Autonomous sub seeks plankton patches to save birds
Phytoplankton aren't just evenly distributed throughout the ocean. Instead, they occur in three-dimensional concentrated patches. A new autonomous underwater vehicle (AUV) is able to find and map those patches, potentially helping to preserve wildlife such as seabirds.
Named after Norwegian oceanographer Harald Sverdrup, the 2 meter-long (6.6-ft) Harald AUV was designed by a team at the Norwegian University of Science and Technology (NTNU).
It's equipped with a device called the ECOpuck. As the watercraft autonomously cruises through a specified section of ocean, that device detects fluorescence produced by what is known as chlorophyll a. That substance is in turn produced by phytoplankton, and it fluoresces red when exposed to light.
Based on how much fluorescence is detected, and in what locations, the Harald's electronic brain can figure out where and how concentrated the patches are. The AUV then travels around them, creating a 3D map as it does so.
A couple of years ago, the vehicle was successfully used to hunt for phytoplankton hotspots near the Norwegian island of Runde. This was actually done in order to determine if a lack of food sources was responsible for a recent drop in local seabird populations. After all, the birds feed on fish, which eat smaller fish, which eat zooplankton (a type of animal), which eat phytoplankton (a type of plant).
Therefore, the fewer the phytoplankton, the less food there would be for the birds. If that same sort of survey were conducted simply by drawing and analyzing water samples off of surface vessels, the scientists wouldn't know if those samples were taken from concentrated patches of plankton, or the open water between them. So far, though, the results of the Runde study are inconclusive.
"We took a snapshot of that area, which tells us something about the current ecosystem at that time," says NTNU PhD candidate Trygve Olav Fossum. "But we'll need to go back and get another snapshot to detect changes and identify potential causes to say something about why the birds are declining."
A paper on the research was recently published in the journal Science Robotics.