A deepwater longtail red snapper (Etelis coruscans) measuring one meter (three feet) long, observed at 353 meters depth on a southeastern ridge off Ta’u island, within National Marine Sanctuary of American Samoa.

A deepwater longtail red snapper (Etelis coruscans) measuring one meter (three feet) long, observed at 353 meters depth on a southeastern ridge off Ta'u island, within National Marine Sanctuary of American Samoa. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2017 American Samoa. Download larger version (jpg, 1.7 MB).

Dive 02: Ta'u Unit of National Marine Sanctuary of American Samoa
February 17, 2017
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Dive 2: Armored Searobin

Video of a searobin using modified fins to move across the seafloor during a dive within the Ta'u Unit of National Marine Sanctuary of American Samoa. It’s a fish out for a stroll!

Armored sea robins are related to the sea robins found in shallow water along the Atlantic and Gulf of Mexico coasts of the U.S. They differ from shallow water sea robins by having four rows of bony plates along the body. Each plate has a thick, curved, short spine—hence the common name. They also have horn-like projections on each side of the snout and branched barbels (whiskers) on the bottom of head in front of the mouth. The branched barbels have taste buds and are used to sense food on the bottom.

The fan-like fins on each side of the body behind the head (pectoral fins) have stiffened rays. In sea robins, including the armored sea robin, the first few rays are free from the membranes of the rest of the fin and are very thick. The fish uses these thickened, stiff fin rays to "walk" along the bottom. That is the usual form of locomotion for sea robins, instead of swimming like most other fishes. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2017 American Samoa. Download (mp4, 17.7 MB)

The dive began at a depth of around 500 meters on the ridge extending away from the southwest side of Ta'u, a relatively flat area consisting of basalt rock lightly dusted with a light-colored sediment, and ended within the bounds of the Ta'u Unit of National Marine Sanctuary of American Samoa. Several striped squat lobsters, large-clawed hermit crabs with zoanthid symbionts, cup corals, robin fish, large-eyed shrimp, red/purple urchins, chrysogorgiid coral, a snake eel, and a toad fish were all observed in this area. Moving northward along the top of the ridge were larger basalt boulders, many sponges, ophiuroid brittle stars (including a species with stripped arms and red oral disk with white dots), different fish species, sea stars, corals, and crinoids. As Deep Discoverer (D2) continued along the dive track, the bottom composition appeared to vary; at different points it appeared to be carbonate, then clay, and later volcanic sediment welded together possibly with a chemical precipitate "cement." At the top of the ridge, a peculiar folded-fan shape primnoid octocoral was collected; it had associated snapping shrimp and a tiny yellow squat lobster. A pencil urchin, potentially feeding on spider crab, as well as a fourth kind of crinoid were also seen in this area. Numerous crevices in the rocks had ophiuroids living in them. Great abundance of red/purple echinothuriid urchins were seen as well – it was an echinoderm wonderland! Cardinal fishes hid in the cracks and D2 observed noticeably fewer suspension feeders than at shallower depths. Around 350 meters, animal abundance increased, with plentiful soft corals, yellow crinoids, and several half- living stony corals. During collection of a mushroom octocoral, we observed shimmering water from thermocline fluctuations (plus or minus 1°C). Commercially important bottomfish, including snapper and several seabass, were first observed in shallower water. When we got to the top of a flat terrace, we observed a new kind of stalked crinoid as well as many "fried egg" anemones. There was an incredible abundance of dead skeletons, potentially black corals, overgrown by what seemed to be hydrozoans. At the end of the dive, we sampled a basaltic rock as we observed numerous anemones and mushroom corals.