From the 26th of April until the 2nd of May MAE PhD student Erik Wurz joined a research cruise with RV Kristine Bonnevie to the Norwegian fjord and shelf area. On board the 56m long and well equipped vessel the ROV Aglantha was stationed and awaiting its descend to the abyssal depths off the Norwegian coast. The researchers on board visited boreal sponge grounds in water depths from 250 to 600m.
Besides doing transects to assess species distributions, biomass etc. the main goal of the ROV operation was the sampling of intact individuals of the massive Demosponge species Geodia barretti. “Massive” not only describes the growth form of this species, but also its size. The biggest issue during the dives was to find small individuals that would fit in the sampling container of the ROV and finally also in the experimental setup in CARUS in Wageningen (average size of encountered Geodia spp. individuals: Basketball size).
Following the dive of the ROV by real-time images, the scientists also encountered the diverse fauna that is associated with deep-sea sponges. For example meter wide colonies of Gorgonians, the cold-water coral Lophelia pertusa, large individuals of Cod and deep-sea sharks. Despite their remoteness and hard accessibility these deep-water ecosystems are under threat from human exploitation. Besides the flourishing and diverse marine wildlife the ROV also bumped into a longline entangled in the steep, rocky relief of the fjord. Due to the actions of the experienced crew, it was possible to remove the fishing gear that was equipped with large hooks. In addition to the ROV also many colonies of cold-water corals and Gorgonians got knotted in the longline.
Perfect weather conditions with a lot of sunshine and little winds made long ROV dives possible. In the end of the cruise, in total 112 sponge individuals (including 52 G. barretti individuals) have been sampled with the especially for this purpose designed manipulator of the ROV. The sampled sponges are now maintained in a flow-through aquaria system at the University of Bergen. Under these conditions Erik is measuring respiration and clearance rates of intact G. barretti individuals. Next week these sponges will join Erik on his flight back to Amsterdam to be transported to the research facilities of Wageningen University and Research for further studies.