Dataset: Bulk isotopic composition (d15N and d13C) of abyssal megafauna and macrofauna from Stations M and Aloha

Macrofauna and megafauna were collected in May and October 2019 using the HOV Alvin and the ROV Doc Ricketts, respectively, at Station M (34° 50'N, 123° 00'W) and in July 2019, January 2020, and July 2020 using ROV Lu'ukai at Station Aloha (22° 45'N, 158° 00'W). Macrofauna at Station M were collected using HOV-operated Ekman cores (20x20 cm). Macrofauna at Station Aloha were collected using a Brenke epibenthic sled towed across the seafloor (detailed in Glover et al 2016), due to the considerably lower macrofaunal densities at this oligotrophic site. Megafauna were collected using the submersible vehicle's manipulator arm and/or slurp gun. Upon retrieval to the surface, samples were placed in a cool room (5ºC) for their further processing. Specimens of megafauna were weighed and measured, then they were dissected using a scalpel. All tissue samples were placed in cryovials and frozen in liquid nitrogen, and subsequently stored at -80ºC. Sieved (300 um) macrofauna samples were preserved in 10% buffered formalin. In the laboratory, macrofauna were further sorted by taxon. Samples of megafauna body tissues or macrofauna were freeze dried and ground to a homogenous powder using mortar and pestle.

For analysis of bulk nitrogen and carbon isotopic composition, ~0.7 and 3 mg of body tissue from holothurians and echinoids, respectively, ~ 5 mg of gut content, and ~ 20 mg of sediments were placed in silver capsules. Samples were acidified to remove carbonates with 1M HCl, which was added dropwise until bubbling ceased, then dried at 60ºC and packed.