Global warming will dramatically reduce the population of critical communities of plankton

By Georgia Lambert via SWNS

Global warming will drive critical communities of plankton polewards - threatening the underwater biodiversity of ocean ecosystems, warns a new study.

The ocean is teeming with microscopic plants and animals, known collectively as plankton.

Each individual organism is tiny, but as a whole, the community delivers important ecosystem services. For example, plant-like plankton, known as phytoplankton, rely on photosynthesis to withdraw carbon from carbon dioxide, making them a key driver of the oceanic carbon cycle.

Phytoplankton is also a food source for a different type of plankton derived from small crustaceans, called zooplankton. These organisms are eaten by fish and marine creatures as big as the endangered blue whale.

However, as the climate heats up and the ocean temperatures rise, researchers expect to see significant changes in global plankton distribution.

But to date there have been hardly any studies investigating where different species of plankton might thrive in the future.

Now an integral part of that knowledge gap has been filled thanks to a research team led by Dr. Fabio Benedetti and Dr. Meike Vogt in Nicolas Gruber’s group at ETH Zurich.

The research team put together a global dataset, designed to create distribution maps for more than 860 species of phytoplankton and zooplankton based on various algorithms and climate models.

They then used these maps to determine what plankton communities might look like in the future and where they might occur.

Benedetti and his colleagues showed that the diversity of both Phyto and zooplankton will be expected to increase across many regions in the future because warmer water generally tends to promote a more diverse breeding ground.

However, if the temperature were to rise above 25 degrees Celsius, the phytoplankton would continue to increase, while the zooplankton diversity would decrease.

When this happens, it will lead to a reduction in zooplankton numbers within the tropics.

According to the research, plankton species from the tropics and subtropical regions will shift polewards and will eventually replace species that are adapted to cooler waters.

The outcome of these events will likely cause murky waters and scientists will observe the inevitable rise of new communities that have never existed in these conditions before, a convergence of species that do not occupy the same habitat, and whose relationships are not clearly aligned.

The scientific team expects to see the most significant changes in oceans in high and temperate latitudes that are crucial for carbon dioxide fixation and fisheries.

Study lead author Dr. Benedetti said: “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.”

Plankton also plays an important role in driving ocean carbon fixation forwards. For example, the Arctic Ocean is currently home to phytoplankton that are larger than those in tropical seas. Many of them have shells and their excretions are larger and heavier.

As a result, both dead organisms and their excrement sink faster and to greater depths before the carbon they contain is decomposed back to carbon dioxide.

When dissolved in deeper waters, this carbon dioxide remains trapped in the depths for long periods of time due to the slower circulation of the ocean depths.

In the event of smaller species replacing larger ones, this critical transfer of carbon to the deep ocean will decrease.

However, scientists cannot say exactly how significant these effects will be.

Benedetti explained: “The only thing we can determine right now is how important certain areas of the ocean are today in terms of different ecosystem services and whether this provision of services will change in the future.”

Jellyfish, another type of zooplankton, are also migrating northwards.

In 2005, Ireland detected a huge influx of tropical jellyfish, which devastated salmon farms along the coast.

Co-author Dr. Vogt added: “Events like this show that shifts in plankton distribution are already well underway.”

The findings were published in the journal Nature Communications.