Dive 19: Mona Seamount

Date: November 19, 2018
Location: Lat: 19.2781°, Lon: -67.68402°
Dive Depth Range: 4,927-5,000 meters (~16,165-16,405 feet)

Polynoid worm seen on soft sediments at the beginning of Dive 19. 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).
Geological bedforms were observed over steep rocky slopes explored during Dive 19. These formations were often cracked and full of loose debris. 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, 1.2 MB).
The black coral Abyssopathes cf. lyra was one of only two species of corals observed on this dive. The black coral genus Abyssopathes is among the deepest-dwelling corals known to occur. 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).
Dandelion siphonophore seen near the end of Dive 19. 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).

The 19th and final dive of the 2018 Océano Profundo expedition explored the north slope of Mona Seamount near the Puerto Rico Trench. Targeting a maximum depth of 5,000 meters (16,405 feet), this was by far the deepest dive of the expedition, as well as one of the deepest dives ever to reach the seafloor in this part of the world. Soft sediments dominated the first part of the dive, with occasional patches of cobbles and boulder-sized rocks. Umbellula sp. sea pens and polychaete worms were seen on the soft sediments.

Later in the dive, we came upon rocky outcrops that displayed linear features that resembled bedding planes. Some rocky outcrops were composed of cracked angular rocks. These rocky areas provided habitat for a few cladorhizid sponges and tube-dwelling anemones. Other organisms were surprisingly diverse at this site given the extreme depth and included munnopsid isopods, polynoid worms, Munidopsis sp. squat lobsters, a stalked crinoid, echiurans, a dandelion siphonophore, a black coral (Abyssopathes cf. lyra), xenophyphores, as well as three individuals of the cusk eel Leucicorus atlanticus.

The deepest dive of the expedition to a depth of 5,000 meters (16,405 feet) on Mona Seamount was also one of the deepest dives ever to reach the seafloor in this part of the world. Despite the depth of the dive, the site was not devoid of life, as we saw sponges, corals, anemones, and even some fishes. 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, 72.7 MB).

Location of Dive 19 on November 19, 2018. Download larger version (jpg, 2.2 MB).

The remotely operated vehicle track for Dive 19, shown as a white line. Scale is water depth in meters. Download larger version (jpg, 385 KB).