Coral reefs’ appeal to divers and nature documentaries is mainly the beautiful colors, but biologists have an additional passion for this: How could such rich life arise on the sea floor, where there are so few nutrients?
It’s called Darwin’s paradox, and that big name also fits with the complexity of the answer. Little by little, the coral reef’s secret recipe is revealed. A hurry. Our ignorance of how these ecosystems function completely hinders their protection, while they are rapidly disappearing.
We know very little about what happens in the giant oases in the marine deserts, but what we do know shows that symbiosis often plays a major role. This is a collaboration between two organisms, usually a microbe and a host. For example, the common principle is that algae use sunlight to make sugars and pass them on to animals and plants on coral reefs. But it is very difficult to say exactly how such coexistence works.
Looking at individual cells
We particularly welcome the study, which was published this week in the journal Science advances. Here, the interaction between algae and the host, the sea anemone, has been studied in detail, particularly in nitrogen recycling. On Earth, we now quickly associate this element with excess, but it is so scarce in the oceans that it is often the main barrier to ecosystem prosperity.
The researchers used a new technology with the amazing name of laser microdissection. Basically, a laser beam is used to isolate cells so that they can be seen individually under a microscope. So they saw exactly what happened when the host was supplied with sugars. The process triggered a genetic mechanism in aiptasia that produces an enzyme. This enabled the anemones to extract nitrogen from the ammonium, which could be given to the algae in return. Sure enough, they repeated the trick with anemones from the same family that survive without the help of moss. If they are given sugars, they produce the exact same enzyme.
Honestly: the host does something for the sugars they receive. Uncovering such mechanisms helps understand what symbiosis really involves, says Jasper de Guij, a marine ecologist who focuses on the role of sponges in coral reefs. “Often the idea is that microbes actually do everything,” says De Goeij. “But this host is not the host for nothing. This is really very important in this process.”
Better understanding, better expectations
The important caveat is that it is not about coral reefs. Anemones are related animals, but whether the same process also applies to stony corals has yet to be proven. De Goeij predicts that the result will 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 a boost to coral reef research. De Goeij uses the same laser microanalysis to study how sponges absorb their food. “With these technologies, you can follow the actual symbiosis at the cellular level. So you can actually see it. This is a great development,” says de Joij.
The coral-reef paradox that Darwin puzzled over has been clarified a bit more
Where do coral reefs get their biological wealth from? Darwin already asked this question, and there will be new parts of the answer.
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