Underwater robot can follow marine organisms over record distances

Nature News: Underwater robot can follow marine organisms over record distances
Versatile vehicle can spend months studying ocean ecology.

Sandeep Ravindran


The Tethys can travel much further than other underwater robots.Todd Walsh / MBARIAn underwater robot that can function in the ocean for months on end will allow scientists to study life in the open ocean, hundreds of kilometres from shore. The robot performed its first experiments this month, spending almost a week at a time tracking algal blooms in California's Monterey Bay.

"We really think this is a revolution in vehicles," says the robot's creator Jim Bellingham, chief technologist at the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing. "It changes how we do oceanography."

Oceanographers currently use a variety of underwater vehicles in their research, none of which is ideal for studying marine life. Non-propelled vehicles called 'gliders' can stay in the ocean for several months and are great for studying its physical properties, but they are too slow and their sensors too limited for detailed studies of living organisms. Current underwater robots, meanwhile, are fast and have sophisticated sensors, but these drain their batteries within a day, leaving researchers with only brief snapshots of life in the ocean.

“I'm a big fan of Tethys. It has a combination of speed and endurance and range that other vehicles don't have.”
Eric D'Asaro
University of Washington
The new robot, called the Tethys, combines the speed of existing robots with the range of gliders. It's designed to pursue organisms while recording the physical and chemical properties of the water around them.

"The idea is to be able to develop 'life stories' of marine organisms by following them as they move through the ocean," says Bellingham. The Tethys will be only a little more expensive than gliders, which cost about $140,000 — cheap enough for individual labs to buy, he adds.

Bloom boon
The robot's first scientific expedition included studies of a bloom of the toxic algae Pseudo-nitzschia australis, says John Ryan, an oceanographer at MBARI.

The robot has the unique ability to 'park' itself in an algal patch and drift along with it]. Once the Tethys had pinpointed the centre of each patch, scientists sent in another short-range robot for more extensive analysis, and the two robots performed what Ryan calls a "robot ballet".


The robot finished its first experiments last week, tracking algal blooms in California's Monterey Bay.Todd Walsh / MBARIFrancisco Chavez, a senior scientist at MBARI, says he's excited by the thought of using the robot for other projects. One of his ideas is to study how whirlpool-like eddies hundreds of kilometres from shore affect the ocean environment. Because of the time taken to travel to them by ship, by the time a typical 20–30-day expedition reaches an eddy they have just five days or so to study it before they need to return to shore. The Tethys "will allow us to follow these eddies for essentially an unlimited time," Chavez says.

Eric D'Asaro, a professor of oceanography at the University of Washington in Seattle, says that he could use the Tethys to track algal blooms in the North Atlantic. He currently uses a combination of gliders, floating sensors and ships. The Tethys would be better at sampling the complexity and diversity of life in the ocean over long distances and timescales, D'Asaro says.

"I'm a big fan of Tethys," he says. "It has a combination of speed and endurance and range that other vehicles don't have."

Magic moment
MBARI scientists designed and built the Tethys over the past three and a half years. Bellingham says that they wanted to overcome some of the unique difficulties of tracking life in the ocean. A terrestrial biologist studying a forest can keep going back to it, but in the ocean, the current moves everything around, and if scientists try to go back to the same place after a two-day hiatus, he says, "instead of a forest, they're now looking at the Sahara Desert".

The Tethys will help oceanographers to conduct more experiments from shore, reducing expensive and time-consuming ship voyages, because scientists can modify the robot's missions and receive data from it via satellite. "To be at home at 2 a.m. and seeing the data coming in was pretty magical," Bellingham says.

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MBARI researchers are working on a way for the Tethys to bring back water samples, and plan to outfit it with a small DNA analyser that can identify microorganisms. They could add more sensors later, including ones that track ocean carbon and acidification to monitor the effects of climate change.

The scientists are currently building a second version of the Tethys, and hope eventually to deploy a team of robots to simultaneously track different organisms in the food web, from algae to marine mammals. The Tethys will undergo longer tests next spring in preparation for major offshore experiments in July and August. Bellingham says he hopes to license the vehicle for commercial manufacture within six months. He is currently setting up collaborations with other researchers, and has already received funding from the National Science Foundation for a joint project to study mixing of ocean waters.

And if researchers really want to stretch the robot's abilities, "we should be able to drive it from Monterey to Hawaii on a single charge", says Bellingham.