Onchidoris bilamellata - California swarming (2)

December 13, 2001
From: Clinton Bauder

Hi Bill,
To accompany my other message here are some pictures of swarming Onchidoris bilamellata in Carmel laying eggs. One thing to note is the large number of small barnacles in the bottom of the lower picture [also see inset in upper photo]. I believe these are Balanus crenatus. We've had an incredible bloom of these barnacles lately. They literally covered everthing; bryozoans, hydrocorals even kelp. I'm guessing the current explosion of this barnacle-eating nudibranch is a natural response to the barnacle bloom.



Bauder, C., 2001 (Dec 13) Onchidoris bilamellata - California swarming (2). [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5827

Dear Clinton,
Celeste's question about 'conga lines' of slugs certainly has opened our eyes to a very interesting phenomenon from California to Scotland and Ireland. While high population numbers certainly suggest an abundance of food, why they should swarm, and trail, is a puzzle. Another question which arises is whether this swarming is a common phenomenon. Although there have been no published reports of this phenomenon since Pelseneer (1922), that does not necessarily mean that they haven't been busily swarming on a regular basis. Certainly something else to keep an eye out for in the future.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Dec 13). Comment on Onchidoris bilamellata - California swarming (2) by Clinton Bauder. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5827

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