February 24, 2020 — Tracking down marine life isn’t easy. Ocean scientists drag nets through the water to find the fish or plankton they are looking for, tag whales with harpoon-like devices, or scuba dive with an erase-proof whiteboard and hand counter to tally reef fish. That’s how you count creatures underwater. But an emerging technology called environmental DNA, or eDNA, is easing this time-consuming and expensive process for scientists by allowing them to grab water samples and check for DNA.
Each drop of seawater contains thousands of microorganisms, as well as bits of skin, mucus, and waste shed by passing fish and mammals. Using a robotic laboratory mounted on an underwater drone that filters and sequences the DNA that it finds, scientists and engineers can now identify marine life without coming back to shore. “You don’t need a big ship to collect your samples,” says Chris Scholin, executive director of the Monterey Bay Aquarium Research Institute, which is developing this new technology along with several other research groups across the US. “This has become portable and small enough to operate in real time on an autonomous underwater vehicle.”
Sampling remotely means that scientists might not have to go to sea in stormy weather to collect data, and can allow them to sample over a long period of time, instead of collecting information during a three- or four-week cruise. It also doesn’t require them to harvest the fish. Robotic vehicles recently traced the DNA of great white sharks congregating in the middle of the Pacific Ocean, tracked tropical fish along the Jersey Shore as they headed north to escape climate change, and found farm-raised fish genes while screening samples from New York Harbor.
This new technology is driven by the marriage of a device the size of a thumb drive called an Oxford Nanopore Minion sequencer to another recent invention, ocean-going autonomous vehicles (AUVs) that no longer take commands from ship or shore. These devices can follow environmental signals, such as temperature, salinity or the optical properties of plankton, just like a hound sniffing out an escaped convict’s trail. (Researchers use sonar to find plankton, the way an angler would use a fish finder.)