Dive 05: “Incised Escarpment Ridge”
December 4, 2017
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Dive 05: Life on a Glass Sponge

Seen during Dive 05 of the expedition, this elegant glass sponge provides a home for gooseneck barnacles, brittle stars, and anemones. Video courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico 2017. Download larger version (mp4, 30.1 MB).

Today’s dive was the first of a pair of dives along the northern end of the West Florida Escarpment that compared the geology and associated communities at the two sites. The southern section of the escarpment explored today is marked by promontory features, which have steep slopes that are both sedimented and exposed, resulting in a high species diversity. The dive started at ~2,210 meters (7,250 feet), on a sedimented slope, where Umbellula sp. octocoral, our first for this expedition, was spotted immediately. On this slope, we also observed at least three species of sea cucumbers, shrimp, a xenophyophore, a few fish, and spoon worm feeding tracks. Areas of exposed carbonate rock upslope were colonized by several sponge species, including a number of dead glass sponges with extensive communities of soft coral, barnacles, brittle stars, and amphipods growing on the stalks. We also observed a high diversity of cnidarians on this slope, including at least 12 species of coral. The dive ended in a sedimented area with rock outcrops that hosted sponges, polychaete worms, crinoids, soft corals, octocorals, and bamboo corals.

After leaving the seafloor, we conducted midwater exploratory transects at four depths (900, 700, 500, and 300 meters; 2,953, 2,297, 1,640, and 984 feet). During the midwater survey, we observed a diverse assemblage of organisms, including larvaceans, shrimp, siphonophores, salps, fishes, and several different species of hydromedusae and ctenophores. The greatest diversity and biomass of organisms were observed at 500 meters.