Gelatinous zooplankton abundance and benthic boundary layer currents in the abyssal Northeast Pacific: A 3-yr time series study

Gelatinous zooplankton are prominent fauna in the deep ocean, especially in the water column associated with the sea floor. This interface zone, the benthic boundary layer, is critical to biogeochemical exchanges between pelagic and benthic communities. A conspicuous member of this benthic boundary layer community in the abyssal Northeast Pacific (Sta. M; 4000 m depth) is the hydrozoan medusa, Benthocodon pedunculata. A 3-year time-series study was conducted of B. pedunculata from October 2014 to November 2017 using an autonomous time-lapse camera system and acoustic current meter deployed on the sea floor. Remotely operated vehicle benthic video transects and collections were also conducted during six servicing cruises for the long-term instruments. Over three years, a total of 123,887 B. pedunculata were recorded in hourly images with densities ranging from 0 to a high of 33 individuals m−3 in March 2016. Density of B. pedunculata was highest when current speeds were low, and declined precipitously as speed increased beyond ~1 cm s−1. Movement of B. pedunculata was parallel to the continental margin in northwest and southeast directions. The large numbers of B. pedunculata observed over this 3-year study suggests their ecological importance in the benthic boundary layer food web at Sta. M.