How a great plankton migration could pose a 'serious threat' to ocean ecosystems and the planet

Plankton are tiny – but can have a big impact on the planet.

If Earth’s ocean keeps warming, these microscopic plants and animals could move to cooler waters to survive.

Plankton are an important marine food source and also soak up carbon from the atmosphere – so this migration could have big consequences for ocean ecosystems.

Using statistical modelling, scientists in Switzerland are now predicting where plankton might end up and what this could mean as the ocean warms.

At very high temperatures above 25°C, their scenario sees plankton migrating from the tropics towards the North and South Poles.

“Plankton species from the tropics and subtropics will shift polewards and replace species that are adapted to cooler waters,” says the research team at ETH Zürich, a public research university in Zürich, Switzerland.

The researchers used global data, statistical algorithms and climate models to create distribution maps for more than 860 species of phytoplankton – plant-like plankton – and zooplankton – microscopic animals.

By overlaying these maps, they were able to see what marine plankton communities might look like in the future and where they might occur.

Plankton migration will give rise to “numerous new communities” that have never existed in these combinations before, with “unforeseeable consequences,” finds the study, led by researcher Fabio Benedetti and senior scientist Meike Vogt.

“In some areas of the ocean, we will see a rise in species numbers that may, on the face of it, seem positive. But this boost in diversity could actually pose a serious threat to the existence and functioning of well-​established marine ecosystems at higher latitudes,” Benedetti said in a statement.

As their ocean habitats change, smaller plankton could thrive, while larger plankton decline.

Because plankton are an important food source for marine creatures, this could harm fish yields, suggests the research, which was published in the journal Nature Communications.

Moreover, the role of plankton in absorbing carbon could be affected. For large marine plankton species, whose dead organisms and excrement sink faster and to greater depths than those of smaller species, the absorbed CO2 remains bound for long periods of time. If smaller plankton species replace larger ones, the transfer of carbon to the deep ocean will decrease.

Phytoplankton use photosynthesis to absorb carbon from CO2, the researchers explain, and are also a food source for zooplankton. These animal-like zooplankton in turn “nourish fish and marine creatures up to and including the blue whale,” the scientists add.

Scientists have seen evidence of plankton migration because of climate warming since the 1950s. This included an influx of tropical jellyfish – a type of zooplankton – in 2005 to Ireland, which devastated salmon farms along its coast.

Keeping Earth’s ocean healthy is the founding aim of Friends of Ocean Action, a coalition of more than 65 ocean leaders who are fast-tracking solutions to the most pressing challenges facing the ocean.

It is hosted by the World Economic Forum and led in collaboration with the World Resources Institute.

The group’s latest Impact Report shows progress in areas including marine protection, ending illegal fishing and decarbonizing shipping.