Dive 11: South of Long Mounds and Midwater Transects
April 28, 2018
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Dive 11: Age and Beauty

Much like shallow-water coral reefs, reefs in the deep sea, like those that are built by the stony coral Lophelia pertusa, host rich and diverse communities. These rich ecosystems contain many species that are slow-growing and long-lived. Individual corals of L. pertusa have been dated to be 1,000 years old, and some Lophelia reefs are estimated to be 40,000 years old. Understanding where these ecosystems are found has important implications for management and conservation. Video courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico 2018. Download larger version (mp4, 37.1 MB).

Today’s dive surveyed a previously unexplored site located between Long Mounds and Many Mounds, two areas that the Gulf of Mexico Fishery Management Council is currently considering for the establishment of new habitat areas of particular concern (HAPC). Remotely operated vehicle Deep Discoverer (D2) landed at ~530 meters (1,740 feet) deep on a heavily sedimented, flat surface at the base of a large mound where there was little current. Heading upslope, carbonate rock rubble became more abundant and increased in size from cobbles to small boulders. Abundant fish, echinoderms, and arthropods were observed, as well as a dense community of Lophelia pertusa corals that was attached to the tan, weathered rock. In some places, dead coral skeletons obscured the underlying rock surface. D2 explored a second, adjoining mound with dense coral communities attached to the rock, similar to the first mound. While transiting east to a third mound, D2 went over a sedimented bottom with periodic small rock mounds and scattered rock rubble. Pronounced, asymmetrical, linear ripples in the sediment indicated a prevailing north-south current. Deep scour marks on the lee side of some rocks indicated high current velocity. Man-made debris (bottle, metal barrel) was observed during this transit. The third and largest mound was composed of weathered, carbonate rock with dense coral and sponge communities, similar to the other mounds.

The most commonly observed animals on the seafloor portion of the dive were dead and alive Lophelia pertusa corals, including a single individual, noteworthy due to its orange coloration. Other animals included various species of octocorals and black corals, sponges, squat lobsters, zoanthids, golden crabs, urchins, crinoids, seastars, anemones, and octopi. Fish recorded included blackbelly rosefish, roughy, cusk eels, toadfish, thorny tinselfish, rattails, hatchetfish, catshark, codling, rockfish, scorpionfish, hake, herring smelt, cardinalfish, duckbill flathead, slope dragonets, batfish, blackmouth bass, armored searobin, and a swordfish.

The seafloor portion of the dive ended at a final depth of 478 meters (~1,568 feet). D2 ascended to 460 meters (~1,510 feet) to begin a series of midwater transects. Other targeted depths for midwater transects were 400 meters (~1,310 feet) and 300 meters (~985 feet). Animals observed while exploring the water column included ctenophores, polychaetes, siphonophores, salps, larvaceans, hatchefish, and two cephalopods.