Beautiful Bubbles Make Massive and Biodiverse Seamounts
by Heidi Gartner and Cherisse Du Preez
Cherisse (left) and Heidi (right) working on a sample together.
We are researchers that go on expeditions hundreds of kilometres offshore of British Columbia to study the deep sea. We use remotely operated vehicles (ROVs – robots with cameras, lights, sensors, and sampling equipment) that remain tethered to the vessel and transmit data and imagery by cable technology to the team studying from above. The dives descend from the sunlit surface and enter a world of darkness, where we turn on the ROV lights to illuminate an incredible world in the depths of our ocean. Not just barren plains as once thought, our deep sea has an incredible density of Ecologically and Biologically Significant Areas (EBSAs), where life thrives in the deep. These include seamounts that rise over a kilometre above the ocean floor, hydrothermal vents from which super-heated and mineral-rich water spews from the ocean floor, tall stands of coral and sponge gardens, and cold seeps where gas bubbles out of the seafloor.
Wrap-up video from the 2023 Northeast Pacific Deep-Sea Expedition.
ROV at surface from the authors’ 2023 expedition. Photo: Nicole Holman, Fisheries and Oceans Canada/Pêches et Océans Canada
“Our team has turned our research attention to cold seeps of late, hence the yelling of ‘Bubbles!’ multiple times a day. ”
An ROV measures the volume of gases emanating from the seafloor at a cold seep site. Extensive carbonate rock provides habitat for many animals including the mushroom corals and rockfish pictured here. Photo: NEPDEP expedition partners, CSSF ROPOS
Life at sea on a deep-sea expedition is both thrilling and exhausting. The consequences of spending weeks onboard a vessel, seeing only the open ocean and about thirty other people, working long shifts, and troubleshooting in a dynamic environment may reveal themselves in strange ways. Like the obsessive joy of shouting “Buuuubbles!” at a TV screen, like some hyper - active Yellow Tang Fish in Nemo, while watching dives into the deep sea. You also start to question yourself when you witness incredible discoveries… like instead of the idiom “making mountains out of molehills” you watch your screen and consider “are mountains being made from bubbles?” Okay, let us explain. Our team has turned our research attention to cold seeps of late, hence the yelling of ‘Bubbles!’ multiple times a day. Cold seeps are areas where fluids enriched with reduced chemicals (e.g. methane and hydrogen sulphide) emanate from the seafloor. Amazingly, life can thrive here. Microbes, or bacteria, use these chemicals to fix carbon, forming the base of rich food webs and creating biological hotspots [1]. Here in the deep sea, instead of using sunlight (photosynthesis) to create life, chemicals (chemosynthesis) are the foundational building blocks for life. As you can imagine, many of these animals are only found in these distinct environments, so in addition to improving local productivity, they also boost regional diversity [2].
In 2018, Canadian Pacific cold seeps were evaluated as being EBSAs, which comes with some conservation considerations. The designation was made because cold seeps host unique and rare species, have special importance life history stages of species, and are vulnerable, fragile, and slow to recover from disturbance (e.g. bottom-contact fishing) [3]. Since 2018, the Deep-Sea Ecology Program at Fisheries and Oceans Canada has been focusing on better understanding these ecosystems in the Pacific to provide scientific advice for their conservation and management (i.e., potentially helping create Marine Protected Areas). This research is a collaboration with Natural Resources Canada and GEOMAR (in Germany), with explorations organized as part of the NorthEast Pacific Deep Exploration Project (NEPDEP)—a United Nations Ocean Decade endorsed collaboration between the Deep-Sea Ecology Program, coastal First Nations, Ocean Networks Canada, Royal BC Museum, and academia.
Deep-sea Octopus nursery grounds (left to right): two females are observed on a large carbonate boulder; a zoomed in focus on the eggcases between a mother’s arms; and a female fending off a Short-spined King crab. Photo: NEPSEP expedition partners, CSSF ROPOS
Our current data suggest that there are close to 1,600 cold seep sites in Canadian waters. Seeps are mapped using echosounders (similar to bats using echolocation) where the sound waves are used to both detect bubble plumes in the water column but also the structure and shape of the seafloor. Cold seeps can have complex physical structures associated with them as reactions between the methane, bacteria activity, and seawater form carbonate rock [4]. Yes, the bubbles make rocks! While these geological processes that create complex topography have been studied at cold seeps, our recent visual surveys, combined with echosounder data, show the structures they can form are more vast than we previously thought. And these bubbles emanating from the seafloor have created mountain-like features in our ocean basin!
“It was mesmerizing to see and consider that all these incredible mountain-like deep sea features formed from bubbles coming from the seafloor. ”
For example, off the west coast of Haida Gwaii, what was once thought to have been a single seamount (formed from volcanic activity) is now determined to be a chain of mud volcanoes (a completely different origin story and structure, where mud and rock get bubbled to the surface with the gases) that create a ridge along the continental shelf that is over two kilometres high and over sixty kilometres long [5]. In the Winona Basin, off the west coast of Vancouver Island, the bubbling has created a twenty-five kilometre long ridge, 500 metres high, covered (or entirely created) by carbonate rock [6]. At this site, in addition to the chemosynthetic community, we observed an abundance of commercially and culturally important fish and crab species. We also observed that on the Hesquiaht Slope there is a large mound 750 meters across and sixty metres high that has carbonate boulders and hydrate chunks (methane forms ice structures!) [7].In maneuvering the ROV around these “underwater icebergs” and large carbonate boulders, we started noticing Deep-sea Octopuses curled upside down in the pockmarked features of the carbonate rock. We quickly realized that this hard carbonate rock provides rare hard substrate in the deep for the octopuses to lay and care for their eggs (which, as the world-record holder of longest incubation period, they do for over four years!). We documented a nursery ground for Deep-Sea Octopuses and even witnessed a mother fending off Shortspined King Crab. As anyone who’s watched “My Octopus Teacher” will know, grab a tissue before watching this video of an octopus’s care for her young:
Launching underwater cameras from the John P. Tully research ship, scientists are able to collect images and data thousands of metres below. Photo: Fisheries and Oceans Canada
It was mesmerizing to see and consider that all these incredible mountain-like deep sea features formed from bubbles coming from the seafloor. These beautiful bubbles not only create complex features and chemosynthetic communities, but also have cascading ecosystem effects to the larger deep-sea community. Unfortunately, we also had the opportunity to witness the anthropogenic effects humans have on even these remote environments. We documented lost fishing gear and even the devastating effects of bottom trawl impacts on these environments (they were broken up, flattened, with little signs of life). And as our new findings show, we lose a lot when we lose cold seeps. In summary, cold seeps can shape the ocean floor. They are important fish habitat and nursery grounds supporting biodiversity. Additionally, the communities and geological processes at cold seep sites provide a major biological filter preventing large amounts of these gases from reaching the ocean surfaces and storing carbon naturally in the deep[8].By protecting these habitats from destructive activities, we may better serve to protect life in the ocean and life as we know it. Months after returning to land, regaining our “land legs” and clearer minds, we are still amazed by the incredible large effects these beautiful little bubbles have on our planet.
References
1. DFO (Fisheries and Oceans Canada). 2018. Science Response 2018/002. Assessment of Canadian Pacific Cold Seeps against Criteria for Determining Ecologically and Biologically Significant Areas. 35p.
2. Le Bris, N., Arnaud-Haond, S., Beaulieu, S., Cordes, E.E., Hilário, A., Rogers, A.D., van de Gaever, S., and Watanabe, H. 2016. Chapter 45. Hydrothermal vents and cold seeps. First global integrated marine assessment. United Nations. p. 1-18. (Accessed 28 November 2017).
3. DFO (2018).
4. Summarized in DFO (2018).
5. Du Preez, C., et al. in prep. An updated understanding of cold seeps in Pacific Canada. Can. Tech. Rep. Fish. Aquat. Sci.
6. Du Preez, C., et al. in prep; Unpublished data but dive available on SeaTube under Expeditions>Department of Fisheries and Oceans Canada>2023>DFO Expedition 2023-05 (May 2023)>R2311 and R2312
7. Du Preez, C., et al. in prep; Unpublished data but dive available on SeaTube under Expeditions>Department of Fisheries and Oceans Canada>2023>DFO Expedition 2023-05 (May 2023)>R2316
8. Sommer, S., Pfannkuche, O., Linke, P., Luff, R., Greinert, J., Drews, M., Gubsch, S., Pierper, M., Poser, M., and Viergutz, T. 2006. Efficiency of the benthic filter: Biological control of the emission of dissolved methane from sediments containing shallow gas hydrates at Hydrate Ridge. Global Biogeochem. Cycles 20: GB2019. doi:10.1029/2004GB002389.