A cluster of sea urchins (and a single crinoid), living on an elevated rocky feature. It is typical for suspension feeders, such as the crinoid, to live on elevated features such as this to get access to food from the currents in the water column, however it is not clear why these urchins were so densely clustered here. Until this dive, we have not encountered such a high density of urchins in any one location. It may have been a spawning aggregation.

A cluster of sea urchins (and a single crinoid), living on an elevated rocky feature. It is typical for suspension feeders, such as the crinoid, to live on elevated features such as this to get access to food from the currents in the water column; however, it is not clear why these urchins were so densely clustered here. Until this dive, we have not encountered such a high density of urchins in any one location. It may have been a spawning aggregation. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas. Download larger version (jpg, 904 KB).

Dive 18: Esmeralda Bank
May 9, 2016
Access Dive Summary and ROV Data

Dive 18 took place on the outer slope of the Esmeralda Seamount, a submarine volcanic complex to the west of Saipan. The location we dove on, an extinct part of the volcano, is of interest to NOAA Fisheries because there is significant bottom fishing occurring in this area. We began our dive at 520 meters and transited up the slope of the bank. Between 450-500 meters, we saw some of the highest density communities of corals and sponges of the expedition. There were also high numbers of urchins in this area. We saw a significant shift in the geology during the course of the dive, from volcanics at the beginning to karstic carbonate rocks that may have been old coral reefs toward the end. We saw a number of animals on this dive that we hadn't yet seen on the expedition, including a very abundant tubular sponge (Psilocalyx wilsoni), a slit shell gastropod (Pleurotomariidae; part of an ancient lineage referred to as a "living fossil"), onaga (Etelis coruscans) – the most important fishery species in the region, and a nudibranch. The jelly-nose eel (Guentherus katoi) and the guyot butterflyfish (Prognathodes guyotensis) may both be new records for the area. We also encountered many deepwater cardinalfish (Epigonis); roughies (Hoplostethus); boarfishes (Antigonia); a bright orange batfish (Halieutaea stellate); an Ornate Jobfish (Pristipomoides argyrogrammicus); many of the small, colorful Odontanthias; and a tonguefish. We collected a demosponge that had a high number of commensals living on it, and a chrysogorgid coral with lots of comb jellies (ctenophores) attached to the polyps and zoanthids lining the stalk. Just before leaving the bottom, small schools of pelagic dogtooth tuna (Gymnosarda unicolor) and jacks swam by.