Coral-feeding Berthellina

February 3, 2004
From: Steven Garcia

I hope your doing great. Last night I happened to take a look at my reef tank through a video camera with a night scope. I noticed that something large, as big as my thumb, was on my button coral.

I turned on the lights, and it was a yellow nudibranch. I think. Can you tell me by the picture if this is a coral eating slug and what kind it is? It looks as though it did damage to the button. I just lost a bubble coral recently, and I never lose my corals. Should I be worried?

Thanks for your help!
Steven O. Garcia

Garcia, S., 2004 (Feb 3) Coral-feeding Berthellina. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Steve,
It would be helpful to have some clues as to where your yellow slug might have come from. Even without knowing that, I am pretty sure your yellow animal is a species of Berthellina and probably Berthellina citrina. It is a sea slug, but not a nudibranch. It belongs to a group called the Notaspidea, or side-gilled slugs, because they have their gill on the right side of the body,usually hidden in the space on the right side of the body between the upper mantle and the foot.

I'm afraid the news is not good for your bubble coral - nor I suspect for the Berthellina when you read this. Species of Berthellina have often been reported to feed on sponges but Bertsch & Johnson (1981) reported that in Hawaii they also eat various corals. Have a look at Scott Johnson's earlier message. I don't think they have been observed eating 'Bubble corals' but I am afraid there is no reason why they shouldn't find them tasty. I guess you will not be that pleased to have advanced our knowledge of feeding in this species but hopefully you will be in time to save your coral.

It would be useful to clarify what your 'Bubble Coral' is, as your observation is quite interesting. Would you know if it is Plerogyra sinuosa, which is a species from the tropical Indian and Pacific Oceans?

• Bertsch, H., & S. Johnson. 1981. Hawaiian nudibranchs, a guide for SCUBA divers, snorkelers, tidepoolers, and aquarists. 112 pp. Oriental Publishing Co., Hawaii

Best wishes,
Bill Rudman

Rudman, W.B., 2004 (Feb 3). Comment on Coral-feeding Berthellina by Steven Garcia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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