Intense cooperation brings the wet desert to life

The attraction of coral reefs for divers and nature documentarians lies primarily in the beautiful colors, but biologists have an additional fascination with this: how is it possible for such rich life to occur on the seabed, where there are so few nutrients?

It’s called Darwin’s paradox, and that big name also fits the complexity of the answer. Little by little, the secret recipe for a coral reef is revealed. And there is a rush. Our ignorance of the exact functioning of these ecosystems hampers their protection, while they are rapidly disappearing.

We know very little about what happens in giant marine desert oases, but what we do know shows that symbiosis often plays a key role. It is the cooperation between two organisms, usually a microbe and a host. For example, a common principle is that algae use sunlight to make sugars and pass them to animals and plants in the coral reef. But it is very difficult to determine exactly how such a symbiosis works.

Watch individual cells

Particularly welcome is a study that was published this week in the journal Scientists progress. Here, the interaction between an algae and a host, the sea anemone aiptasia, was studied in detail, particularly in nitrogen recycling. On land, we now quickly associate this element with a surplus, but in the oceans, it is very rare and is often the main obstacle to the flourishing of an ecosystem.

The researchers used a recent technique with the spectacular name of laser micro-dissection. Basically, a laser beam is used to isolate cells so they can be seen individually under a microscope. They therefore saw exactly what happened when the host was supplied with sugars. The process triggered a genetic mechanism in the aiptasia which produced an enzyme. This allowed the anemone to extract nitrogen from the ammonium, which could be given to the algae in exchange. Certainly, they repeated the trick with anemones of the same family that live without the help of an algae. If they were given sugars, they produced exactly the same enzyme.

To put it bluntly: the host does something in exchange for the sugars it receives. Discovering such mechanisms helps to understand what symbiosis really involves, says Jasper de Goeij, a marine ecologist who focuses on the role of sponges in coral reefs. “The idea is often that microbes do everything,” says De Goeij. “But this host is not the host for nothing. It’s really very important in the process.

Better understanding, better predictions

An important caveat is that this is not coral. Anemones are related animals, but whether the same process also applies to hard coral remains to be proven. De Goeij expects the discovery to certainly help improve models that attempt to approximate processes in coral reefs and predict the effects of climate change.

The success of the method used is also an asset for research on coral reefs. De Goeij uses the same laser micro-analysis to study how sponges absorb their food. “With these techniques, you can follow the actual symbiosis at the cellular level. So you can actually see it. It’s a great development,” says De Goeij.

Read also:

The paradox of coral reefs that Darwin was already puzzled about has been clarified a little further.

Where does the coral reef get its biological richness? Darwin has already asked this question, there will be new answers.