Underwater Gliders Join Ocean Survey, Revealing Diverse Marine Life Driving Marine Ecosystem

Research ships from the marine research alliance California Cooperative Oceanic Fisheries Investigations , or CalCOFI, have surveyed ocean conditions off the West Coast for more than 75 years.

Last spring, the ship surveying waters off Southern California had company.

Two autonomous underwater gliders, operated by NOAA Fisheries' Southwest Fisheries Science Center, shadowed the NOAA ship Bell M. Shimadaas it transited survey stations. The gliders lingered at certain stations. One gathered observations over about 10 days compared to the ship's visit of about 2 hours. Another glider sampled a different station for 3 days.

That made a world of difference, researchers said. The gliders will likely help fulfill CalCOFI's mission of informing stock assessments vital to fisheries management.

One glider arrived at a survey station several days before the ship, sampled alongside it, and then stayed to sample for several days after the ship departed. The glider tracks zooplankton moving up and down in the water as night turns to day. It collects high-resolution shadowgraph images of the tiny organisms at the base of the marine food chain and their distribution through the water. The ship, by comparison, gathers the creatures in fine nets that lump them together with no sense of how deep or how spread out they were.

Overlooked Species Proves "Superabundant"

Fragile organisms called radiolarians-bristling with spikes-had often gone overlooked because they were destroyed in the nets, said Andrew Leising, a research oceanographer at the Southwest Fisheries Science Center. The glider images revealed they are actually "superabundant" off the California Coast, perhaps playing important roles in the marine ecosystem.

"We want to use the community of plankton to understand the oceanography of how the water is moving and how those conditions affect the ecosystem," Leising said. "Now we can truly see the whole picture, and it's even more fascinating than we realized."

CalCOFI aims to unravel how the changing marine ecosystem affects fish populations. Managers need to understand that to keep fishing sustainable, said Noelle Bowlin, a research fish biologist at the Science Center who leads NOAA's participation in CalCOFI. The program began ocean surveys in 1949 to figure out why the California sardine fishery collapsed in the days of Cannery Row, decimating fishing communities for years.

"We also want the gliders to help expand the surveys at times when we don't have ships out, especially when we perceive that conditions may be changing," Bowlin said. That may be particularly important in understanding the ocean changes that come with influences such as El Niño, which is expected to increasingly affect the West Coast this fall.

UC San Diego Professor Daniel Rudnick's laboratory also operates gliders along CalCOFI's survey patterns, some that have helped support the survey for close to 20 years. He said his California Underwater Glider Network complements ship surveys "by making some of the same measurements as the ship, but continuously, so there are no gaps in time between surveys, and with fine spatial resolution, so there are no gaps between stations."

The gliders may collect more than 50 times as many underwater profiles as survey ships when both are operating, he said.

Data Informs Fisheries Management

The goal of the combined CalCOFI data is to strengthen oceanographic models that support stock assessments for commercial fish species, said Jen Walsh, a research biologist at the Science Center who began piloting gliders to support its Antarctic research. She directed the gliders remotely from California to slip among icebergs and collect data on krill and their frigid ecosystem. That data informs management of krill fisheries, which can affect Antarctic wildlife such as penguins and fur seals.

"We realized the gliders extended our reach to help provide a more comprehensive picture of the system and how it responds to changes and pressures such as fishing," Walsh said.

For Leising, the gliders bring his research on oceanography of California full circle. As a graduate student in the 1990s, he helped develop and operate instruments to collect the kind of data on plankton and the surrounding oceanography now coming from the gliders.

The difference is that with the more rudimentary battery and computer technology at the time, the combined instruments were the size of a minivan, he said. A ship carried the monitoring unit offshore, lowering it on steel cables. "You couldn't have even envisioned what we are doing now," he said. "We're on an entirely different level."

The zooplankton imaging capabilities of the modern gliders build on a pioneering " Zooglider " designed by Mark Ohman at Scripps Institution of Oceanography at UC San Diego. The Zooglider first brought the technologies together close to a decade ago. Gliders measure roughly the size of four Scuba tanks placed end-to-end.

Gliders First Studied Antarctica

Gliders at the Southwest Fisheries Science Center first proved themselves as part of the U.S. Antarctic Marine Living Resources Program , gathering data to inform management of commercial krill fisheries. Their new application off California will help fulfill CalCOFI's similar mission of supporting stock assessments essential to sustainable fisheries management.

Leising developed AI tools that sort through hundreds of thousands of shadowgraph images. They document the species and abundance of plankton in a fraction of the time it would take him to do it on his own. He can also assemble color-coded cross-sections of the ocean from glider data illustrating the depth of a chlorophyll layer that provides the foundation for the marine food web.

The images reveal how plankton known as copepods shift vertically through the chlorophyll layer, which helps understand their role in the food web, especially as forage for fish species. Larval and newly hatched fish feed on the plankton, which vary in their nutritional content that in turn affects how fast the fish grow.

"This all helps us make a better model of how the environment affects the growth rate of fish and what that means for the larger population," Leising said. "We'll be able to routinely give managers a better idea how fish populations are changing, since we have so much more information on their entire menu."