Giant larvacean could help the battle against climate change
A strange sea creature that lives 1,000 feet below the surface encased in a giant bubble of mucus may be key to removing carbon dioxide from the atmosphere. The giant larvacean captures carbon-rich particles in its balloon-like mucus webs that stretch up to three feet across. These bubble-houses are discarded and replaced regularly as the animal grows in size and its filters become clogged with particles. Once discarded, they sink to the seafloor and encapsulate the carbon for good, preventing it from re-entering the atmosphere. Larvaceans also capture and dispose of microplastics in this way, which can come from clothing and cosmetics and often ingested by other marine species. Researchers used a system of lasers mounted on a 12,000 pound robot to map the giant larvaceans delicate body in a series of 3D images. Mucus is ubiquitous in the ocean, and complex mucus structures are made by animals for feeding, health, and protection, said lead author Kakani Katija, principal engineer at the Monterey Bay Aquarium Research Institute (MBARI) in California. Now that we have a way to visualise these structures deep below the surface we can finally understand how they function and what roles they play in the ocean. Larvaceans are abundant throughout the worlds ocean basins and range from less than half an inch to nearly four inches in length. The giant larvacean, or Bathochordaeus, lives at depths of up to nearly 1,000 feet, in the 'ocean twilight zone', just beyond the reach of sunlight. Giant larvaceans create balloon-like mucus webs that can be more than three feet across, which surrounded small, fist-sized inner filters that the animals use to feed on tiny particles and organisms. Quntities of carbon float though the water as what is known is marine snow a shower of organic waste that sinks towards the ocean floor. This process of carbon-rich fragments sinking deeper into the ocean is key to the worlds global carbon cycle the cycle of carbon between the atmosphere, the oceans, land, and fossil fuels. But giant larvaceans can help control this process with their exterior bubble-like mucus filter. As they swim through the waters, they beat their tail to pump water and collect and eat food particles using its inner filter. However, its outer filter traps plant debris and food particles too big for the animal to eat and other pieces of debris not for consumption. When their filters become clogged, the animals release the mucus, which rapidly sinks to the seafloor. This helps the ocean remove carbon dioxide from the atmosphere and also carries microplastics from the water column down to the seafloor. Larvaceans can filter a wide variety of particles while processing very large volumes of water up to 80 litres an hour. Previous studies have looked at smaller larvacean filters in the laboratory, but the delicacy of the giant creatures mucus bubble means other methods are needed to closely study them. The team therefore developed an instrument called DeepPIV deep particle imaging velocimetry to scan giant larvaceans in their native waters. Mounted on a remotely operated vehicle (ROV), DeepPIV projects a sheet of laser light that illuminates particles in the water, like dust in a sunbeam. By recording the movement of these particles, researchers can document tiny currents around marine animals and the water flowing though their filters. As the ROV moved back and forth, the sheet of laser light revealed a series of cross sections through the transparent, gelatinous bodies and mucus filters. By assembling a series of these cross sectional images, the team were able to create 3D reconstructions of individual larvaceans and their filters, much like how radiologists image the insides of human bodies from CAT scans. Using DeepPIV to collect these 3D cross sections is probably the hardest thing I've ever done with an ROV," said Knute Brekke, chief pilot for the ROV. We were using a 12,000 pound robot to move a millimetre-thick laser sheet back and forth through a larvacean and its fist-sized mucus filter that was drifting hundreds of meters below the ocean surface. Combining 3D models of larvacean filters with observations of flow patterns through the filters, the team could identify the shape and function of different parts of the larvacean's inner filter for the first time. Using 3D rendering software, they were able to virtually fly through the inner filter and study the flow of fluid and particles through different parts of the filter. Now we have a technique for understanding the form of these complex structures, and how they function no one has done in situ 3D reconstructions of mucus forms like this before, Katija said. Among other things, we're hoping to understand how larvaceans build and inflate these structures. Expanding on this work, the MBARI is experimenting with new 3D imaging systems that capture precise information about the intensity, colour and direction of light in a scene. They are also working on new underwater robots that will be able to follow gelatinous animals through the water for hours or days at a time. In this paper, we have demonstrated a new system that operates well with a variety of underwater vehicles and midwater organisms,' said Katija. Now that we have a tool to study the mucus filtering systems found throughout the ocean, we can finally bring to light some of nature's most complex structures. The study has been published in .