When water flows through pores in carbonate rock, dissolution can happen, causing these dramatic overhangs. Three different primnoid coral species are on top of this rock, which became the dominant fauna upslope. Image courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico 2018. Download larger version (jpg, 1.0 MB).
Bright yellow parasitic zoanthids were observed encrusting a glass sponge. Image courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico 2018. Download larger version (jpg, 776 KB).
This spiny rockfish (Trachyscorpia cristulata) has large eyes, a large head, and a tapering body. It was observed at ~435 meters (~1,425 feet) deep. Image courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico 2018. Download larger version (jpg, 935 KB).
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.