood fall (possibly bamboo), which served as habitat for animals such as gastropods and shrimp. Notable water-column observations included two swordfish, a swimming pycnogonid (sea spider), and two cutlass fish (Benthodesmus tenius).