The VENUS cabled observatory as a method to observe fish behaviour and species assemblages in a hypoxic fjord, Saanich Inlet (British Columbia, Canada).

Studies reporting processes that may shape marine benthic communities under the seasonal scale are rare at depths >50 m. In this study, the use of the VENUS multidisciplinary cabled observatory provided 2-month high-resolution data combining quantitative biology and environmental data in Saanich Inlet, a seasonally hypoxic fjord located on Vancouver Island (British Columbia, Canada). An ecological module equipped with a camera acquired a 3 min video clip every half hour during 2 months at 97 m depth in the oxygen fluctuation zone of the fjord. Results highlighted the role of the tidal cycle on species activity rhythms and confirmed the influence of oxygen fluctuations on benthic assemblage structure and species behaviour. However, environmental variables considered only explained a small proportion of the total variance in species data. This study demonstrates how seafloor observatories can be used to study species behaviour and community dynamics in relation to abiotic conditions by providing continuous access to multidisciplinary data. [ABSTRACT FROM AUTHOR]