Dive 05: Colorful Chimaeras
Ghost shark, ratfish, spookfish, or rabbitfish – doesn't matter what you call them, chimaeras are always a favorite fish to see during dives. During Dive 05 of the expedition, we encountered these two particularly colorful chimaeras while exploring "Stetson Mesa South" at ~700 meters (2,296 feet) depth. Most closely related to sharks, chimaeras are cartilaginous and have no real bones. They are known to only live in deep water.
Video courtesy of the NOAA Office of Ocean Exploration and Research, Windows to the Deep 2018. Download larger version (mp4, 32.8 MB).
The dive today was proposed by partners at NOAA Deep Sea Coral Research and Technology Program and NOAA National Centers for Coastal Ocean Science to have potentially suitable habitat for deep-sea corals in a poorly explored area, the Stetson Mesa. As discussed during yesterday’s daily update, dives on these unexplored areas can provide much needed data to further inform the habitat suitability models and allow for better predictions of the locations of these sensitive and ecologically important species.
The dives today and tomorrow will investigate knoll/mounding features that are fairly characteristic of this region of the Blake Plateau. This region is part of the Stetson Miami Terrace Habitat Area of Particular Concern and was mapped by NOAA Ship Okeanos Explorer in 2012 and 2014, revealing an extensive area in the southwestern portion of the Blake Plateau that is covered with mounds. Scientists predicted these mounds would be biogenic in origin (created by an animal, like a coral), fitting in with other known mounds nearby, but they weren’t sure until the remotely operated vehicle (ROV) reached the seafloor today. So these dives will help resolve a mystery for this region.
The ROV Deep Discoverer was on the seafloor from 13:29:37 - 20:05:13 UTC. The dive started at 719 meters (2,359 feet) and traversed three large mounds at approximately 730 - 700 meters, with the dive ending around 708 meters (2,323 feet). A rock collection during the dive verified that the rubble was coral rubble cemented together by iron-oxides and compacted sediments. This provides further evidence that the mound shapes were created by the biology (“biogenic”) over many generations of coral skeletons building on each other and trapping sediments to form the mounds. The compacted dead coral rubble found exposed as a layer low on the mound’s slope indicates that this area has been suitable coral habitat for many thousands of years.
Crests of all three mounds were home to more abundant, higher diversity of corals and sponges. These communities were concentrated on standing dead coral skeletal framework, rather than on the surrounding rubble that had a low density of fauna. The highest/shallowest mound, where the greatest current velocities occurred, had the largest skeletal framework structures. Low areas between the three mounds explored in this dive were clearly more sedimented, with only sparse populations of deep coral, indicating lower current velocities. The scleractinian corals, Enallopsammia profunda (deeper mounds) and Lophelia pertusa (mound crests), were the dominant structure-forming corals, with the dead coral matrix creating habitat for many other species. Some of the other species seen throughout the dive included octocorals, alcyonacean corals, black corals, an octopus, urchins, brittle stars, cutthroat eels, reef codlings, several golden crabs, a shark, and a few rays. Stay tuned for the dive summary for a comprehensive list of the species observed during the dive.
With today’s mystery solved and tomorrow’s still unexplored, stay tuned in for the dive tomorrow at Stetson Mason North to complete this game of clue.