In certain areas of the Nova Scotian shelf, Vazella pourtalesii (Hexactinelid) forms dense monospecific aggregations. Vazella creates complex 3-dimensional structures, which provide habitat to a wide range of associated species, enhancing local diversity. In 2013, the Canadian authorities established the Sambro Bank Sponge Conservation Area, banning bottom fishing activities. However, this protection zone has not yet been incorporated into a management plan requiring implementation of monitoring strategies that account for natural variability. To elucidate assemble dynamics and response to environmental variability, a NIOZ-designed lander equipped with a HD-video camera, ADCP, CT and oxygen sensors was deployed at 154m depth for 10-months. A total of 5,151 still images were obtained of which 1157 were manually analyzed with the BIIGLE 2 software, and posteriorly used to train a mask convolutional neural network. Over 30,000 organisms belonging to 8 different species were identified. An unidentified actinian and the red fish Sebastes fasciatus were the most abundant species accounting for 93% and 4% of all observed organisms, respectively. Non-metric multidimensional scaling analysis revealed that assemblage composition did not significantly differ between seasons. However, it was observed that sessile taxa abundances decreased during benthic storms that influence the near-bed hydrodynamics. These storms could last for several days causing high sediment resuspension and the dislodgment or partial burial of sponge and actinian individuals. We also observed that sponge individuals attached to small cobbles, moved across the field of view. Moving individuals intermittently appeared laying horizontally on the seafloor or standing in an upward position, within short intervals. Bottom currents may cause Vazella individuals, attached to small cobbles, to tip and rise progressively, dislodging them from their original position depending on current intensity and direction. Our results highlight the importance of time-series studies as megafaunal community structure is reactive and dynamic

This study is part of the SponGES project, which received funding from the European Union’s Horizon 2020 Research and Innovation Program under grant agreement no. 679849. Cruises were funded by Fisheries and Ocean’s Canada’s International Governance Strategy. Jordi Grinyó has received funding form the European Union’s Horizon 2020 research and Innovation programme. Action MSCA-ST fellowship, CWCC-Dynamics Grant agreement no. 101028621

11th World Sponge Congress, 10-14 October 2022, Leiden

Peer reviewed