Expedition Cruise Report: Cruise EX-15-04 Leg 2--2015 Hohonu Moana: Exploring the Deep Waters off Hawaii (ROV and Mapping) EX-15-04 Leg 2, Hohonu Moana 2015: Exploring the Deep Waters off Hawaii (ROV and Mapping)

EX-15-04-L2 was a combined mapping and ROV cruise to the Papahānaumokuākea Marine National Monument (PMNM) that took place between July 31 and August 24, 2015. During the cruise, 18 ROV dives were conducted from 1,198 to 4,831 m between West Nihoa and Salmon Bank, for a total of over 98 hours of bottom time, and covered a linear survey distance of 6,211 km, including the deepest dive ever conduct inside the PMNM. The first ever sampling by ROV Deep Discoverer was conducted during this cruise, which yielded 31 rock samples and 65 biological specimens, 29 of which were commensal animals collected with the 36 primary specimens. Of those primary specimens, all were collected under the presumption that they might be either new species or new records for the region. The ROV video obtained during EX-15-04-L2 recorded at least 334 different types of organisms, extended the depth range of known communities of high-density coral and sponges at three sites, and discovered new high-density communities at six other sites. EX-15-04-L2 mapping operations mapped over 29,900 km2 of seafloor, including two seamounts inside PMNM and one just outside of the boundary that had not been previously mapped. Important sub-bottom profiler data were also obtained below the seafloor of an enigmatic crater and the summit of an unnamed guyot believed not to be part of the Hawaiian seamount chain. 2020 Ocean Exploration Program Submitted https://doi.org/10.25923/rzp3-6k44 Public Domain 1877