Chemical ecology


Two Glossodoris pallida and their food sponge, Cacospongia sp. Vanuatu. 1995. PHOTO: J.K. Stenhouse

Without a protective shell, sea slugs have had develop other defences against predation. These include cryptic colouration or camouflage and behavioural modifications such as only being active at night. Another major development has been the use of chemicals to make them posionous or at least extremely distasteful to potential predators. Opisthobranchs have become a target for research by marine products chemists and gradually we are discovering just the widespread and complex ways chemicals are used by sea slugs. Many store these chemicals in special glands in their skin. What is starting to fascinate chemists and physiologists is the many different ways the molecules are produced. In some cases the chemical molecules [often called metabolites] are removed from their food and stored unchanged by the opisthobranch. In other cases the molecules from the food are modified by the opisthobranch, and in some cases the opisthobranch makes new molecules itself. Usually, each species of opisthobranch has very specialised food requirements and often its defensive molecules are uniquely different from closely related species.

See below for relevant messages.
See Defensive Glands Page for further references and messages.

The above photo illustrates a good example of the role chemicals play in the life of these animals. The two nudibranchs are the chromodorid Glossodoris pallida on a large colony of a grey-black sponge which is almost certainly their food, the dictyoceratid sponge Cacospongia sp. A study by Avila & Paul (1997) on this species shows that, like other chromodorids, G. pallida is storing antifeedant chemicals, which are derived from its food, in particular parts of its body. They also showed that these chemicals do indeed deter fish.

In particular they found sponge-derived terpenoid compounds concentrated around the mantle border and in the mucous secretions of the mantle. They found that at their natural concentrations these chemicals deterred some crabs and reef fishes from feeding. They also found that animals which had had their mantle borders removed were much more likely to be eaten than those in which the mantle was intact. This is a very significant advance in our understanding of the biology of these fascinating animals.

• Avila, C. (1995): Natural products of opisthobranch molluscs: a biological review. Oceanography and Marine Biology: an Annual Review, 33: 487-559
• Avila, C. & Paul, V.J. (1997) Chemical ecology of the nudibranch Glossodoris pallida: is the location of diet-derived metabolites important for defense?. Marine Ecology Progress Series, 150: 171-180.
• Cimino, G., Fontana, A. & Gavagnin, M. (1999) Marine Opisthobranch Molluscs: Chemistry and Ecology in Sacoglossans and Dorids. Current Organic Chemistry, 3(4): 327-372.
• Faulkner, D.J., Ghiselin, M.T. (1983) Chemical defence and evolutionary ecology of dorid nudibranchs and some other opisthobranch gastropods. Mar. Ecol. Prog. Ser. 13: 295-301.
• Karuso, P. (1987) Chemical ecology of the nudibranchs, pp. 31-60. In: Scheuer, P.J. (Ed.), Bioorganic marine chemistry, vol. 1: vii + 185 pp. Springer-Verlag, Berlin.

Authorship details
Rudman, W.B., 2004 (July 27) Chemical ecology. [In] Sea Slug Forum. Australian Museum, Sydney. Available from

Related messages

Re: Diterpenes - what are they?

July 27, 2002
From: Edwin Cruz-Rivera

Although a little late, here's a reference that may help clarify the role of terpenes and how they relate to slugs and other consumers:

• Paul, V.J., Cruz-Rivera, E. and R.W. Thacker. 2001. Chemical mediation of macroalgal-herbivore interactions: ecological and evolutionary perspectives. In: Marine Chemical Ecology, J. McClintock and W. Baker (eds.), CRC Press, Boca Raton, pp.227-265.


Cruz-Rivera, E., 2002 (Jul 27) Re: Diterpenes - what are they?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Edwin,
Additions, comments, etc are never too late
Bill Rudman

Diterpenes - what are they?

July 3, 2002
From: Virginie Fruh

Can anyone let me know what role terpenes or diterpenes have in an opisthobranch's ecology? Are they aromatic compounds which allow opisthobranchs to communicate? Or are they pigments?
Virginie Früh

Fruh, V., 2002 (Jul 3) Diterpenes - what are they?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Virginie,
Terpenes and diterpenes belong to a group of molecules produced by many plants and animals. The noxious nature of these molecules makes them important antifeedant agents. Many opisthobranchs remove these molecules from their food and incorporate them into their own defence system, either through glandular secretions or by concentrating them into vulnerable parts of their body. 'Recycled' molecules like this are known as Secondary metabolites and they form an important role in many opisthobranch defence strategies. An excellent review is Avila (1995). Also have a look at the following pages for further information and links:
Soft Corals - Chemical Defence
Defence mechanisms
Chemical Ecology

• Avila, C. (1995) Natural Products of Opisthobranch molluscs: a Biological Review. Oceanography and Marine Biology, Annual Review, 33: 487-559.

Bill Rudman

Rudman, W.B., 2002 (Jul 3). Comment on Diterpenes - what are they? by Virginie Fruh. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Medical uses

May 31, 2002
From: Alexander Taborda Marin

I am interested to know about the medical use of opisthobranchs, and about the biotecnology and natural products chemistry. Thanks for your collaboration.

Marin, A.T., 2002 (May 31) Medical uses. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Alexander,
There is a growing literature on the natural products chemistry of opisthobranchs. Have a look at the Fact Sheet on this topic and other messages on this page for some clues on finding answers to your questions.
Best wishes,
Bill Rudman

Chemical information about Sea Slugs

March 15, 2001
From: Arnaud Parenty

Hi Bill,
Here is the abstract of an article issued last year that discuss about chemistry and ecology of opistobranch. It may be of interest to your visitors

Guido Cimino, Angelo Fontana & Margherita Gavagnin. 1999. Marine Opisthobranch Molluscs: Chemistry and Ecology in Sacoglossans and Dorids. Current Organic Chemistry, 3(4): 327-372.

"Opisthobranchs are marine molluscs apparently unprotected by physical constraints of a shell which is either reduced or completely absent in the adults. Their survival is based on a series of defensive strategies, which involve cryptic behaviour and use of deterrents. During the last twenty years, many studies have been performed to characterize the chemicals isolable from these animals. In this paper we summarize the studies covering two large groups of opistobranch molluscs: sacoglossans and dorids. The main aim is to give to the readers a brief view of the compounds isolated from these molluscs, and, when it is possible, to suggest an ecological role for them. The Order Sacoglossa has been selected as it contains a wide range of morphological types from primitive species with a relatively strong external shell to shell-less types. The chemical studies of these molluscs have been reviewed with the aim of constructing a general scenario based on chemical evidence. Similar reasons prompted us to review the chemical data of the shell-less dorid nudibranchs belonging to the superfamilies Eudoridoidea and Bathydoridoidea. In this case, the review dates from the literature subsequent to Karuso's 1987 review "Chemical Ecology of Nudibranchs". The selection of the two groups, sacoglossans and dorids, is also due to their different, but exclusive feeding habits, green algae for sacoglossans and sponges for dorids. The critical analysis of all these studies illuminates the extraordinary capability of opisthobranch molluscs to create new chemistry through either bio-accumulation of selected metabolites from their dietary sources, bio-transformation of dietary compounds, or de novo bio-synthesis of useful chemicals. However, it is difficult to determine the boundaries of these investigations. In fact, their ecological contributions are relevant and applications useful for man are foreseable."

It's quite long. Sorry :)
Best regards
Arnaud Parenty

Parenty, A., 2001 (Mar 15) Chemical information about Sea Slugs. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Arnaud,
Guido Cimino has been a leading light in the study of the chemical ecology of opisthobranchs for many years.
Best wishes,
Bill Rudman

Medical uses

May 18, 1998
From: Jacob Hall

Dear Sir:
I am a student in Louisville, Kentucky in the United States. I am asking you cordially to help me. I am wondering what two medical purposes nudibranchs have towards humans. Please, your urgent assistance would really be appreciated.
Thank you,
Jacob Hall,
9th grade student

P.S. Please send soon!!

Hall, J., 1998 (May 18) Medical uses. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

I don't know offhand any direct medical uses that nudibranchs could be put to. If anyone does, could they let us know.... Bill Rudman