Dive 13: Mona Island Escarpment

Date: November 13, 2018
Location: Lat: 18.20885°, Lon: -67.80160°
Dive Depth Range: 409-566 meters (1,340-1,855 feet)

One of the most noteworthy sightings of Dive 13 was an urchin that was in the process of feeding on a black coral. Black corals are predominantly found in deep water and little is known about their basic ecology, including what feeds on them. 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, 1.5 MB).
The orange roughy (Gephyroberyx sp.) was the most common fish observed on Dive 13. 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).
This demosponge (Phakellia sp.) was one of the largest sponges seen on Dive 13. Demosponges were the most common group of sponges seen on today’s dive. Most of these were, however, rather small in size. 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, 1.1 MB).
This urchin (Histocidaris nuttingi) uses its long spines for defense and for moving along the seafloor. The small hooks on the spines are used for manipulating food. 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, 1.3 MB).

During today’s dive, we explored seafloor habitats northeast of Mona Island at depths between 409-566 meters (~1,340-1,855 feet). The substrate consisted mostly of broken off veneers along a steep slope. These veneers created relief and small crevices, which served as habitat for a myriad of different invertebrates. Sponges were particularly abundant and covered a large portion of the seafloor. Most of the sponges were small in size, but they became larger at shallower depths. Demosponges contributed the most to the overall sponge composition, and there were also a lot of encrusting sponges, including blue and yellow varieties.

While not as abundant nor diverse, we also saw several different groups of corals on today’s dive, including black corals, scleractinian corals, stylasterids, and various octocorals. We also observed numerous sea urchins on the seafloor. Particularly noteworthy was the sighting of one sea urchin eating a black coral. Crinoids, both stalked and unstalked, were also quite abundant throughout the dive.

In contrast to the high biodiversity of invertebrates, fish diversity was rather low at the site. We saw a total of seven different species of fish, including queen snapper (Etelis oculatus), toad fish (Chaunax sp.), snake eel (Aoterichtus distocopera), shortnose greeneye (Chlorophthalmus agassizi), scorpion fish, wrasses (Polylepion sp.), and orange roughy (Gephyroberyx sp.), the latter of which was the most abundant fish at the site.

A beautiful basket star (Gorgonocephalus sp.) perched on a sponge. Basket stars are echinoderms and belong to the same group as the brittle stars. The names “Gorgos” and “-cephalus” refer to Gorgon’s head from the Greek myth, who has coiled serpents for hair. As seen in the video, the basket star is composed of a set of very intricate arms, and when open, they are shaped like a basket. Many times you see them closed and coiled up on branching organisms like octocorals. However, this basket star has its arms open—a real treat! This could mean that it is suspension feeding on small crustaceans and other plankton in the water. The arms of basket stars are covered with spines and hooks which allow them to collect small critters.

Text contributed by Stacey M. Williams, Institute for Socio-Ecological Research, Coastal Survey Solutions LLC.

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, 60.2 MB).

Location of Dive 13 on November 13, 2018. Download larger version (jpg, 2.2 MB).

The remotely operated vehicle track for Dive 13, shown as a white line. Scale is water depth in meters. Download larger version (jpg, 334 KB).