Humans are living in a plankton world. These minuscule organisms are spread across the oceans, covering nearly three-quarters of the planet, and are among the most abundant forms of life on Earth.

But a warming world is throwing plankton into disarray and threatening the entire marine food chain that is built on them.

A year ago, NASA launched a satellite that provided the most detailed view yet of the diversity and distribution of phytoplankton. Its insights should help scientists understand the changing dynamics of life in the ocean.

“Do you like breathing? Do you like eating? If your answer is yes for either of them, then you care about phytoplankton,” said Jeremy Werdell, the lead scientist for the satellite program, called PACE, which stands for “Plankton, Aerosol, Cloud, ocean Ecosystem.”

Historically, research from ships has captured limited snapshots in time, offering only glimpses of the ever-changing oceans. The advent of satellites gave a fuller picture, but one still limited, like looking through glasses with a green filter.

“You know it’s a garden, you know it’s pretty, you know it’s plants, but you don’t know which plants,” explained Ivona Cetinic, a NASA oceanographer. The PACE satellite effectively removes the filter and finally reveals all the colors of the garden, she said. “It’s like seeing all the flowers of the ocean.”

These flowers are phytoplankton, tiny aquatic algae and bacteria that photosynthesize to live directly off energy from the sun. They are eaten by zooplankton, the smallest animals of the ocean, which, in turn, feed fish and larger creatures.It may seem implausible that a satellite orbiting high above the planet’s surface could make out microscopic organisms. But different phytoplankton have unique ways of scattering and absorbing light. PACE measures the whole spectrum of visible color and slightly beyond, from ultraviolet to near infrared, allowing scientists to identify different kinds of phytoplankton. Older satellites measured limited colors and could only reveal how much phytoplankton was underneath them, not what kind.Phytoplankton form the foundation of the marine food chain, and climate change is shaking that foundation.

Phytoplankton in the open ocean appear to be dwindling. In the early 2000s, scientists detected that enormous zones of ocean with fewer nutrients and sparser phytoplankton, known as ocean deserts, are expanding. At the same time, coastal phytoplankton blooms, especially at higher latitudes, have grown and become more frequent, according to a 2023 study. Warmer sea surface temperatures are stimulating their growth, the researchers found. These blooms are also happening earlier in the year, disrupting coastal fisheries and people’s livelihoods.

And while marine life depends on phytoplankton, sometimes it can create harmful blooms. Understanding what kinds of phytoplankton are where can help coastal residents protect themselves.

Some phytoplankton blooms grow so big, so quickly, that when they eventually decay, they deplete oxygen in the surrounding water, creating “dead zones” where nothing else can live. And some phytoplankton produce toxins that can sicken and kill fish, birds, and mammals, including humans.

Researchers estimate, conservatively, that harmful blooms cost the U.S. economy about $50 million each year through damage to public health, fisheries and coastal recreation.

In the winter of 2021, millions of pounds of oysters on the coast of Plaquemines Parish in Louisiana suddenly died, striking a major economic blow to local fishermen. Subsequent investigation revealed that toxic phytoplankton had bloomed following a storm, according to Bingqing Liu, an oceanographer and assistant professor at the University of Louisiana, Lafayette.

Liu is part of the PACE “early adopter” group, working on incorporating the satellite’s data into a model that can simulate future scenarios. If people can see toxic blooms coming, they can try to mitigate economic and environmental losses, she said.

Digging deeper

While satellites help some oceanographers zoom out to get the biggest possible picture, other researchers are zooming in, collecting plankton from the ocean and studying them under microscopes. These scientists aren’t just looking at the garden Cetinic described, but stepping into it, examining both plants and animals. And they are digging around, looking beneath the surface where satellites can’t see.

Across the North Atlantic in winter, the ocean’s garden conceals a curious phenomenon. Stretching from the United States and Canada all the way to Europe, quadrillions of tiny creatures are asleep, suspended in the ocean’s twilight zone. They are Calanus finmarchicus, a type of zooplankton, animals that drift in the ocean’s currents and tides.

In the North Atlantic, Calanus funnel energy from the sun and phytoplankton into larger animals like fish, whales and birds.

You can think of Calanus as “little batteries that are floating in the ocean,” said Jeffrey Runge, a zooplankton ecologist who recently retired as a professor from the University of Maine.

Calanus hibernate through winter, hiding from predators in the dim light of deeper waters. But in November in the Gulf of Maine, as the days shortened, the temperature dropped, and the winds and waves rose, David Fields, a zooplankton ecologist at the Bigelow Laboratory for Ocean Sciences, was out hunting these tiny creatures.

Back at the lab, after dark, scientists peered at captured Calanus finmarchicus under a microscope. The specimens had big oil sacs, full of the calorie-rich lipids that fish and right whales seek out. In experimental studies, Fields and his colleagues have found that as the temperature rises, Calanus get smaller and have less fat relative to their body size.

Fields calls the layer of sleeping Calanus the ocean’s fat layer, a valuable resource for other life. “That’s the whole reason the Gulf of Maine runs the way it does, because of that beautiful fat layer,” he said.

One of the people on the November plankton hunting trip in Maine was Amy Wyeth, a zooplankton ecologist starting a new plankton sampling and habitat monitoring program for the Maine Department of Marine Resources. The goal, she said, is to eventually give the state “a little more predictive power,” to forecast the movements of right whales and help Maine’s lobster fishery avoid entanglements with whales.

North Atlantic right whales are an endangered species, with only about 370 individuals left. They eat Calanus finmarchicus, sometimes consuming hundreds of millions of the tiny creatures every day.

The Gulf of Maine is historically a rich summer feeding ground for right whales. But in 2010, a marine heat wave began forming in this normally cold ecosystem. It started in the deep waters, where warm and cold ocean currents shifted. Then, in 2012, New England experienced unusually warm air temperatures as well.

Suddenly, there were fewer of the larger, lipid-rich adult Calanus around in the late summer and fall.

Ever since, right whales have been swimming farther north in search of more and fatter Calanus. They’ve gone to the Gulf of Saint Lawrence, where busy commercial fisheries and large high-speed ships weren’t ready for them. Many whales were struck by ships or entangled in fishing gear.

“One can make the link between relentless CO2 increase and what’s happening to the right whales right now. And what’s happening to Calanus,” Runge said. “It’s one of these really complex mechanisms of how CO2 increase and warming, the resulting warming, is affecting the ecosystems of the world.”

A fuller picture

In January, a group of European researchers called for continued support for long-term plankton monitoring programs. Since the 1930s, scientists have given commercial ships devices called continuous plankton recorders to tow and automatically collect plankton on long nets that roll up like scrolls. These methods, and many routes, have stayed consistent for decades, allowing researchers to see changes in plankton populations over time.

In the United States, NOAA has conducted plankton surveys similar to Fields’ since the 1960s, helping fisheries managers track the health of the ecosystems their industry depends on. The latest State of the Ecosystem Report for New England, produced by NOAA’s Northeast Fisheries Science Center, documented a record-high phytoplankton bloom in 2023 and also found that zooplankton in parts of the Northeast continental shelf are diversifying, a potential sign of ecosystem restructuring, according to the report. In particular, smaller, more gelatinous and less energy-rich species are increasing.

Scientists emphasize the need to keep long-running data sets going. “Monitoring really isn’t sexy science,” said Michael Parsons, a biological oceanographer at Florida Gulf Coast University. “It’s hard to keep consistent funding in place to routinely be out there collecting samples and looking at what’s there.”Enrique Montes, a biological oceanographer at the University of Miami Cooperative Institute for Marine and Atmospheric Studies and NOAA’s Atlantic Oceanographic and Meteorological Laboratory, is in the midst of analyzing plankton data from recent marine heat waves off the coast of Florida as well as the current red tide outbreak. He is also involved in national and international efforts to share and standardize data on marine biodiversity.

“We don’t really know how biodiversity is changing across the world ocean,” he said.

One way he collects data is through an underwater microscope that photographs plankton in their natural environment. He and other scientists emphasize the need to combine these kinds of local observations with satellite data.

Satellites show scientists the big, whole-ocean picture, but they have limitations. PACE has a resolution of 1 kilometer, and “telling you what happens in a 1-kilometer pixel is really different from drilling down to somebody’s backyard, which is often the information people need to know,” said Clarissa Anderson, a biological oceanographer at the University of California San Diego’s Scripps Institution of Oceanography.

Anderson is another member of the PACE early adopter group and a co-chair of the National Harmful Algal Bloom Committee, which advises Congress and other federal and state entities on these blooms.

“We’re just trying to make this seamless,” she said, “so you can go from that satellite view and drill down all the way to the very near shore: What’s happening at my pier? What’s happening at my dock?”