A rare encounter with a swimming dandelion siphonophore on Dive 17 at Farallon de Medinilla. This dandelion is actually comprised of many individuals that all work together with some protecting the colony, some catching food, some reproducing, etc. These animals are usually observed anchored to seafloor. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas. Download (mp4, 59.7 MB)
On Dive 17, we explored the slope of Farallon de Medinilla, a small, uninhabited island north of Saipan, to search for precious coral and bottomfish fishery species of interest to managers. This dive began at a depth of 500 meters and moved upslope to end at 250 meters. In the depth range of 400-500 meters, the seafloor was characterized by areas of fragments of calcified red and green algae, urchin spines and tests, and other unidentified hard organic material, as well as carbonate rock cobbles. These features suggest the area had once been a reef, perhaps of Pleistocene age. Around 350 meters, we started seeing larger rocks that looked more in place (possibly cemented to the seafloor), with hydrozoans and stylasterid and plexaurid corals. We collected a plexaurid coral. As we moved into depths of 250-300 meters, the character of the seafloor changed, with areas of limestone (possibly karstic with dissolution pits) and cemented carbonate crusts, with some shell hash between them. We collected a carbonate rock towards the end of the dive. We did not encounter any precious corals, but did see many fish, including an armoured sea robin (Scalicus engyceros), a moray eel (Gymnothorax berndti), a duckbill fish (Chrionema chryseres), a dragonet (Callionymidae), and the first squid of this expedition. We spent a lot of time transiting along the 250-meter contour, where we encountered a number of the commercially targeted bottomfish, such as the snappers Pristipomoides zonatus (oblique-banded), P. argyrogrammicus, P. auricilla, and the golden grouper (Saloptia powelli). This was one of the shallowest dives ever conducted by the remotely operated vehicle Deep Discoverer and a number of colorful shallow-water fish were also seen: squirrelfish (Holocentridae), the snapper Randallichthys filamentosus, Odontanthias sp., and a batfish (Ogcocephalidae).