High-frequency study of epibenthic megafaunal community dynamics in Barkley Canyon: A multi-disciplinary approach using the NEPTUNE Canada network

In the deep sea and along the continental slope, benthic observations have often been limited to seasonal or longer time scales, conducted at irregular and intermittent intervals. The recent development of cabled observatories now permits continuous high-frequency studies of the ecology of deep environments, and will bring greater temporal resolution to our understanding of processes that shape benthic communities. Combining high-frequency quantitative biological and environmental data, we studied the epibenthic megafaunal community at 890 m depth in Barkley Canyon off Vancouver Island (BC, Canada) using the NEPTUNE Canada cabled network. A video sweep of the same 5 m2 area was recorded every 2 h during the month of December 1-31, 2011 and examined for species composition and behavior. A suite of instruments provided environmental data at the same location allowing us to relate species and community patterns to environmental variables at different temporal scales using time-series analysis (periodogram and wavelet analyses) and multivariate methods (canonical redundancy analysis and the distance-based Moran Eigenvector Map). At the beginning of our study physical conditions in the lower water column were influenced by a preceding period (late November) of high surface winds and waves that generated enhanced currents down to 840 m depth. These currents created a potentially inhospitable environment for hippolytid shrimp explaining their migration into deeper waters. At the same time a shift in hydrographic properties was occurring in bottom waters with the intrusion of slightly colder (4 to 3.3 °C), and saltier (34.3 to 34.4 psu) waters over approximately 10 days. These changes were accompanied by a shift in benthic community composition from one dominated by hippolytid shrimp to one dominated by buccinid snails. The temporal structure detected in the epibenthic megafaunal community coincided with oscillations detected in the ambient currents. These results reveal the importance of continuous sampling at high-frequency over long durations by enhancing our ability to detect species activity patterns and will contribute to the design of studies and experiments to understand the interaction of factors acting at multiple temporal scales in submarine canyons.