Visual monitoring of key deep-sea megafauna with an Internet Operated crawler as a tool for ecological status assessment

Abstract The spatio-temporal distribution of seven abundant morphospecies (i.e. taxa identified based on morphological traits) and the diversity of the benthic megafaunal community at the Barkley Canyon hydrates site (870 m, Vancouver Island, BC, Canada) were assessed in 18 linear imaging transects (each transect ~30 m long), conducted with an Internet Operated Deep-sea Crawler in November 2016. Faunal counts (as proxy for local abundances) were treated as Poisson-behaving variables and were modeled and correlated to habitat quality (i.e. level of physical seafloor disturbance, as previously induced by the crawler), fluctuating oceanographic conditions (i.e. tides and currents, seasonal transitions and episodic particle fluxes) and temporally and spatially varying food availability (i.e. elevated chlorophyll levels, proximity to the hydrate mounds as additional energy sources). The model outcome was used to establish a potential trigger-notification procedure for substrate disturbance monitoring when ratios of faunal abundances exceed the expected range for any morphospecies. Finally, a quality assessment of the crawler’s performance as a multidisciplinary monitoring platform was performed using individual and morphospecies accumulation curves, which aids in optimizing and standardizing data collection protocols. We showed that the abundances and diversity of hydrates megafaunal community differed in relation to physical seafloor disturbance, proximity to the hydrate mounds and episodic food input, at varying degrees. Our work sets a solid base for the future real-time, long-term monitoring of ecosystem functioning and health status in deep-sea areas exposed to industrial substrate alterations (i.e. mining, fisheries, etc.).