First author

Credit: G. OPPEGÅRD

The ocean will no doubt have an important role in global warming. Yet predicting its role remains a challenge without a better understanding of how marine microorganisms interact to drive carbon and nutrient cycles. On page 387, Frede Thingstad, a marine microbiologist at the University of Bergen in Norway, and his diverse team describe counterintuitive findings from an experimental Arctic ecosystem — that adding carbon to a marine food web reduces the system's total carbon. Thingstad says solving this conundrum sheds light on the seas.

Why were these findings counterintuitive?

Finding less total carbon after adding it to the system was a surprise. The individual data, from bacterial abundance to total organic carbon levels, did not tell a consistent story until we worked through the mechanisms involved. Microbial growth rates can be limited by either organic carbon or nutrients. When carbon is limiting, bacteria compete for — and immobilize — mineral nutrients, which reduces their ability to produce new organic matter, lowering the total organic carbon.

Why are marine food webs hard to study?

Marine food webs are less accessible than land-based webs. Like all microbes, marine microorganisms are difficult to see, and scientists can grow only a tiny fraction of them in the lab. We are dependent on developing techniques to determine which organisms are present and what properties they have. Although these techniques are improving, there are still many unknowns in the system that surprise us.

What research is needed to untangle marine food webs?

Rather than taking ocean measurements, we need to experiment with the system's dynamics. We used mesocosms — experimental systems holding a cubic metre of seawater — to study microbial interactions under controlled conditions. Ideally, we'd like to place them offshore to conduct replicated, real-world tests in diverse, open waters.

Has the field developed as you imagined?

Early on, I thought that mathematically modelling the entire microbial food web sounded ridiculous. Not any more. The main lesson of this work is that we can better understand basic mechanisms with models.

What do you hope to learn before you retire?

I hope to understand how microbial biodiversity is controlled in the ocean. It must be partly driven by how organisms with different life strategies optimize nutrient competition and defend against viruses or predators.