Dive 12: South of Okeanos Ridge
April 29, 2018
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Dive 12: Fishy Fumble

The squat lobster Eumunida picta got its name “picta,” meaning “painted” from its bright colors. This squat lobster usually lives among hard coral colonies, but this fellow has wandered away into a crack. It looks like he’s fishing, but squat lobsters are just too slow to catch anything as agile as a fish. They usually eat small marine worms or crustaceans or scavenge on dead animals. Probably what is going on is that the squat lobster is trying to get the fish to go away.

Notice those long, waving, whip-like antennae. Squat lobsters and other related crustacean families use those antennae somewhat like cat whiskers, to locate objects and especially to maintain individual distance – the space between one squat lobster and another.

Other squat lobster species that live among larger corals or feather stars may steal some of the protective slime from a coral and eat it, but they will try to warn off intruders on “their” coral by spreading those pincers. (We don’t know if this squat lobster does that).

Text contributed by Mary Wicksten, Texas A&M University Video courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico 2018. Download larger version (mp4, 35.1 MB).

Dive 12 targeted an area located just south of Okeanos Ridge, a priority area identified by the Gulf of Mexico Fishery Management Council for the potential establishment of a habitat area of particular concern (HAPC) in the future. After reaching the seafloor on a heavily sedimented surface with exposed barren rocks at ~510 meters (~1,675 feet) deep, remotely operated vehicle Deep Discoverer (D2) moved upslope on the west side of a large ridge. Large carbonate boulders were intermixed with black nodular rocks that appeared to have a weathered, iron oxide crust. Corals, sponges, and fishes became more abundant as D2 moved shallower. At the flat top of the ridge, thick plates of black iron oxide crusted the tops of carbonate boulders and were inhabited by abundant coral, sponge, and fish – primnoid corals were the dominant fauna observed. As D2 moved north along the ridge, the iron oxide ridge cap was continuously undercut by dissolution and erosion of the underlying carbonate rock, as evidenced by numerous voids and caverns in the carbonate rock face. Some ledges extended out over a meter from the rock face. Corals and sponges were attached to the underside of the overhang, but in much lower abundances than on top of the ridge. Collapsed sections were observed in multiple locations. Leaving the western edge of the ridge and heading east, the iron oxide crust had little to no sediment cover. The abundance of coral and sponges remained relatively constant but the represented species changed—most notably from primnoid to bamboo coral dominance.

The most commonly observed animals were the primnoid coral Candidella imbricata, demosponges, and glass sponges. Other species observed included various species of octocorals and black corals, sponges, squat lobsters, zoanthids, crabs, urchins, crinoids, sea stars, anemones, and bryozoans. Fish included alfonsino, roughy, cardinalfish, cusk eels, toadfish, blackbelly rosefish, rattails, codling, rockfish, scorpionfish, seaperch, stout beardfish, and a cutthroat eel.