Wednesday, August 10, and
Thursday, August 11:
We completed the CTD series and performed several additional lowerings in order to try to pinpoint dissolved methane sources around gas crater features. Some preliminary analysis of bottom photos taken on this cruise suggest that microbial mats, possibly fed by methane release, may represent a substantial source of productivity in bottom habitats that are clearly productive of monkfish and deep sea red crabs, and witch flounder, as well as non-resource species like longfin hake, all of which we saw in abundance.
Large anemones (Bolocera tuediae and Actinauge sp.) are the most conspicuous structural species on most substrates, often at densities of several individuals per square meter. While these are neither deepwater corals nor sponges, they likely represent long-lived and readily damaged habitat structural species paralleling the role of corals and sponges elsewhere. We speculate that benthic decapod shrimp, which we also saw in considerable abundance, particularly where filamentous microbial fouling was evident, could form a link between microbial chemosynthetic production and deepwater fisheries production.
We had a lot of difficulty with the onboard computer system in the MolaMola AUV. It kept rebooting itself unpredictably, which triggered an emergency surfacing routine. Once at the surface, the computer could be reset, but a lot of time was lost because both ascent and descent of neutrally buoyant MolaMola require powered vertical thrust. However, we managed one more successful dive on a hard bottom “buttress” feature along the eastern wall of Hudson Canyon, where we anticipated finding deepwater corals. These results are not yet available at the writing of this message.
Mapping of tilefish bottom with ME70 proceeded in order to better define the local distribution of habitat of this resource species and its relationship to the topography and hydrology of the canyon. Two large areas were mapped, one west and one east of the canyon.
The last dive of MolaMola photographed a few red crabs, but only through a blinding “blizzard” of marine snow: nearly white-out conditions in which we could barely see the bottom, even a close range. Marine snow is a common phenomenon in near-bottom waters caused by a dense concentration of white particulate matter, mainly organic in nature, suspended in the water. That we saw such an intense case of the phenomenon in this dive was itself of interest, as the marine snow material is a potential feast for bottom animals and microbes: a potentially important link in the canyon food chain.
HB11-04 Habitat Mapping Cruise
Henry B. Bigelow returned to port on Friday morning, August 12, completing the Hudson Canyon habitat mapping cruise.