With the advent of cabled observatories scientists are now able to have a permanent presence in the deep-seafloor, being able to reveal previously unseen faunal behavior as well as to track long-term changes in biodiversity and ecosystem function. The Ocean Networks Canada 800-km loop regional seafloor observatory array located in the NE Pacific has instruments measuring a variety of environmental variables ranging from temperature, salinity, oxygen, currents, turbidity, fluorescence, etc, at multiple and very high temporal resolution scales. High-definition video cameras also monitor benthic communities in multiple deep-sea habitats, all at some extent influenced by an oxygen minimum zone (OMZ). In the present study, whale-bone and wood substrates are being used to evaluate bathymetric, regional and inter-basin variations in benthic biodiversity and connectivity, as well as interactions between biodiversity and ecosystem function. In May of 2014 three humpback whale (Megaptera novaeangliae) rib sections, one 20x20x10 cm block of Douglas Fir (Pseudotsunga meniziesii), and a ~ 30x30x30 block of authigenic carbonate were placed with the use of an ROV at 890 m depth inside Barkley Canyon. The substrate packages were placed concentrically, 45-cm away from a HD video camera. Five-minute videos were captured at 2-hr intervals. Moving averages (12 and 48 hr) were calculated for abundance and species richness, and waveform analysis at a 24-hr time scale was used to assess the relationship between animal activity (abundance counts) and tidal regimes. We used pressure data from a CTD as a proxy for tidal dynamics. Bacterial mat coverage at the surface of the whale bones was measured by means of manual image analysis using a masking tool on image J software. Environmental variables measured from ONC’s Barkley Canyon POD3 CTDs (temperature, pressure, dissolved oxygen, fluorescence, turbidity) were used to explore environmental variability. Data analysis from 8 months of deployment showed very distinct early community succession patterns between the two organic substrates (bones and wood) and the authigenic carbonate. Whalebones and wood showed amphipod (Orchomene obtusa) abundance peaks mostly contained during the first 60 days after deployment; Amphipod peak abundance rapid decline coincides with rapid growth of bacterial mat on whalebone and wood surfaces. Specifically for the whale bones, community composition seems to be responding to sulfide build up from bacterial mat degradational processes, and switching from a mobile-scavenger directly into a sulfophilic stage (sensu Smith and Baco 2003). Absence of Osedax and Xylophaga on whale bones and wood, respectively, concur with our hypothesis of OMZ effects in reducing colonization rates by specialized macrofaunal decomposers. Low abundance, species richness and substrate degradation rates are in agreement with a low oxygen environment of the OMZ in the canyon. Even though data analysis is still underway, this experiment demonstrates how cabled observatories are suited for conducting experiments in the deep-sea, where researchers gain full control of observation parameters and benefit from high-frequency measuring of environmental fluctuation.
Smith, CR., Baco, AR, 2003. Ecology of whale falls at the deep-sea flloor. Oceanography and Marine Biology, An Annual Review, 41, 311–354