Re: Caulerpa prolifera & biological control

March 20, 2003
From: Thierry Thibaut

Hi Bill,
I see that the biological control of Caulerpa taxifolia is still worrying people and that misunderstanding of the phenomenon and wrong ideas are still spreading on the web. In the Mediterranean Sea there is only two introduced (via man) and invasive Chlorophytes Caulerpa taxifolia and Caulerpa racemosa var. occidentalis (not coming from the Red Sea, not the other Caulerpa sp. neither the other C. racemosa variety or forms) that's all. Caulerpa prolifera is not introduced nor invasive at all. It's a common algae.
About the slugs, as far as I know the only people who are doing reserach on this subject are from Nice (my lab), with international collaboration that's all. So I feel I should clarify the ideas about what was done.

We are following guidelines made by the International Council For the Exploration of the Sea on the introduction of biocontrol agents into the marine environment, also the FAO's guideline on the same topic. These guidelines are very strict about the procedure of evaluation of the biocontrol agent.

First find local predator:
Oxynoe olivacea and Lobiger serradifalci. O. olivacea is a bad competitor and L. serradifalci disperses the algae (ONLY this species) for further details see Thibaut & Meinesz 2000, Zuljevic et al 2001 (You can find the entire references in the species page of the SeaslugForum [see Thierry's earlier message]. So the guidelines say if these species are not suitable, and they are not for sure, look for allochtonous species: Elysia subornata. First look for dietary switching if there is a problem, eliminate it, parasites introduction the same,... (see details in Thibaut et al 2001). The guides say test the efficiency BUT not in the open sea because it will be a definitive introduction, so do mesocosm experiment or modelling (we did modelling, see Coquillard et al 2001).
That's all the work done on this subject. We are perfectly aware about the risks using an allochtonous species. These risks should be compared with the risks and impacts induced by the invader, ie C. taxifolia and C. racemosa. Which are huge. This is called the Risk-Benefit analysis. Impacts made by the caulerpas already recorded on the ecosystems and economy are much higher that the hypothetical risks of the introduction of the slugs. We perfectly know the mistake made with biocontrol agent on land and so on. Our works were presented in most of the most important meeting of expert in the fields of biocontrol and invasive species and all said that we made a good job, respecting the guidelines,... But if someone give me SCIENTIFIC PROOFS that we made mistake or we missed something, which is possible, we will assess again the biocontrol agent.

So we made our job of scientists and tried to find a solution because there is NO more solution in the Mediterranean Sea. Now it is a political problem. I think that people should be more afraid by "legal" introduction without following the procedures made by National organisation for aquaculture, fish farming...IT IS A MESS, for example in Thau lagoon in South of France there is more Japanese weeds than Mediterranean species... On terrestrial ecology some famous French organisation are importing freely and testing biocontrol agents without all the precautions required and nobody care. I do not understand what's wrong with Caulerpa, is there something special, I really need to know, because there many other teams working on marine biocontrol and I never see any strange comments on their works.

Thibaut, T., 2003 (Mar 20) Re: Caulerpa prolifera & biological control. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Thierry,
I certainly wasn't making unfavourable comments on your science or that of your laboratory. I often refer to your work and recommend it to colleagues and students. Without diligent studies like yours then there is nothing to discuss. Like you, I have seen the disastrous results of many careless and sometimes stupid introductions of foreign organisms and so try, where possible, to suggest a cautious approach. The point I was trying to make is that I know of no evidence to show that any species of sacoglossan eats enough of its food plant to control the growth or reproduction of that food plant. [Cynthia Trowbridge's message was supporting this point.] Until such a 'wonderslug' is found, there seems to me no point in introducing a foreign sacoglossan anywhere there is a Caulerpa outbreak. You mention a risk/benefit analysis. It seems to me that until a sacoglossan population can be shown to seriously reduce a Caulerpa outbreak, then there is no benefit to the environment and therefore no risk is acceptable.

Unfortunately these outbreaks are not just confined to the Mediterranean and headline grabbers - both scientists in search of grants, and politicians, - can say and suggest some very stupid things. The possibility of biological control by newsmedia is very frightening.
Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Mar 20). Comment on Re: Caulerpa prolifera & biological control by Thierry Thibaut. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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