Chemistry and the Natural Defences of Coral – ITW with Bernard Banaigs

© Vincent Hilaire / Tara Expeditions Foundation

Biologists, oceanographers, technicians – 70 researchers are relaying each other aboard the schooner during the Tara Pacific expedition. Among them, 2 chemists have joined this leg – an unusual one in the general protocol of the expedition. Chemists are rare. Bernard Banaigs, researcher at the INSERM, explains the very specific mission dedicated to biodiversity being conducted in the Bismarck archipelago, Papua New Guinea (PNG), where his studies focus especially on sponges. He marvels at the profusion of marine life in the region, and explains his goal: to better understand the invisible but “constant chemical fight” that’s happening underwater. Bernard Banaigs answers our questions.


How can we evoke the work of chemists in the Tara Pacific expedition ?

Before talking chemistry, I’ll try to show that this field is not really so complicated. I’m always fascinated by what I see underwater and especially here, where we observe a great biodiversity covering the substratum almost totally. Corals, gorgonians, hydrozoans, ascidians, sponges, soft corals, etc. Not a square centimeter is left bare! The consequence of this richness is a competition for space. Most of these marine organisms lay eggs, which become swimming larvae, which then need to find a surface where they can settle and develop. This animal life permanently fixed on a substratum has no equivalent on land. These animals have neither eyes nor ears, so they’ve had to develop defensive strategies to protect themselves from predators, competitors, colonizers, and even UV rays.
 Anne-Sophie_zone_de_Kapepa@Jonathan_Lancelot copie

Plongée lors de la mission “Biodiversité” menée en Papouasie-Nouvelle-Guinée – © Jonathan Lancelot / Fondation Tara Expéditions 


Chemical defenses?

Exactly. Take the example of UV rays. On land, when we want to protect ourselves from the sun, we just move into the shade. But the corals living in the first meters below the surface can’t move. They’ve had to develop anti-UV substances. As a chemist, this is what I’m trying to understand: How do all these organisms protect themselves? I’m interested in all their defenses: chemical protections, toxic or bitter-tasting substances that will inhibit the behavior of neighboring competitors.


Can a single organism secrete several chemical substances according to what it wants to protect itself against?

Yes, let’s take the example of corals. Those present in shallow depths bio-synthesize substances that will filter UV rays. They also produce other molecules to protect themselves from colonizers. If a sponge larva settles on a coral and proliferates, the coral could die from suffocation.


Why focus on these molecules?

I’m very interested in species that defend themselves effectively. These are the ones I harvest. Back in the laboratory, I extract and study the chemistry of their molecules. Here in Papua New Guinea, we can hope to find a new “chemo-diversity” associated with this exceptional biodiversity. The last step, as far as I am concerned, in the field of chemical ecology, is to determine “who does what”, to understand the function of each molecule. Are these molecules responsible for anti-predation or anti-fouling activities*? What especially fascinates me is to understand the role of molecules produced in the environment.


4 Paysage_invertebres_Anne_Sophie@Jonathan_Lancelot
Paysage d’invertébrés marins en Papouasie-Nouvelle-Guinée, sur le site d’Anne Sophie – © Jonathan Lancelot / Tara Expeditions Foundation


Molecules that can then be reproduced in the laboratory and used for human health or in other fields?

In fact I’m establishing a link between basic and applied research. With this question in the background: what are the key molecules, those that have major roles in the ecosystem? For me, it’s not a question of cataloguing all existing molecules under water. From the moment I show that a certain molecule is active in the environment, I wonder about its potential use in human health, in the field of bio-pesticides or anti-fouling.


It’s about finding commercial uses for these molecules?

Yes. Let’s take the example of anti-UV molecules produced by corals. In the coming years, sun-screen lotions that incorporate these same molecules, but synthesized in the laboratory, will be sold commercially. 50 to 60% of the medicines found in pharmacies come from natural origins! Aspirin for example, comes from a molecule contained in the bark of the willow tree. Research on marine molecules started recently — in the 1960s — and the marine environment offers certain molecules that have no equivalent on land. The potential is immense.


Noëlie Pansiot

* Anti-fouling activity: use of biocides to prevent aquatic organisms from attaching themselves to a surface (usually the hulls of ships or other immersed objects)

Articles associés