Aggregation of Stylocheilus in the Philippines

July 21, 2008
From: Marcel Tanke


Dear Bill,

On the Anilao sandy bottom dive site near Malnit (site is also called Secret Bay), we saw 4 or 5 mass aggregations of these nudibranchs. The aggregations were no more than 2 meters from each other and consisted of about 100 (?) individuals each. I checked if there was any food below one aggregation. Just a slight 'waving' of the hand (or a kick of the fin) easily disperses the whole group. I did not see anything special below them. Just sand / pebbles. Although, in the whole area the sand is covered with some algae. The movement of the nudibranchs was relatively fast, crawling over- and on top of each other.

Locality: Anilao, 3 meter, Philippines, 12 July 2008, Sandy bottom. Length: 3 cm. Photographer: Marcel Tanke.

I have not been able to ID this nudibranch. Would you know it?
Any suggestion for this behaviour?

Best regards,
Marcel

marceltanke@cs.com

Tanke, M.A., 2008 (Jul 21) Aggregation of Stylocheilus in the Philippines. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21722

Dear Marcel,

The animals are the small Sea Hare Stylocheilus striatus. If you go to the species Fact Sheet you will find quite a few messages recording these swarming events in many parts of the world. Also have a look at the Mass Mortality Fact Sheet for more discussion on this phenomenon in Stylocheilus and other Sea Hares.

Best wishes,
Bill Rudman

Rudman, W.B., 2008 (Jul 21). Comment on Aggregation of Stylocheilus in the Philippines by Marcel Tanke. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21722

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