Sea Slugs changing colour

December 3, 1999
From: Diana Huynh

I am doing an experiment on sea slugs/hares and I was wondering if you can send me any information on my topic. My experiment is about if they will change their color to the color of the algae that we feed them and I need to know some types of algae that are different colors and if they are available to get in the San Diego area. I have approximately 2 weeks to do my experiment. Please if you can help me.

Diana Huynh

Huynh, D., 1999 (Dec 3) Sea Slugs changing colour. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Diana,
I'm afraid from the other side of the Pacific I'm not the best person to ask about sea life in San Diego. Perhaps you should try your local museum or university.

I can make a few general points. Firstly even if you knew exactly what you were going to do I very much doubt you could do it in 2 weeks. Finding out what animals do usually takes a very long time, often with much failure on the way.

Have a look at the page on Colour, where some different ways sea slugs can change colour is described, and also look at the page on Solar-powered sea slugs where colour changes which are caused by the colour of the algae in the sea slugs is described.

Some Sea Hares change colour as they grow and change their algal food, but this is a relatively slow process. The most likely animals you could use to show how they change colour are sacoglossans, which often keep algal plastids and their pigments, in their bodies. One species we know changes colour as it changes algal food is Elysia cf. furvacauda but that is only found in southeastern Australia, and only eats certain species of algae.

Apart from not knowing which slug to choose, your other main problem will be finding out which algae the slug you choose will eat. Most are very choosy about their food.

I'm afraid this is not much help other than to demonstrate to you that finding out what animals do is a very difficult and time-consuming task, usually with lots of problems. Although you can sometimes make a flower change colour by putting different coloured water in the vase, its a little bit more difficult to demonstrate such things in living animals.

Best wishes,
Bill Rudman.

Rudman, W.B., 1999 (Dec 3). Comment on Sea Slugs changing colour by Diana Huynh. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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