Dive 07: Mud Volcano in WR 488
April 20, 2018
Access Dive Summary and ROV Data

Dive 07: Flight of the Sea Cucumbers

During the Gulf of Mexico 2018 expedition, we have encountered many deep-sea holothuroids (sea cucumbers) that not only swim, but rise, sink, and hover. These behaviors suggest that some species are specially adapted to manage their buoyancy (the force that allows something to float, sink, or remain neutral in a liquid) remarkably well. How do they do it? Read the full video caption to find out. Video courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico 2018. Download larger version (mp4, 23.3 MB).

Overnight mapping indicated that this previously unexplored mud volcano might contain some exposed hard substrate. Remotely operated vehicle Deep Discoverer (D2) reached the bottom on a heavily sedimented surface at a depth of 2240 meters (~7,350 feet). Several Lepidisis caryophylla bamboo corals were seen close to the landing spot, as was a plastic bag with anemones growing on it. D2 ascended a side of the mud volcano and proceeded east. Continuous fine-grained sediment covered the western side of the mound, interspersed with occasional patches (less than 15 square meters) of stained sediment and bacterial mats, suggesting discharge of subsurface fluids. A very small area (less than one square meter) of exposed asphalt flow with attached anemones was observed. Moving towards the center of the mud volcano, the seafloor bathymetry became more undulated. Occasional small mounds were observed, including one surveyed on the side of a depression that appeared to be recently formed.

The heavily sedimented slopes of the mud volcano had sparse colonies of bamboo coral (Lepidisis caryophylla). Other invertebrates recorded in the sediment included sea cucumbers (Benthodytes sp. and Chiropdota heheva), shrimp (Nematocarcinus ensifer, Mysidae, Hepomatus tener, and Cerataspis sp.), Venus fly-trap anemones (both Homethiidae and Actinoschyphidae), as well as a single sea pen (Anthopthilum sp.), and a tube-dwelling anemone (Ceriantharia). Fish observed included spiny eel (Polyacathonotus merretti), rattail (Coryphaenoides rudis), cutthroat eel (Synapobranchus sp.), halosaur (Aldrovandia sp.), tripod fish (Ipnops murrayi), cusk eel (Cataetyx laticeps), and nettastomatid eel (Venefica procera).

Throughout the central portion of the mud volcano, small patches with bacterial mats and chemosynthetic communities were observed, which included high densities of siboglinid tubeworms (Sclerolinum sp.), amphipods, shrimp (Escarpia sp.), and sea cucumbers (Chirodota heheva). In one on these patches was a low mound with white sediments on one side, suggesting fluidized mud flow from a hole on the top of the mound. Closer inspection revealed fecal casts in that hole, leading to uncertainty as to whether the small mound feature was geological or biological in origin. The northern rim of the mud volcano revealed a similar benthic environment to that previously observed. D2 moved to the outer edge of the mud volcano in search of hard substrate, but found none. With the exception of the asphalt flow, no rock or hard substrates were recorded on this dive.

Dr. Heather Olin’s Boston College Deep-Sea Biology class participated from shore at the Inner Space Center and asked the science team great questions, which prompted interesting discussions among the scientists. Additionally, the dive featured a live interaction with the Exploratorium. At the end of the dive, the ship was directed to transit to Pascagoula for necessary repairs to the port motor.