Large aggregations of crinoids were seen on top of the ridge during Dive 18. Image courtesy of the NOAA Office of Ocean Exploration and Research, Exploring Deep-sea Habitats off Puerto Rico and the U.S. Virgin Islands.Download larger version (jpg, 932 KB).
Stylmetra spinifera crinoid seen swimming through the water column on Dive 18. Image courtesy of the NOAA Office of Ocean Exploration and Research, Exploring Deep-sea Habitats off Puerto Rico and the U.S. Virgin Islands.Download larger version (jpg, 804 KB).
Histocidaris sp. sea urchin preying on a Crinometra sp. crinoid by pinning it down. Image courtesy of the NOAA Office of Ocean Exploration and Research, Exploring Deep-sea Habitats off Puerto Rico and the U.S. Virgin Islands.Download larger version (jpg, 1.6 MB).
Diverse invertebrate assemblage of crinoids, corals, and sponges seen near a topographic high point of Dive 18. Image courtesy of the NOAA Office of Ocean Exploration and Research, Exploring Deep-sea Habitats off Puerto Rico and the U.S. Virgin Islands.Download larger version (jpg, 948 KB).
Dive 18 explored a small ridge feature located west of Desecheo Island at depths between 307-367 meters (~1,005-1,205 feet). The organisms in highest abundance on this ridge were crinoids, sponges, and branching octocorals. Crinoids were particularly abundant on this dive, and we discovered an impressive field of Crinometra sp. crinoids along the edges and on top of the ridge. We also frequently saw two other species of crinoids on top of the ridge (Endoxocrinus sp. and Holopus rangii), as well as individuals of Stylmetra spinifera swimming in the water column. Sponge cover was also very high near the edge of the ridge, and small brown bryozoans were extremely abundant on the ridge crest.
Deep-sea corals were also abundant, as well as more diverse than at other sites in this depth range explored during this expedition. Antipatharians and primnoid octocorals were the most species-rich taxa with four represented species for each group. Chrysogorgia sp. colonies were common throughout the entire dive with many small colonies seen on both sloped and flat hard bottom. The most dense deepwater coral communities occurred at a topographic high point of the ridge (~350 meters; 1,148 feet) where we encountered an abundance of mixed-species assemblages including two species of plexaurids corals (Paramuricea sp. and Scleracis sp.), Acanthogorgia aspera, Nicella sp., stylasterids, and cup corals.
Fish diversity was low with only seven species identified during the dive. The most abundant fish were queen snapper (Etelis oculata). Other fish spotted on this dive included toadfish (Chaunax sp.), wrasse (Polylepion sp.), boarfish (Antigonia capros), yellowfin flagfin (Aulopus filametosus) and bigeye soldierfish (Ositchtys trachypoma). The dive also provided views of small sea stars and cidarid urchins, and we saw a Histocidaris sp. sea urchin eating a Crinometra sp. crinoid. The urchin had pinned the crinoid down and was eating one of its arms, a new behavior observed in this species of urchin. Fishing gear (line and weights) was widespread at this site.
Deepwater feather stars, or crinoids, are rarely found in such abundance on the seafloor as seen in this video. On this dive, we came across a dense field of feather stars, some being grazed upon by cidaroid urchins, one of their dominant predators. If necessary, some crinoids are capable of swimming short distances to escape predators or find better locations to feed. They do this by undulating their arms in a mesmerizing manner, gaining some distance above the seafloor, and gliding downward to a soft landing. Video courtesy of the NOAA Office of Ocean Exploration and Research, Exploring Deep-sea Habitats off Puerto Rico and the U.S. Virgin Islands.Download larger version (mp4, 57.6 MB).
