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Microscopic foraminifera – likely winners in tomorrow’s increasingly deoxygenated oceans

Research equipment on boat at sea. Photo.
In the study, the researchers analysed foraminifera brought up by drilling into the ocean floor. Photo: Helena L Filipsson.

They are called foraminifera and have lived in the world’s oceans for 545 million years. A research team has established in a new study that some species of this protist will probably cope swimmingly even in a climate-impacted future. This is due to their ability to respire nitrate.

One consequence of climate change is higher water temperatures and reduced oxygen levels in the world’s oceans. This is bad news for almost all organisms, as the majority breathe oxygen, i.e. use oxygen and glucose in cellular respiration to produce energy. However, there is one group that in all likelihood will thrive in the future. Called foraminifera, they are single-cell microorganisms that can be found in almost all marine environments. What distinguishes these tiddlers, which are as small as a grain of sand and have a shell, is their ability to respire both oxygen and nitrate. In a new study, published in the research journal Science Advances, an American-Swedish research team has mapped the gene expression and respiratory preferences of two species of foraminifera.

“In the study we can establish that the species in our experiment almost always chose denitrification regardless of the oxygen level in the sediment and bottom water – even though this produced less energy”, says Helena Filipsson, geology researcher at Lund University.

microorganism. Photo.
Microscope image of the foraminifera "Nonionella stella". Photo: Inda Brinkmann.

Foraminifera are important in the marine carbon cycle, as they produce large amounts of calcium carbonate. They also help to maintain the water chemistry balance.

“In addition, they are food for higher organisms. In the wider scheme of things you can say that foraminifera, despite their modest size, are very important for the world’s oceans”, says Helena Filipsson.

The ancient microorganisms are of interest to the research community, as they can be preserved in the bottom sediment for many millions of years. They can therefore be used as a type of “mini-dictaphone” to extract information on the marine climate of the past. By analysing foraminifera brought up by drilling into the ocean floor, researchers gain important information about how water temperatures and salt and oxygen levels have changed throughout history.

“It is important to understand how foraminifera function and how they will respond to future climate change. There is much to suggest that certain species will be able to adapt effectively to reduced oxygen levels and will be a potential winner when sea floor dead zones and oxygen depletion spread”, says Helena Filipsson.”

Besides Lund University, the following universities and organisations took part in the work: Woods Hole Oceanographic Institution, Harvard University and the University of Rhode Island.

Read the study – sciencemag.org