Minion-Like 'Larva Bots' Roam the Seas, Uncovering Secrets
Grant Susner leans over the edge of a boat in Bodega Bay, stretches his arm toward the waves and releases "Bipinnaria" into the wild.
Bipinnaria -- bright yellow against the deep blue surface -- begins floating away from the boat, bobbing from side to side in the choppy water. Susner is principle marine electronics technician at the UC Davis Bodega Marine Laboratory and his natural habitat is the marine lab's main research vessel, the Mussel Point.
Soon Bipinnaria is joined by its comrades: Hippolyte, Velella, Veliger and Zoea. They drift away swaying in synchrony, like soldiers who've decided to waddle instead of march.
These small robots are serving the cause of marine ecology. Their names give clue to their mission -- that is, if you majored in marine biology. Each moniker is the name of the free-swimming larval stage of a marine animal. After hatching from eggs, certain sea stars spend their early days as bipinnaria. Some shrimp have a Hippolyte phase (named for an Amazonian queen). Velella are jellyfish. Veliger, clams and sea snails. Zoea are crab.
The job of these robots is to behave as much as possible like marine larvae themselves, albeit ones that can transmit their location, send email and take cues from curious researchers.
Splashing Conventional Wisdom
Steven Morgan, a marine ecologist at UC Davis, uses these robots to learn about how marine larvae move, where they are likely to go, how they return to the shore, and how larvae might fare in the face of intensifying ocean acidification and rising temperatures.
"You see a tiny larvae, and it's out [in the ocean] developing for weeks and months -- how is it able to make its way back on shore?" asks Morgan. "People around the world have been trying to answer this question for decades."
Whether you're into fishing for salmon or spotting sea anemones while exploring tidepools, the fate of marine larvae matters to you. (They also happen to be beautiful, like microscopic architectural gems.)
Understanding how larvae disperse is important for managing fisheries, designing and running marine reserves, and controlling invasive species. But modeling their dispersal has been difficult before now. Prior to the development of these "ABLE" drifters, (Autonomous Behaving Lagrangian Explorers), it was essentially impossible to predict where larvae would travel. But evidence has been mounting that larvae aren't just aimless drifters; they control their movements.
One of the early surprising results has been how close to shore most marine larvae linger. Rather than dispersing into the open ocean, most species stay within a mile of shore. They move up and down in the water column to return to shore on currents they use like an underwater subway.
Morgan believes larvae are pre-programmed to return to shore, using environmental cues and subsurface currents.
"There are a lot of skeptics out there that microscopic larvae have any control over where they're going in this wild and woolly ocean of ours," he says. Experiments with his larva bot flotilla will, he hopes, provide the needed evidence to change minds.
Results like this could reinforce the importance of keeping coastal waters free of pollution.
"California has made a big investment in a network of marine protected areas," says Tom Maloney. As executive director of the Ocean Science Trust, Maloney has a keen interest in Morgan's work. His organization, a non-profit created by the state of California to provide science-based management advice, is trying to understand how changes in the climate will change conditions in the oceans.
"We want to understand the full life cycle for this important suite of invertebrates [and fish]," he says. "It'll help us understand if our protected areas are achieving the results we want."
Come Get Me
When it is time for Bipinnaria to return to the boat, it surfaces, communicates its coordinates via a satellite relay and sends Susner an email. The message: Here I am. Come get me.
After a little scouting, boat maneuvering and some skillful scooping with a fish net, all five bots are safely back in the boat.
The lab currently has a small navy of 25 "larva bots." Soon they'll double that.
The strength of the larva bots -- although they are far larger than the creatures they mimic -- is that they move with the currents, as larvae do, and they can be programmed to mimic certain behaviors. They can move up or down in the water column at the same speed as larvae, maintain buoyancy, and respond to light, temperature, salinity or pressure in the same way larvae might.
The bots are built to be "simple and cheap." Even so, fully loaded with LEDs, trackers, GPS and satellite communicators, and sensors to log salinity, temperature, light, depth and swimming speed, the price tag for each is about $1,200. The housings are made from expired fire extinguisher canisters, donated by fire departments. The 'petals' forming a skirt around their waste, which spin to record vertical velocity, were cut by hand. For scientific equipment, they're surprisingly cute. Susner and Morgan show off their capabilities in the lab with obvious affection.
"These things are wonderfully built," Susner says.
After some trial and error in the design data, collection began in earnest last year. (Several years ago, before the retrieval mechanisms were perfected, three bots were lost to the waves). With the arrival of 25 more bots in the coming weeks, data collection is about to go into overdrive.