Plankton are the backbone of the ocean and may not survive what is coming

Dino Grandoni
| Washingtonpost

They drift aimlessly at sea, sucking in sunlight from the air 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 largest whale depends on them for their livelihood.

Yet these tiny organisms – called plankton – may not thrive in rapidly warming oceans, according to a pair of new studies. The decline of these microscopic creatures will endanger large swaths of marine life in the coming decades if nothing is done to curb human-induced climate change.

“When the little things disappear, the food disappears – for the small fish, and then for the bigger fish, for the marine mammals and for us,” says Daniela Schmidt, a climate scientist at the University of Bristol in England, who co-wrote one of the two articles published on Wednesday in the journal Nature.

Each of the two studies takes a different approach, but comes to the same surprising conclusion: plankton, many of which form the basis of marine food chains, are under siege. The research underlines one of the many ways in which oceans are increasingly under attack, with potentially dire consequences for people who rely on the seas for food.

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

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To assess the future impact 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 small shells that fall to the seafloor when they die.

While many plankton have become accustomed to the increase in temperatures from the height of the last ice age 20,000 years ago to the present, plankton biomass will decline by more than 10 percent if the world rises 3 degrees Celsius above pre-historic temperatures by the end of the century. industrial level is warming, researchers found.

It’s a rate of warming that researchers say plankton simply cannot withstand. “The last deglaciation lasted several thousand years,” Schmidt said. “The same amount of warming is now taking place over a period of a hundred years.”

Plankton decline is already underway.

In the second study in Nature, plankton ecologist Sonia Chaabane and her colleagues combed through 80 years of data on plankton collected by nets, traps and other instruments around the world.

Examining almost 200,000 samples, the team found that the abundance of foraminifera has already fallen by almost a quarter since the 1940s, with many species migrating from the equator to 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 big, very fast – and will continue to be fast, we think,” she added.

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

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

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Climate change threatens plankton in several ways. The warming is choking the ocean circulation that brings nutrients from the depths to the surface. The buildup of carbon dioxide dissolved in water makes the oceans more acidic, making it harder for foraminifera to build their shells.

Unlike sharks and squid, plankton cannot propel themselves through the water, making migration to cooler habitats difficult. “They can float,” Chaabane said, “but they can’t swim against the current.”

Just a 10 percent drop in plankton could cause a domino effect that leads to a decline in populations of fish and other larger marine animals further down the food chain, according to Schmidt. “It would just be cruel,” she said. “It doesn’t sound much, 10 percent. But it is a huge change.”

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

Even for those who don’t eat fish, plankton is crucial to preventing climate change from getting worse than it already is. When foraminifera form their shells, they bind carbon with calcium to create their building material. After they die, the shells fall to the seabed, banishing the carbon from the atmosphere forever.

Plankton is certainly not the only marine species in danger. More than 40 percent of reef-building corals are at risk of extinction, according to a report also released Wednesday by the International Union for Conservation of Nature.

As temperatures rise, the coral fades to a ghostly white after expelling the symbiotic algae that provide them with food. Reefs from Fiji to the Florida Keys have recently been devastated by a massive global bleaching event.

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

The wave of research into marine life comes as diplomats meet in Azerbaijan this month at a UN climate summit. The talks are aimed at keeping countries on track to keep temperature rises below 1.5 degrees Celsius by the end of the century. Countries can slow warming by reducing greenhouse gas pollution.

But right now the world is very shy of achieving that goal.

“Cutting emissions is really the only way we can stop warming,” Swadling said.