A Telescope to Peer into the Vast Ocean

Twenty-five years ago, the Hubble Telescope was launched to look out to the vast darkness of outer space. It captured images of the multitudes of previously unknown stars, galaxies, and clouds of matter, literally expanding the boundaries of human vision and knowledge.

At about the same time, Cabell Davis, a biologist at Woods Hole Oceanographic Institution (WHOI), was thinking about how humans could expand their view into the vast darkness of inner space. He spearheaded development of a remarkable instrument to capture images of the multitudes of tiny, unseen life in the ocean—plankton. The instrument, the Video Plankton Recorder, is about to make a historic voyage, journeying almost 8,000 miles across the Pacific Ocean, to illuminate an unexplored universe of plankton.

Plankton is a catchall term (from the Greek word for “drifter”) that includes bacteria and other microbes, single-celled plants, tiny animals, jelly-like animals, and larvae. The vast majority of marine animal species are plankton for part or all of their lives.

Individually small, plankton are collectively mighty. Single-celled algae produce half the oxygen in Earth’s atmosphere. Abundant plant and animal plankton are the heart of the food webs that sustain fish, seabirds, marine mammals, and eventually people who depend on seafood. A key question is how will plankton and ocean ecosystems be affected by ocean conditions that are rapidly changing today. Excess carbon in the atmosphere from fossil fuel burning is being absorbed by the ocean and lowering its pH. Ocean temperatures are also warming, and circulation patterns may shift.

To determine how plankton populations might change, scientists need baseline information about today’s ocean from the smallest scale of the individual plankter to the full ocean scale. Fundamental information about which plankton live where, when, and under what conditions has remained out of our grasp because of the difficulties of finding, identifying, and counting such small organisms in such large ocean areas.

Birth of the VPR

Traditionally, scientists sampled plankton with towed nets, but nets are blunt instruments, mixing the plankton and damaging ubiquitous fragile forms. Moreover, nets capture merely a snapshot of plankton in a particular time and place, often missing patches of plankton, which are unevenly distributed through the sea. The result has been underestimates of plankton abundances.

To overcome these problems, Davis, fellow WHOI biologist Scott Gallager, and other WHOI engineers created the Video Plankton Recorder, or VPR, in the 1990s. Essentially, it is an underwater microscope, with a strobe and camera, that’s towed behind a ship. It takes rapid-fire images of the plankton passing through a small area, creating a running video instead of a few snapshots.

“We have two main systems now,” Davis said. “One, the battery-operated Digital Autonomous VPR, can go down to 1,000 meters, and you can tow it at 2 to 4 knots. It records images on a hard disc in the unit underwater. The other, the fast-tow VPRII, will go 10 knots. It’s like a little underwater airplane that flies on the end of a kilometer [0.6 miles] of cable. It undulates automatically up and down in the water, images an area about the size of your little finger, and takes 30 pictures a second. It has onboard flight control. It’s like an engineer’s dream toy! And we get live images and data—the instant feedback is fantastic.”

Across the Atlantic

In 2003, Davis and WHOI engineer Fred Thwaites, who designed the body of the VPRII, towed it 3,000 miles through the Atlantic, continuously sampling across an ocean basin for the first time and demonstrating the instrument’s ability to collect plankton data. The ship steered through warm and cold eddies, based on eddy locations emailed to the ship by WHOI scientist Dennis McGillicuddy. The VPR unveiled unexpected abundances of colonial bacteria called Trichodesmium, which have the ability to convert nitrogen gas into organic nitrogen, supplying an essential nutrient for ocean life.

Melissa Patrician, a WHOI research associate and Ph.D. student at State University of New York, Stony Brook, is using Atlantic VPR data to study plankton aggregations that may attract and supply food for whales, especially the endangered North Atlantic right whales. These data were collected on a second transatlantic VPRII tow, during the maiden voyage of the Schmidt Ocean Institute’s research vessel Falkor, from the United Kingdom to Woods Hole.

“I don’t think there’s a way to look at the patch dynamics—how, where, and when plankton patches form and disperse—without using an instrument like the VPR,” Patrician said. “I’m hoping we can have a better understanding of how currents and other factors are affecting patch formation, so that we can make predictions about where and when right whales may feed, because they’re so endangered, and management is really important for the species.”

“Understanding the causes and distribution of plankton patches is critical for understanding the entire marine food web and the ways mass and energy are used in the ocean ecosystem,” Davis said.

Across the Pacific

This month, Thwaites, Patrician, and WHOI researcher Phil Alatalo will conduct another first-time VPR exploration—across the Pacific, while Davis collaborates from his lab ashore. In February and March, with support from the Dalio Explore Fund, they will sample on the research ship Alucia, from the Marshall Islands to Panama. They will tow a high-speed VPR that will take color images every six inches over 7,767 miles.

The expedition will yield the first high-resolution data on how plankton species and abundances are distributed across the Pacific, and how plankton populations are related to environmental factors and currents. The team will also focus on links between plankton and eddies—large masses of water spinning like a whirlpool and moving through the ocean—which can bring up nutrients from deep water to the surface and fertilize plankton blooms. The scientists will once again consult with McGillicuddy and WHOI research associate Valery Kosnyrev to obtain satellite data along the way to locate eddies in progress and adjust the cruise track to cross them.

“This cruise will shed new light into the micro-world of the plankton across the vast Pacific Ocean,” Davis said.