The impact of global warming on plankton could have potentially serious consequences for marine life

The strange box that scientists remove from the sea and leave on the deck of the ship could be a spaceship dreamed of by a child. But when Clare Ostle examines its contents, she finds some of the most important creatures on Earth: plankton.

The device, called the Continuous Plankton Recorder (CPR), has been used since the 1930s to allow researchers to better understand these marine organisms.

Plankton brings together aquatic species carried by the current, animals such as jellyfish in zooplankton and plants in phytoplankton, as well as bacteria and viruses.

It forms the basis of the marine food chain, produces much of the oxygen we breathe, and plays an essential role in the carbon cycle.

“The most important thing we see is global warming,” explains Ostle, coordinator of the Pacific CPR Survey, and this has potentially serious consequences for marine life and humans.

The study showed a movement of plankton towards the two poles in recent decades, as ocean currents change and many marine animals head to colder areas.

Plankton that live in warmer waters are replacing that of cold waters, often with different seasonal cycles, forcing the species that feed on it to adapt or leave.

“The big concern is when the change is so rapid that the ecosystem cannot recover,” Oster tells AFP. The increase in the temperature of the oceans can cause “the collapse of entire fishing grounds”, he explains, and recalls that almost half of humanity has fish as their main source of protein.

Produces oxygen and stores CO2

Phytoplankton, meanwhile, help the oceans produce half the oxygen on Earth and, at the same time, store at least a quarter of the CO2 emitted by fossil fuels burned by humans.

When plankton and their predators die and sink to the bottom of the sea, sand they carry with them the carbon they stored.

But climate change is putting pressure on this ecosystem, with the increase in sea temperature, the decrease in nutrients that come from the bottom to the surface and the increase in the acidification of the water.

The warm-up “It is exposing oceanic and coastal ecosystems to conditions unprecedented for centuries and millennia, with consequences for the plants and animals that inhabit the world’s oceans”, say the experts of the Intergovernmental Panel on Climate Change (IPCC) of the UN, in the draft of a report to be published in 2022, in which they warn of its “growing impact on marine life.”

The average biomass of plankton, which measures the weight or total number of these creatures on the planet, is predicted to is reduced between 1.8% and 6% depending on the level of greenhouse gas emissions and climate change.

But due to its high importance, even a modest reduction in plankton can affect the marine feeding cycle and lead to a reduction in life in the oceans of between 5% and 17%.

There could also be “changes in the carbon cycle and carbon sequestration as our plankton changes” and smaller plankton could absorb less C02, says expert Abigail McQuatters-Gollop of the University of Plymouth in southwest England.

As world leaders prepare to meet at COP26 in Glasgow, this is a prime example of how accelerating human impacts are destabilizing the intricate ecosystems that support life.

Think small

The solution to this question is not as easy as planting trees, McQuatters-Gollop notes.

But sustainable fishing, reducing pollutants and reducing CO2 emissions can help improve the health of the oceans.

In the past, environmental protection has focused on “things big, beautiful or with direct monetary value”, such as whales, turtles or cod, he says.

But all of this depends on plankton. Like land plants, phytoplankton need nitrates, phosphates, and iron to grow.

But an excess of nutrients can cause environmental disasters, like this summer in Turkey, when the coasts were invaded by “sea mucus”, blocking the sunlight and depriving the underwater flora and fauna of oxygen.

Plankton efflorescence, visible from space, can be fueled by sandstorms or volcanic eruptions. This natural phenomenon has inspired David King, founder of the Climate Repair group in Cambridge, to fertilize plankton by dispersing iron on the surface of the water.

His theory is that this would not only help absorb more C02, but lead to an increase in life in the ocean, including eventually helping increase whale populations that have been devastated by hunting.

Much to learn

More whales equates to more droppings, which are packed with the nutrients plankton need to flourish, and King hopes it can restore a “wonderful circular economy” in the seas.

A pilot project will test this technique in an area of ​​the Arabian Sea carefully sealed in a “huge plastic bag”. But King acknowledges that the idea raises unintended consequences: “We certainly don’t want to deoxygenate the oceans and I’m pretty sure we won’t,” he says.

Ocean organisms have photosynthesized for billions of years, long before land plants. But we still have a lot to learn about them.

It wasn’t until the 1980s that scientists named the planktonic bacteria prochlorococcus, which is now considered the most abundant photosynthesizer on the planet.

Scientists have used the data obtained by the Continuous Plankton Recorder to look back and track climate changes. It has also played an important role in the recognition of microplastics that pollute the seas.

Ostle used the records of these ships to show that “macroplastics” such as shopping bags were already in the seas in the 1960s.

From the boat in Plymouth, the water appears calm as sunlight glides across its surface. But every drop is full of life.

“There is a whole galaxy of things happening down there,” says the scientist. (I)