Caulerpa taxifolia in the Mediterranean


Neville Coleman - World of Water.

The alga Caulerpa taxifolia has been introduced into the Mediterranean, where it has reached pest proportions in many areas. There have been proposals to introduce species of sacoglossan opisthobranchs in to the Mediterranean in an attempt to control its spread.

See messages below discussing this topic.
See Killer Algae.
See C. taxifolia - reports from southeastern Australia.
See Caulerpa taxifolia - an essay
See Lobiger serradifalci feeding on C. taxifolia.

Authorship details
Rudman, W.B., 2000 (July 16) Caulerpa taxifolia in the Mediterranean . [In] Sea Slug Forum. Australian Museum, Sydney. Available from

Related messages

Re: Eggs on Caulerpa taxifolia

December 20, 2003
From: Kathe R. Jensen

Dear Bill and Jeannie,
Re Jeannie's photos:
I agree with you that the top egg mass is probably that of a sacoglossan - in fact, I will venture a guess at Oxynoe olivacea. The yellow marks on the Caulerpa frond look exactly like feeding marks of Oxynoe. And since Oxynoe olivacea occurs on Caulerpa taxifolia in Sicily, I guess they could also be found on that alga in Elba.

I have no guesses about the other egg masses.


Jensen, K.R., 2003 (Dec 20) Re: Eggs on Caulerpa taxifolia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Kathe,
Bill Rudman

Eggs on Caulerpa taxifolia

December 19, 2003
From: Jeannine Dietz

Dear Bill,
I'm working on the green algae Caulerpa taxifolia around the Island of Elba in the Mediterranean Sea. Last year in August I found some gastropod eggs on fronds of Caulerpa taxifolia at a depth of 9m. I have attached photos of them.

The eggs from the upper three are from chromodorids, I guess. The eggs on the last picture may also be from a nudibranch, but I have no idea about family or species. Unfortunately I am not an expert concerning marine snails. Therefore I would kindly ask for your support to determine the different species.

I know it is quite difficult to do so (especially from these photographs only), but maybe you can tell me at least about the families. Thank you very much for your interest and effort.

Yours sincerely
Jeannine Dietz
Biologist at the Institute of Freshwater Ecolgy and Fisheries (IGB)
Biologist at the HYDRA-Institute of Marine Science (Elba Island, Italy)
Berlin, Germany

Dietz, J., 2003 (Dec 19) Eggs on Caulerpa taxifolia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jeannine,
Without local knowledge it is veru difficult to identify egg ribbons except in special circumstances. On intertidal shores around Sydney I can identify the egg masses of about 10 gastropods, because they have a distinctive shape and because I know from local knowledge that they are the only species around that lays that type of egg. Once you get into a geographic area where the fauna is more diverse, and we know relatively little about it, then the chances of correctly identify an egg mass get very small. At a guess the top two could be sacoglossan egg ribbons and the third could be a sacoglossan. The fourth doesn't look like an opisthobranch to me at all and is most likely that of a snail. For that matter they could all be snail egg masses. One way to distinguish opisthobranch eggs from other marine gastropods is to see where the eggs are in transparent capsules within the egg ribbon - either one egg per capsule, or in a few cases 2-3 eggs per capsule. If the capsules are linked to one another by a small string then you have the eggs of a Heterobranch gastropod [opisthobranch, pulmonate etc]. There eggs are always in capsules attached together like a string of beads. Unfortunately I can't see that detail in your photos.
Best wishes
Bill Rudman

Rudman, W.B., 2003 (Dec 19). Comment on Eggs on Caulerpa taxifolia by Jeannine Dietz. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Sea Slugs eating 'Killer Algae'

October 23, 2003
From: Emily

Is it true that a certain species of sea slug eats only "killer algae." And, is the US government conducting tests on this? I participate in high school debate, and this is a case a team is running. Are there any websites or books with the negative effects of these slugs?

Emily, 2003 (Oct 23) Sea Slugs eating 'Killer Algae'. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Emily,
By 'Killer Algae' I guess you are referring to Caulerpa taxifolia. There is a page on the Forum on that very plant. If you read the attached messages and go to the many suggested links you will find quite a discussion on whether slugs can control its spread.
Good luck with your debate
Bill Rudman

Rudman, W.B., 2003 (Oct 23). Comment on Sea Slugs eating 'Killer Algae' by Emily. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Do slugs eat Caulerpa taxifolia?

October 6, 2003
From: Ronnie

Are there any sea slugs that eat Caulerpa taxifolia? If so can you name the species, and if there are then why can't the sea slugs just eat it off the coast of California and Australia?

Ronnie, 2003 (Oct 6) Do slugs eat Caulerpa taxifolia?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Ronnie,
If you look at the Caulerpa taxifolia Fact Sheet and some of the other pages referred to there, you will see that some sacoglossan sea slugs do eat Caulerpa taxifolia. In fact we now have many records on the Forum of Caulerpa taxifolia being eaten by the slug Elysia tomentosa in many parts of the world. The problem is that in nature, most animals do not control the abundance of the food plants and animals they feed on. They may do so for a short period in a certain place but it's not a good evolutionary plan to eat out your food. What do you do when its all gone? Certainly with sacoglossan sea slugs, there is no evidence that any species can eat enough of the algae they feed on to greatly affect its abundance. That is one of the reasons we have to be very careful about introducing foreign animals into an area in an attempt to control a pest. Often the control animal does not control the pest and becomes a pest itself.
Best wishes
Bill Rudman

Rudman, W.B., 2003 (Oct 6). Comment on Do slugs eat Caulerpa taxifolia? by Ronnie. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Re: Caulerpa prolifera & biological control

March 28, 2003
From: Thierry Thibaut

Dear Cynthia and Bill,
Thank you very much for your support and comments on Caulerpa biocontrol. I'm very happy to hear that others labs are working on this subject, this mean that the idea was not stupid at all and I sincerely wish these labs much success because in France, our government refused for the second time in 3 years, to fund research on this biocontrol of the invasive Caulerpa even with the favourable recommendation of the scientific commission which has evaluated our project and even if more and more scientists ask to continue to study biocontrol (in any case these study were never funded by France). So actually research hre is very reduced.

Cynthia's comments on the media are important and highlight the fact that scientists have to communicate but to be very careful on what they are saying. Communication is essential.

Thibaut, T., 2003 (Mar 28) Re: Caulerpa prolifera & biological control. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Re: Caulerpa prolifera & biological control

March 21, 2003
From: Cynthia Trowbridge

Dear Bill and Thierry,
Thank you for your message, Thierry. Good to hear from you :-)

First, thank you for correcting me about the Caulerpa prolifera vs. racemosa ... I realized my error the minute I hit the send button on my message. I was about to send in a correction.
Second, Thierry, I admire your work very much. Indeed, I wish you would publish more as you are the leading person in the field with Caulerpa-feeding slugs.
Third, there are many labs working on the possibility of biological control with sacoglossans - I can think of at least 4 - so there is no need to personalize any comments.

Finally, you suggested that you consider that the Caulerpa-slug problem is different from other marine biological control cases in the public eye. Respectfully, I do not agree. As a resident of Oregon, one state away from where the field testing of insect-Spartina marine biological control is now happening, I can attest to the public feeling. In a state where crab harvest is a crucial part of our economy, I can attest to the public feeling about the proposed parasitic castrators that can change hosts from green crabs to native crabs.

Part of the issue of the Caulerpa-slug case is that too often the newspapers and other popular media state that the slugs are "the last hope" and "better than nothing". Most scientists would prefer to hear that feeding preference experiments have demonstrated that slugs are effective at reducing pest alga biomass, are highly specific, etc., etc. - thus indicating that it is a science-based management approach.

To quote a famous marine ecologist, "Ecology is no longer a spectator's sport": we need to get involved to solve problems. But, as scientists, we do need to ensure that the solutions are science-based. Thierry, I encourage you to keep publishing your science as your studies are essential to understanding the complex issue.

Thank you for considering my comments.

Trowbridge, C., 2003 (Mar 21) Re: Caulerpa prolifera & biological control. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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

Re: Caulerpa prolifera

March 14, 2003
From: Cynthia Trowbridge

Dear Bill and Rob,
Concerning Rob's message:
There are at least 3 invasive species of Caulerpa: C. taxifolia (aquarium strain), C. prolifera, and C. brachypus. For those of you unfamiliar with the last species, it is a NW Pacific species that recently appeared on Florida shores; it is overgrowing and killing the coral reefs.

All 3 species of Caulerpa are eaten by sacoglossan slugs and possibility of marine biological control keeps being suggested. I find it particularly disturbing that the suggestions for biological control are made extensively in the popular media (internet, newspapers, conference proceedings, books) but rarely in the scientific venue where peer review can put the issue in a more balanced light.

There are 2 major issues about biological control:
(1) does the potential consumer reduce the abundance or survival of the intended pest species?
(2) is the potential consumer highly specific?

Bill, you are entirely correct about the issue that sacoglossans rarely cause damage of host plants. I can think of only a few cases and they are primarily SPECIAL cases:
Placida dendritica controlling the distribution of the encrusting Codium setchellii on Oregon shores (Trowbridge 1992).
Placida dendritica causing extensive branch loss of the native Codium fragile on Oregon shores (Trowbridge 1993)
Placida cf. dendritica on New Zealand shores destroying the introduced C. fragile ssp. tomentosoides in high intertidal rockpools (Trowbridge 1996).
Placida cf. dendritica on Australian shores causing serious damage to the introduced C. fragile ssp. tomentosoides at Sisters in Port Phillip Bay, VIC (Trowbridge 1999, 2003/4).
Placida dendritica on Scottish shores causing serious damage to the introduced C. fragile ssp. tomentosoides at Oban, Argyll (Trowbridge 2002).

All of these studies demonstrate the potential role of sacoglossan herbivory. But in all of these cases, the slugs, at best, eliminate their host from a specific microhabitat (e.g., high pools or wave-protected shores). My recent JMBA note (2002) is the strongest case of herbivore control BUT I would emphasize that all of these cases are due to unusual circumstances. For example, Oregon shores have unusually high larval recruitment of invertebrates (due to oceanographic conditions) so large populations of sacoglossans develop. At Oban in Scotland, the currents between islands result in unusual hydrodynamic and larval settlement patterns. Thus, to extrapolate from these special cases to a general statement that sacoglossan herbivory will be important is presumptuous.

Now to the second point about the host-specificity paradigm (HSP). I would refer people to a recent invited review by Secord (2002). At the Marine Bioinvasions conference a few years ago, the proponents of marine biological control met and discussed the issues in a public forum. Secord was invited to review the issue. One of the 4 or so cases was the sacoglossan sea slug - Caulerpa proposal. Scientific consensus is that the proposal has too many unexplored risks.

A final brief word about risks, I have a paper accepted (pending minor revisions) about specialized sacoglossans that change their diets on ecological time-scales in Europe and Australia. Sacoglossans are specialized but their associations are dynamic. The view of static associations is not supported by field-based experimental data.

• Secord, D. (2002) Biological control of marine invasive species: cautionary tales and land-based lessons. Biological Invasions (in press).
• Secord, D. & Kareiva, P. (1996) Perils and pitfalls in the host specificity paradigm. BioScience, 46: 448-453.
• Trowbridge, C.D. 1992. Mesoherbivory: the ascoglossan sea slug Placida dendritica may contribute to the restricted distribution of its algal host. Mar. Ecol. Prog. Ser., 83: 207-220.
• Trowbridge, C.D. 1993. Interactions between an ascoglossan sea slug and its green algal host: branch loss and role of epiphytes. Mar. Ecol. Prog. Ser., 101: 263-272.
• Trowbridge, C.D. 1996. Introduced versus native subspecies of Codium fragile: How distinctive is the invasive ssp. tomentosoides? Mar. Biol., 126: 193-204.
• Trowbridge, C.D. 1999. An assessment of the potential spread and options for control of the introduced green macroalga Codium fragile ssp. tomentosoides on Australian shores. Consultancy report, CSIRO/Centre for Research on Introduced Marine Pests: Hobart. 43 pp.
• Trowbridge, C.D. 2002. Local elimination of Codium fragile ssp tomentosoides: indirect
evidence of sacoglossan herbivory? J. Mar. Biol. Assoc., U.K., 82(6): 1029-1030 .
• Trowbridge, C.D. in press. Emerging associations on marine rocky shores: specialist herbivores on introduced macroalgae. J. Anim. Ecol. (accepted pending minor revisions).

Thank you for considering my comments.

Trowbridge, C., 2003 (Mar 14) Re: Caulerpa prolifera. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Cynthia,
Bill Rudman

Caulerpa prolifera

March 13, 2003
From: Rob Brown

I am researching the invasive Mediterranean strain of Caulerpa taxifolia and the possible biological control of it using Elysia subornata, and have recently been curious about another Mediterranean Caulerpa. Caulerpa prolifera is not invasive in the Mediterranean, however its name surely implies that was invasive whenever/wherever it was first described. I know this is tangentially related to sea slugs, however I was hoping someone out there might know why C. prolifera is called prolifera.
Rob Brown

Brown, R., 2003 (Mar 13) Caulerpa prolifera. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Rob,
Your question is definitely very tangential to sea slugs but it does involve scientific names so I'll have a go. Basically you should try and see if the original description explains the origin of the name.
You have to be very careful in trying to interpret or 'translate' scientific names as they don't always mean what they seem. For example the nudibranch Noumea haliclona does not feed on the sponge Haliclona after which it was mistakenly named. Similarly, although prolifera sounds as though it may have something to so with being prolific I suspect it is based on the word proliferous which in botany refers to plants which freely reproduce vegetatively - by budding, sometimes from unusual places, such as shoots appearing from flowers.

Both prolific and proliferous come from a Latin word for offspring.

I am concerned to hear people are still seriously considering using non-native sacoglossans as biological control agents in the Mediterranean. I thought there had been considerable work done in recent years to show that the sacoglossan feeding behaviour probably increases the spread of C. taxifolia by causing bits to break off the plant and grow. Also there are plenty of examples worldwide now to show that, just as on land, introducing marine organisms to new oceans can cause massive ecological damage. Also, there is no evidence anywhere in the world to show that any sacoglossan species controls the population of its natural food algae, so why should we think they would do it if we shifted them to another ocean and put them on a new food plant?
Best wishes
Bill Rudman

Rudman, W.B., 2003 (Mar 13). Comment on Caulerpa prolifera by Rob Brown. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

References for some sacoglossans

February 25, 2003
From: Thierry Thibaut

Dear Bill,
In the course of my research on sacoglossans and Caulerpa taxifolia I have prepared what I think, are almost complete reference lists for the sacoglossans I have been working on. Here are lists for Lobiger serradifalci, Oxynoe olivacea, Elysia subornata and Oxynoe azuropunctata.
Thierry Thibaut

Thibaut, T., 2003 (Feb 25) References for some sacoglossans. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Thierry,
They are a very useful contribution
Best wishes,
Bill Rudman

Re: Caulerpa toxins

October 3, 2002
From: Kathe R. Jensen

Dear Mahdavi & Bill,
In regards to your request I have searched my reprint collection (I have to pack everything to send home very soon) and I have come up with the following references. Most of them are from before the Caulerpa taxifolia invasion, so they are not directly related to this species - and they are not all directly related to antibacterial or antimicrobial effects. However, they may give you some idea of the effects of the secondary metabolites in Caulerpa spp.

• Guerriero, A., Marchetti, F., D'Ambrosio, M., Senesi, S., Dini, F. & Pietra, F. 1993. New ecotoxicologically and biogenetically relevant terpenes of the tropical green seaweed Caulerpa taxifolia which is invading the Mediterrnanean. Helvetica Chimica Acta, 76: 855-864.
• Hodgson, L.M. 1984. Antimicrobial and antineoplastic activity in some South Florida seaweeds. Botanica Marina, 27: 387-190.
• Meyer, K.D. & Paul, V.J. 1992. Intraplant variation in secondary metabolite concentration in three species of Caulerpa (Chlorophyta: Caulerpales) and its effects on herbivorous fishes. Mar. Ecol. Progr. Ser., 82: 249-257.
• Paul, V.J. & Hay, M.E. 1986. Seaweed susceptibility to herbivory: chemical and morphological correlates. Mar. Ecol. Progr. Ser., 33: 255-264.
• Paul, V.J. & Fenical, W. 1986. Chemical defense in tropical green algae, order Caulerpales. Mar. Ecol. Progr. Ser., 34: 157-169.
• Vest, S.E., Dawes, C.J. & Romeo, J.T. 1983. Distribution of caulerpin and caulerpicin in eight species of the green alga Caulerpa (Caulerpales). Botanica Marina, 26: 313-316.

Best wishes,

Jensen, K.R., 2002 (Oct 3) Re: Caulerpa toxins. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Kathe,
Bill Rudman

Caulerpa toxins

September 30, 2002
From: Madhavi Agrawal

Hi ,
im a postgraduate student from the james cook univesity , Queensland , Australia

i am currently writing a literture review on the chemistry and chemical ecology of Caulerpales . concurrently , i am also looking at the levels of caulerpenyne and caulerpin in the australian species of caulerpa . i have been reading the book " killer algae " and it mentions on page 185, that studies have been carried out by several teams to see the affect of Caulerpa toxins on marine bacteria , and a dozen of other microorganisms . In addition , studies have been done on the break down products of the toxins. If anybody , has the references to articles dealing with these topics or anything to do with ecological effects of these toxins , could you please post them up on this website
Thankyou and best regards
Madhavi Agrawal

Madhavi Agrawal, 2002 (Sep 30) Caulerpa toxins. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Madhavi,
This is really outside the 'footprint' of the Sea Slug Forum, but there is a possibility that sacoglossan workers could have some information. If you have a look at earlier messages on this page, I have suggested a couple of relevant websites.
Best wishes,
Bill Rudman

Caulerpa taxifolia in Japan

March 28, 2002
From: Nishina Masayoshi

Dear Bill and Cynthia,
Concerning Cynthia's message. I heard recently that Caulerpa taxifolia was in Japan. This is may be true but I do not know where it is. It seems that the original tropical type of Caulerpa taxifolia is found in the southern parts of Japan like Okinawa and those are all small plants, 2-3cm
high. But I hear recently that there is also the form of C. taxifolia in Japan which destroyed a part of the Mediterranean. It may have escaped from an aquarium or the ballast of big ship.

Unfortunately there are no rules and regulations to prevent it coming to Japan. Anybody can import and buy it.
Best Regards,
Nishina Masayoshi

Masayoshi, N., 2002 (Mar 28) Caulerpa taxifolia in Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Caulerpa taxifolia in Japan... slug food?

March 27, 2002
From: Cynthia Trowbridge

Dear Bill and colleagues,
I attended the International Caulerpa taxifolia conference in San Diego in late January. Dr. Thierry Thibaut talked about his excellent work with Mediterranean and Caribbean sacoglossans. I talked, in part, about the NE Pacific sacoglossans that potentially may eat C. taxifolia on Californian shores (and Mexican shores if the alga spreads). The proceedings of the conference will be published in the Proceedings of the California Fish & Game, probably later this year.

An interesting but sobering fact we learned was that C. taxifolia ("killer algae") is now in Japan. With 19 spp. of Caulerpa and many varieties in Japan, it will be a large challenge to follow the probable spread of the alga on Japanese shores.

I would ask that if you do see the alga with ANY associated sacoglossans, please let me and the rest of the international community know. This is a very serious issue -- the aquarium strain of C. taxifolia (but not the "wild populations")is probably one of the worst marine invaders ever. With large numbers of species of Caulerpa -feeding sacoglossans, Japan may be less affected than other geographic regions; we can only hope.

Marine Ecologist & Invasion Biologist
Hatfield Marine Science Center
Newport, OR 97365 USA

Trowbridge, C., 2002 (Mar 27) Caulerpa taxifolia in Japan... slug food?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Caulerpa taxifolia - economical consequences

September 16, 2001
From: Hennes Zitzen

I'm a student from Holland and I'm writing a paper about Caulerpa taxifolia. I noticed that there is a lot of information about the species itself, but none about the economical consequences following this invasion, for example in fishery and tourism. Could you please make some comments about this subject, or direct me to a site where I can find some information.
Thank you very much,
Hennes Zitzen

Zitzen, H., 2001 (Sep 16) Caulerpa taxifolia - economical consequences. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Hennes,
Apart from the book, Killer Algae, the most useful source of information would be the website at:

It is very comprehensive with many links worldwide to other sites concerned with this algae.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Sep 16). Comment on Caulerpa taxifolia - economical consequences by Hennes Zitzen. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Re: Oxynoe and Caulerpa taxifolia

March 20, 2001
From: Cynthia Trowbridge

Dear Bill and French Students,

Hi. I have just returned from a brief visit to southern France and, thus, would recommend that the best person to discuss Oxynoe information for the region would be Thierry Thibaut. Thierry is working on the Oxynoe - Caulerpa issue in France and has been doing some very exciting experimental work for his PhD, much of which is currently in press.

Thierry Thibaut
Laboratoire Environnement Marin Littoral
Université de Nice Sophia-Antipolis
Faculté des Sciences, parc Valrose
06108 NICE cedex 02
Tel : 04 92 07 68 32
Fax : 04 92 07 68 49

Oregon State University

Trowbridge, C., 2001 (Mar 20) Re: Oxynoe and Caulerpa taxifolia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Cynthia,
I look forward to Thierry's work being published.
Bill Rudman

Oxynoe and Caulerpa taxifolia

March 16, 2001
From: French students

We are French students, in our college we work about Caulerpa taxifolia and we want to have informations about Oxynoe. Can you help us please.

French students, 2001 (Mar 16) Oxynoe and Caulerpa taxifolia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

I am not sure what information you want about Oxynoe. I have put your message on the Caulerpa taxifolia page so you will find some information above your message and also if you have a look below your message you will find othr messages which discuss sacoglossan sea slugs like Oxynoe and Caulerpa. If you click on any underlined word you will go to another relevant page.

To find even more on Oxynoe go to the SEARCH button and write oxynoe in the search box. It will give you a list of references to Oxynoe in the Forum.

I hope this is of some help. If you have a more specific question I would be happy to try and answer it for you.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Mar 16). Comment on Oxynoe and Caulerpa taxifolia by French students. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Re: Sacoglossans vs Caulerpa taxifolia

July 23, 2000
From: Kathe R. Jensen

Dear Bill,

Your query about the origin of the Cape Verde Ids and Canary Ids records raises a very difficult question. Obviously few sacoglossans have been collected at these localities till recent years. Also the fact that a number of Spanish malacologists have been working in the Caribbean and Central and South America in recent years may have made them more aware of amfi-Atlantic distributions. However, as even small pieces of Caulerpa are able to form new assimilators when given proper light and temperature conditions, it cannot be excluded that travelled (as egg masses or juveniles) on a torn off piece of Caulerpa. The fact that the Caribbean Elysia spp. with encapsulated or lecithotrophic development apparently have wider distributions than those with planktotrophic development is still a puzzle to me. I'd be glad to hear any other explanations.


Jensen, K.R., 2000 (Jul 23) Re: Sacoglossans vs Caulerpa taxifolia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


July 23, 2000
From: James Cobb

Dr Rudman,

Thanks for replying to my Killer Algae inquiry and for alerting me that related messages from others were in the offing.



Cobb, J., 2000 (Jul 23) Thanks. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jim,
I'm glad my prediction that your question would bring forth further comments proved true. As Cynthia says in her latest message, it would be good to get further views and ideas as well.
Bill Rudman.

Re: Sacoglossans vs Caulerpa taxifolia

July 22, 2000
From: Cynthia Trowbridge

Dear Bill and Kathe,

The spread of the invasive green alga Caulerpa taxifolia is only one of many species of macroalgae, accidentally introduced to distant shores. Many invaders are potentials hosts to ascoglossan (=sacoglossan) slugs. Notable examples include two species of Caulerpa, three subspecies of Codium fragile, many species of the red alga Polysiphonia, many species of Chaetomorpha and Cladophora, etc., etc.

The suggested introduction of slugs from Florida to the Mediterranean is only one recent suggestion of biological control that has been made. Other suggestions have been made at conferences and in research in press and in prep. by various ecologists. Thus, my comments about considerations of biological control were designed to be *general* considerations for introduced macroalgae and potential biological control, not specific to Caulerpa taxifolia per se.

In some cases, the potential consumers (putative control agents) have functional chloroplasts; in other cases, the potential consumers do not. I made no statements about specific species of slugs; I apologize to Kathe and any others who assumed that I was making specific comments. I personally work on a different suite of introduced macroalgae (Codium fragile and Polysiphonia spp.).

It would be interesting to hear others' views. Thank you for considering my comments.


Cynthia Trowbridge

Hatfield Marine Science Center
Oregon State University

Trowbridge, C., 2000 (Jul 22) Re: Sacoglossans vs Caulerpa taxifolia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Re: Sacoglossans vs Caulerpa taxifolia

July 21, 2000
From: Kathe R. Jensen

Dear Bill,

Thanks for opening the page on this important issue. Unfortunately bureaucracy may not be enough to prevent the "introduction" of Caribbean sacoglossans to the Mediterranean. Spanish researchers have now collected Elysia subornata (as E. cauze) from the Canary Islands as well as the Cape Verde Islands, so I'm afraid it is only a question of time before Nature starts its own large-scale experiment.

I am not sure I quite understand Cynthia's point about functional or non-functional kleptoplastids. Elysia subornata has functional kleptoplasts, but Oxynoe spp. do not. Oxynoe azuropunctata may be a stronger competitor than O. olivacea, the local Mediterranean species, and this is one of the things I have told the French group of scientists MUST be tested carefully. As all shelled sacoglossans are restricted in diet to Caulerpa spp. (and I have actually tried - in vain - to give them only non-Caulerpa algae for several weeks), I do not fear that O. azuropunctata will switch to other algae (though obviously it will be able to switch to the native C. prolifera). Elysia subornata, on the other hand might be able to switch to feed on Halimeda or Udotea (which have the same cell wall structure as Caulerpa), but it is highly unlikely that they will switch to non-Caulerpales algae. This is another thing I have asked the French group to investigate. What I fear more is that once it has entered the Mediterranean, the road to the Red Sea and the Indian Ocean is wide open, and then we may have a serious problem.

• Ortea, J., Moro, L., Bacallado, J.J. & Espinosa, J. (1998) Catalogo abreviado de las especies del orden Sacoglossa (= Ascoglossa, Mollusca: Opisthobranchia) de las Islas Canarias y de Cabo Verde. Revista Academia Canaria de la Ciencias, 10(4): 85-96.
• Ortea, J., Moro, L. & Espinosa, J. (1997) Nuevos datos sobre el genero Elysia Risso, 1818 (Opisthobranchia: Saccoglossa) en el Atlantico. Revista Academia Canaria de la Ciencias, 9(2-4): 141-155.
• Jensen, K.R. (1997) Evolution of the Sacoglossa (Mollusca, Opisthobranchia) and the ecological associations with their food plants. Evolutionary Ecology, 11: 301-335.

Best wishes,

Jensen, K.R., 2000 (Jul 21) Re: Sacoglossans vs Caulerpa taxifolia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Kathe,
Are you suggesting that the presence of Elysia subornata at Cape Verde Ids and Canary Ids is a recent introduction or a previously unnoticed natural distribution?
Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Jul 21). Comment on Re: Sacoglossans vs Caulerpa taxifolia by Kathe R. Jensen. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Re: Sacoglossans vs Caulerpa taxifolia

July 18, 2000
From: Dr. Cynthia Trowbridge

Dear Bill,

In case your readers do not know, Caulerpa taxifolia has now appeared in San Diego, Calif. (USA) so the invasive algal spread continues.

I would like to make two comments.

1. The introduction of species for biological control makes the implicit assumption that the control species (in this case, the slugs) will not change diet. Yet, the stenophagous ascoglossans (= sacoglossans) can change their diets on ecological and evolutionary time scales. The change of diet of the N. Atlantic Elysia viridis from Cladophora spp. and Codium tomentosum to Codium fragile ssp. tomentosoides and C. fragile ssp. atlanticum this century exemplified the former point. In terms of evolutionary change, there have been 2 major species radiation events in the Order Ascoglossa (=Sacoglossa) associated with change in algal foods. Thus, even marine specialist herbivores have the potential to change their diets.

2. If we were to introduce slugs for biological control (an action that I STRONGLY oppose), I personally feel that we need to evaluate whether species with functional kleptoplasty would be effective at reducing algal populations. So far, all the examples of which I am aware are species that retain non-functional chloroplasts (e.g., Placida dendritica on the Oregon coast, USA and Placida cf. dendritica in Australia). [NOTE: Functional kleptoplasty = removing and keeping algal plastids alive and functioning in your own body]

I would be interested in hearing the views of others on this extremely interesting topic.



Hatfield Marine Science Center
Oregon State University

Trowbridge, C., 2000 (Jul 18) Re: Sacoglossans vs Caulerpa taxifolia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Sacoglossans vs Caulerpa taxifolia

July 17, 2000
From: James Cobb


In Chapter 5 of Alexandre Meinesz' book, Killer Algae, work is described which indicates sacoglossans might be suitable as a biological control in the Mediterranean of the invasive algae Caulerpa taxifolia; but as of date of publication, bureaucratic delays had prevented large-scale tests of this hypothesis.

Please bring me up to date as regards use of biological controls against C. taxifolia.



Cobb, J., 2000 (Jul 17) Sacoglossans vs Caulerpa taxifolia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jim,
There has been passing comment on this topic on the Forum, and I have heard colleagues from Europe discussing it at meetings. Sacoglossan opisthobranchs are well-known feeders on species of Caulerpa, so when an introduced species of Caulerpa invades an area, it is understandable that sacoglossans are thought of when control methods are discussed.

I have added a copy of a review of Killer Algae [from the University of Chicago Press website] to the Forum because it contains some useful background information on the subject, plus information on obtaining a copy if anyone is interested.

There are many websites discussing the problem of C. taxifolia in the Mediterranean. One of these gives a valuable (in English) summary of the whole topic, including possible plans of action to control its spread. One very worrying paragraph says:

"With the European Union funds, researchers are now mapping the plant's journey and testing ways to destroy it. In a laboratory in Nice, France, biologists have bred thousands of snails, a species brought from the Caribbean, where it devours the local variety of the seaweed. The team is waiting for permission from the French goverment to unleash the snail army. But critics fear that the remedy may introduce new bio-troubles. Meinesz, an advocate of the operation, insists it is safe. "We have proof that the snail only attacks this seaweed," he said, adding confidently, "We'll put it in the sea in the spring and it will die from cold in winter ...." In Paris, the Ministry of Environment is not yet convinced."

I live in Australia which now suffers from the disasters of failed attempts at biological control. In many cases the so-called 'controller' ignores the pest it is introduced to control, and finds a much more tasty native species to destroy.

In this case, two Mediterranean sacoglossan species, Oxynoe olivacea and Lobiger serradifalci have had no appreciable effect on the introduced Caulerpa so there is a proposal to release two Caribbean species Elysia subornata and Oxynoe azuropunctata in the belief that they will do a better job. To my knowledge there is no evidence to show they would.

The author of Killer Algae, Meinesz, states he has proof that the Caribbean species would die off over the Mediterranean winter and so would be controllable. Again I know of no published evidence for this assertion.

I know Kathe Jensen, an expert on sacoglossan biology, is opposed to this proposal, and until there is real evidence that these introduced sacoglossans would not affect the local fauna, and would control the introduced Caulerpa, I would consider it rash and irresponsible to proceed with their introduction.

I am not quite sure what you mean by 'large scale tests of this hypothesis' but if you mean field experiments, then I hope it is not just bureaucracy that is delaying them. Once these animals are released in to the field we can no longer control them - and we certainly cannot remove them if they prove a disaster. Biological control methods should only proceed after many years of rigorous testing. Australia has certainly learnt that lesson and today before organisms are introduced to control introduced pests, years of research is conducted, both in the country of origin of the proposed control organism, and in Australia. Any other approach will almost certainly lead to a 'cure' which is worse than the disease.

As a passing comment, have a look at the Caulerpa on which I photographed Oxynoe viridis. This Caulerpa was introduced to the Sydney region about 30 years ago, and has thrived in certain areas. Although not its natural food, Oxynoe viridis is often found on it, but it makes no appreciable dent on the Caulerpa population. When we look at species of sacoglossan anywhere in the world, does anyone have evidence to show they greatly effect algal populations any where?

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Jul 17). Comment on Sacoglossans vs Caulerpa taxifolia by James Cobb. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from