High-frequency observations from a deep-sea cabled observatory reveal seasonal overwintering of Neocalanus spp. in Barkley Canyon, NE Pacific: Insights into particulate organic carbon flux

• Published in: Progress in Oceanography
• Main Authors: De Leo, Fabio Cabrera, Ogata, Bruno, Sastri, Akash R., Heesemann, Martin, Mihály, Steven, Galbraith, Moira, Morley, Michael G.
• Other Authors: Universidade Estadual Paulista (UNESP)
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: Barkley Canyon; Carbon flux; Life history; NE Pacific; Neocalanus plumchrus; NEPTUNE cabled observatory; Overwintering; Zooplankton; Canada; Pacific; Subarctic; Copepods
• Online Access: http://hdl.handle.net/11449/171314; https://doi.org/10.1016/j.pocean.2018.06.001

Canada Foundation for Innovation Ministry of Education Many submarine canyons are known hotspots of pelagic and benthic biodiversity and productivity. Despite a very limited knowledge of the ecology, biodiversity and ecosystem function of Canada's West Coast canyons, Barkley Canyon is becoming a relatively well studied system, particularly after the installation of the NEPTUNE seafloor cabled observatory in 2009. Video observations of large densities of overwintering calanoid copepods (likely a combination of Neocalanus plumchrus, N. cristatus, and a small contribution of N. flemingeri) drifting near the bottom at 970 m in the axis of Barkley Canyon motivated our interest in investigating the temporal dynamics of their ontogenetic migration cycle. Particularly, since these large calanoid copepods, and especially Neocalanus plumchrus, comprise up to 50% of of the mesozooplankton biomass in the subarctic NE Pacific, being considered a keystone species in the trophodynamics of pelagic ecosystems in the region. Here we used ∼20-months (May 2013–Jan 2015) of seafloor video imagery combined with acoustic Doppler current and backscatter time-series data from the NEPTUNE observatory to identify the precise timing and seasonal and inter-annual variability in the deep ontogenetic migration of Neocalanus spp. in Barkley Canyon. A total of 33,486 still images were extracted from 1674 × 5-min segment videos, captured at two-hour intervals, and used in a computer-automated image analysis protocol designed to estimate Neocalanus spp. densities near the seafloor. The results from the entire time-series revealed close correspondence with the described developmental and reproductive cycle for Neocalanus spp., with the highest densities of copepodite-5 (C5) and adult individuals present at depth from the late fall and through the winter. The concomitant high-frequency (2 MHz) ADCP backscatter time-series nearly mirrored the patterns obtained from the video imagery, and also highlighted a clear inter-annual variability, with ...