Betcha a nickel you don’t know what plankton is. Less than 9 percent of college-educated Americans do, according to a very unscientific survey of semi-randomly selected people I happen to know (n=12). That’s a shame, because plankton is an incredibly important part of the marine ecosystem, and it’s behaving in increasingly weird ways. A recent study from researchers at Stanford University shows that the growth rate of a type of plankton called phytoplankton in the Arctic Ocean has increased 57 percent between 1998 and 2018, with uncertain implications for animals higher up the food chain (which is most of them, including us).
Plankton, for the 91.7 percent of you who probably don’t know, is not a specific type of creature. It’s any marine organism that drifts with the currents rather than swimming under its own power. This is a very broad category that includes mostly single-celled organisms, but also animals, such as krill and jellyfish. There are also species that are plankton at some stages of their lives but not others. Think of fish eggs or starfish larvae, which cease to be plankton once their inhabitants hatch or grow large enough to move on from their drifter lifestyle.
Plankton that must eat to survive are called zooplankton, while the plant-like plankton that contain chlorophyll and generate their own energy are phytoplankton. Through photosynthesis, they combine the sun’s energy with carbon dioxide taken from the atmosphere and other nutrients to grow and multiply. Thus, phytoplankton, such as algae, form the base of the ocean food chain, and a large supply of them is vital to the health of any ocean ecosystem. A crude but mostly accurate way of thinking about the marine food web would be as follows: Phytoplankton typically get eaten by zooplankton, which typically get eaten by small fish, which then typically get eaten by bigger fish and mammals, and so on.
It would seem like good news, therefore, that the Arctic Ocean is producing larger and larger phytoplankton blooms. By calculating decades of data taken from satellite imagery and collected from ice-breaking ships, the Stanford researchers have found that productivity at the base level of this ocean ecosystem has increased by more than half over 20 years. This is an incredible surge in phytoplankton—one that provides more food and increases the ocean’s uptake of carbon dioxide, a greenhouse gas. All of this sounds like it could be a boon for both biodiversity and climate change mitigation.
But everything isn’t so rosy. The initial expansion of phytoplankton in the Arctic was a symptom of climate change, not a potential cure. The Arctic is warming twice as fast as the rest of the planet, and melting sea ice has provided more open water for plankton to grow in for longer amounts of time during the year.
Now here comes the weirdest part. According to the researchers, sea ice loss is no longer continuing to drive the Arctic plankton boom. Rather, an influx of nutrients into the Arctic Ocean—coming in from other oceans, the researchers suspect—is allowing the phytoplankton to grow more prolifically in the same amount of water, creating what the scientists call “a thickening algae soup.”
Sounds delicious, especially if you’re zooplankton. But this soup comes with a side of several complications. Healthy food webs depend on more than sheer volumes of food. For instance, the ways in which species interact and the timing of those interactions can be crucial, and scientists have previously documented dramatic shifts when Arctic phytoplankton bloom. A larger amount of food isn’t better if it comes at a time when the ecosystem’s other members aren’t able to eat it. Back in 2010, a study showed that phytoplankton were becoming available 50 days earlier in the spring than they historically should have been. That’s a problem because the marine ecosystem is synced to the beginning of algae season. Zooplankton populations peak shortly after the phytoplankton bloom, taking advantage of the bounty, and small fish don’t come in to feast until after that. Disruptions in this chronology can throw the relationships between some species completely out of whack, potentially affecting their ability to eat, breed, and survive, and influencing what fish stocks might be available at what times.
“We knew the Arctic had increased production in the last few years, but it seemed possible the system was just recycling the same store of nutrients,” says Kate Lewis, lead author of the new study, in a press release. “Our study shows that’s not the case. Phytoplankton are absorbing more carbon year after year as new nutrients come into this ocean. That was unexpected, and it has big ecological impacts.”
Furthermore, the authors note, any increase in the Arctic’s ability to remove carbon dioxide from the atmosphere is essentially small potatoes when it comes to warding off climate change. “[The Arctic] is taking in a lot more carbon than it used to take in,” says senior author Kevin Arrigo, “but it’s not something we’re going to be able to rely on to help us out of our climate problem.” Together, all of the world’s oceans absorb somewhere around 30 percent of the carbon dioxide we release through the burning of fossil fuels. The Arctic does its part, but given the current high rates of global emissions, it won’t be enough. This carbon absorption also comes with the steep costs of ocean acidification, which has its own set of devastating impacts on ocean life, including on plankton.
What’s taking place in the Arctic Ocean is another example of global weirding—strange things happening to our planet triggered by humanity’s burning of enormous quantities of fossil fuels. With their thickening soup, phytoplankton are sending a message that big changes are afoot. We’d be wise to pay attention to the little guys.
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