Plankton are the backbone of the ocean — and may not survive what’s coming

They drift aimlessly at sea, soaking up sunlight from the sky and nutrients from the deep. Often invisible to the naked eye, these tiny invertebrates form the hidden backbone of ocean ecosystems. Everything from the smallest fish to the biggest whale depends on them for sustenance.

Yet these tiny organisms — called plankton — may be unable to thrive in the rapidly warming oceans, according to a pair of new studies. The decline of these microscopic creatures puts huge portions of marine life at risk in the coming decades if nothing is done to curb human-caused climate change.

“If the small things disappear, the food disappears — for the small fish, and then for the bigger fish, for the marine mammals and for us,” said Daniela Schmidt, a climate scientist at the University of Bristol in England who co-wrote one of the two papers published Wednesday in the journal Nature.

Each of the two studies takes a different approach, but they come to the same startling conclusion: Plankton, many of which form the base of marine food chains, are under siege. The research punctuates one of the many ways oceans are increasingly under assault, with potentially dire consequences for humans who rely on the seas for food.

Any drop in plankton levels will have “cascading effects through marine ecosystems,” said Kerrie Swadling, an ecologist at the University of Tasmania who was not involved in the research.

To assess future impacts of warming waters on plankton, Schmidt and her colleagues turned to ancient changes. The team analyzed an extensive fossil record of a type of plankton called foraminifera, which leave behind tiny shells that fall to the seafloor when they die.

While many plankton acclimated to the increase in temperature from the height of the last ice age 20,000 years ago to today, plankton will decline in biomass by more than 10 percent if the world warms by 3 degrees Celsius above preindustrial levels by the end of the century, researchers found.

It’s a rate of warming that researchers say the plankton simply cannot withstand. “The last deglaciation took several thousand years,” Schmidt said. “The same degree of warming is now happening over 100 years.”

The decline in plankton is already underway.

In the second study in Nature, plankton ecologist Sonia Chaabane and her colleagues combed through eight decades’ worth of data on plankton collected with nets, traps and other instruments around the world.

Scrutinizing nearly 200,000 samples, the team found the abundance of foraminifera has already dropped by nearly a quarter since the 1940s, with many species migrating away from the equator and deeper in the water column to survive.

“We are not sure that the migration would be enough for them,” Chaabane said. “The change is very, very huge, very fast — and it will continue being fast, we think,” she added.

Michal Kucera, a micropaleontologist at the University of Bremen who was not involved in the two papers, noted there are lots of challenges to understanding plankton. Foraminifera, for instance, are only one type of plankton, and the researchers’ methods for collecting them have changed over time.

Still, he said the results should be taken seriously. “No matter where and how we look, the plankton of today is already not what it used to be,” he said.

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Climate change threatens plankton in a few different ways. Warming stifles ocean circulation that bring nutrients from the deep to the surface. The accumulation of carbon dioxide dissolved in water renders oceans more acidic, making it harder for foraminifera to build their shells.

Unlike sharks or squids, plankton cannot propel themselves through the water, making migration to cooler habitats difficult. “They can float,” Chaabane said, “but they cannot swim against the currents.”

Just a 10 percent drop in plankton could cause a domino effect leading to declines in populations in fish and other larger sea creatures down the food chain, according to Schmidt. “It’d just be brutal,” she said. “It sounds little, 10 percent. But it is a vast change.”

While seafood is a luxury in many places, she added, “there are some parts of the world where the food from the ocean is the primary source of protein.”

Even for those who forgo eating fish, plankton are crucial for preventing climate change from getting even worse than it is. When foraminifera form their shells, they bind carbon with calcium to make their building material. After they die, the shells fall to the seafloor, locking that carbon out of the atmosphere for eons.

Plankton are hardly the only marine creatures at risk. Over 40 percent of reef-building corals are at risk of going extinct, according to a report also released Wednesday by the International Union for Conservation of Nature.

As temperatures rise, coral fade to a ghostly white after expelling symbiotic algae that provide them food. Reefs from Fiji to the Florida Keys were recently devastated by a vast global bleaching event.

“They can’t run away,” said Beth Polidoro, an Arizona State University conservation scientist who coordinated the work on coral. “They’re stuck to the ground.”

The flurry of research on marine life comes as diplomats meet this month in Azerbaijan at a U.N. climate summit. The talks are meant to keep nations on track to holding temperature increases below 1.5 degrees Celsius by the end of the century. Countries can stall warming by reducing greenhouse gas pollution.

But right now the world is well shy of reaching that goal.

“Limiting emissions is really the only way that we can overturn warming,” Swadling said.