The hadal lander returns from a deployment to 5,000 meters last week. Photo by Ken Kostel, Woods Hole Oceanographic Institution.
Despite some technical setbacks, the HADES team has so far successfully deployed Nereus to 4,000 meters and the fish trap, hadal lander, and abyssal lander eight times to depths ranging from 4,000 meters to 5,100 meters. The expedition is currently in Auckland awaiting repairs to the crane that deploys and recovers Nereus.
Initial observations from the lander images by Alan Jamieson and Thomas Linley from the University of Aberdeen have shown the expected transition in fish community composition from one dominated by rattails at 4,000 meters to the beginnings of the deeper, cusk eel-dominated communities further down. The hadal lander also captured video footage of cusk eels feeding on amphipods near the bait, the first recorded observations of their feeding behavior.
Individual fish brought to the surface in the trap deployed by Jeff Drazen, Clif Nunnally, and Mackenzie Gerringer of the University of Hawaii are being recorded, dissected, and sampled for identification and analysis of age and growth rate, feeding behavior, and environmental adaptations. Amphipods are also being brought to the surface for analysis of their adaptations to increasing pressure, as well as their reproductive stages and strategies. Several individuals of fish and amphipods have been identified as possible new species, but confirmation of this will require more careful taxonomic analysis than possible on board the Thomas G. Thompson.
Data from a respiration experiment deployed with Nereus to 4,000 meters and transferred to the hadal elevator has begun to reveal differences in the metabolic rates of some common benthic organisms found at abyssal (4,000 to 6,000 meters) and hadal (more than 6,000 meters) depths. Oxygen consumption by brittle star, two sea cucumbers and two anemonesover 24 hours has shown that, without accounting for non-water body mass, the brittle star has the more active metabolism, likely because it is the more mobile of the group, but that the anemones may slightly outpace the sea cucumbers. Further respirometry data from more individuals combined with data for species abundance and particulate carbon will help refine estimates of carbon uptake and sequestration in ocean trenches.Even these preliminary results speak to the general lack of even basic knowledge about the deep ocean and hadal ecosystem. That's why the scientists, engineers, and crew of the Thomas G. Thompson are anxious and eager to return to the waters over the Kermadec Trench. Once repairs to the crane are complete and a new Nereus tether is on board, the NSF-funded expedition will do exactly that, and continue their work exploring along the trench and nearby slope to the abyssal plain.