Close up of a basket star, with commensal ophiuroids. We saw an extremely high density of these on this dive, and believe this may have been a new species.

Close up of a basket star, with commensal ophiuroids. We saw an extremely high density of these on this dive, and believe this may have been a new species. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas. Download larger version (jpg, 1.1 MB).

Dive 12: Zealandia
May 3, 2016
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Basket Star City

An aggregation of basket stars like this is a rare sighting. These gorgonocephalid basket stars are close relatives of brittle stars and feed by perching in an elevated position and extending their arms in a net-like fashion perpendicular to the current to catch small crustaceans, jellyfish, and other small animals that come within reach. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas. Download (mp4, 83.0 MB)

Dive 12 was on Zealandia Bank to explore for deep-sea coral communities and survey shallower depths for bottomfish fishery habitat. When we first got to the bottom at 650 meters, we saw many rounded cobbles that were cemented within a carbonate matrix, which we interpreted as having possibly been formed on a high-energy beach. Later in the dive we entered an area of flat, thick rocks that we interpreted as either igneous flows or a carbonate platform, and then a very low-relief crust in the later part of the dive. We collected an unidentified black coral early on in the dive. As we continued on, we started to see occasional basket stars, which are elaborately branched relatives of the brittle stars. The density of these continued to increase until we encountered a field of basket stars, something none of us had ever seen before. The basket stars were large, but we succeeded at collecting one. We transited through an area with fewer fauna and then into a field of Parisis corals. We collected an astrophorid demosponge, also known as a lithistid or "rock sponge" because it has interlocking silica spicules that form a rigid skeleton. Some lithistids contain chemicals with therapeutic pharmaceutical properties, and we believe this occurrence may be a new record. Throughout the div,e we also saw precious corals, sponges covered in benthic ctenophores, crinoids, crabs, urchins, and cookie stars. We saw a high diversity of fishes on this dive, including boarfish (Antigonia), deepwater squirrelfish (Plectranthias), two sand tiger sharks (Carcharias taurus), a lestidiid fish (“deep-sea naked barracudina”) --  the only fish known to have bioluminescent tissue in its liver, a Lophiodes (anglerfish relative), and the commercially valuable deepwater red snapper (Etelis coruscans). The very last organism that we saw before heading back to the surface at 286 meters was another fisheries target, the Oblique banded snapper (Pristipomoides zonatus).