Nudi behaviour question

December 13, 2002
From: Ken Howard

Hi Bill,
I was attracted to the behavior of this nudibranch in the Solomon Is. last month. The JPEGS are in sequence. In photos 1 and 2 [lower left], it was arching its body out over this gap in the coral. It then crawled down the coral head it was on and proceeded to cross over [other photos] on what looks to me like a mucus 'bridge'. My question — do you know if the nudibranch could have excreted the 'bridge' itself, or did it just sense it was there already? There are a fair amount of sand particles, etc. on the 'bridge' so I think it had been around for a while — just wanted to try and find out if the nudi could have created it previously, or was just making use of what another critter manufactured.

Thanks in advance for your help!
Best wishes for the Holidays,

Howard, K. , 2002 (Dec 13) Nudi behaviour question. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Ken,
The stretching out over a gap behaviour you describe in the lower left photos is typical behaviour of many nudibranchs. It's obviously a searching behaviour, looking for somewhere else [more interesting?] to go. The mucus bridge you describe, which we can see in some of the other photos, is almost certainly produced by the coral colony. The coral looks to be a species of Porites. Many corals, including Porites, clean themselves when covered in silt or sandy particles by producing large quantities of mucus, which form a sticky layer over the colony. This layer sloughs off with the unwanted particles attached. If there is water movement the mucus layer drifts off. As the mucus continues to be produced for some time you get this phenomenon of the coral colony producing a streaming mucus layer which could indeed form the 'bridge' you describe. So my guess is the nudibranch, Chromodoris lochi, is just using a temporary bridge formed from this streaming mucus to get across the gap between the two coral colonies.
Bill Rudman

Rudman, W.B., 2002 (Dec 13). Comment on Nudi behaviour question by Ken Howard . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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