Sacoglossans vs Caulerpa taxifolia

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.