Re: Aggregation of Stylocheilus striatus in Indonesia [1]

January 23, 2006
From: Paul Whitehead


Concerning message #15378 on aggregation of Stylocheilus:

Dear Bill,
As promised attached are some photos of the other two aggregation species, which all aggregated with the same week and on the same site (Retal Larry, Lembeh Straits) following the September full moon.

Locality: Retak larry. Lembeh Straits, Indonesia. Depth: 3 meters. 15 September 2005. black sand beach with sparse cover. Photographer: Paul Whitehead

Immediately after the Stylocheilus aggregation the "white" species [see message #15630 ] aggregated over the site covering an area of about 20 meters by 20 meters and avaeraging about 10 animals per square meter. Whilst this aggregation was occurring, this third species aggregated covering the same area with about 10 animals per square meter again.

The whole cycle of the three aggregations lasted 1 week.

Paul

pw@whiteheadimages.com

Whitehead, Paul, 2006 (Jan 23) Re: Aggregation of Stylocheilus striatus in Indonesia [1]. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/15629

Dear Paul,
This is Philinopsis cyanea, another species with a reputation for irregularly occurring in large aggregations. I recall seeing two such aggregations, one in Zanzibar in 1971, and another in mainland Tanzania a few years later - but they don't seem to be a regular occurrence - or perhaps there are too few people looking out for them. Aggregations like this are a good opportunity to see the range of colour variation in a species. I see that in your photo alongside there is a small specimen of the  'white swarmer' Gymnodoris ceylonica.

Philinopsis cyanea is another eater of opisthobranchs, usually cephalaspidean  bubble shells, but it also feeds on Stylocheilus [see Mike Roberts message #14082]. As with Gymnodoris, I suspect the timing of the Philinopsis aggregation with the Stylocheilus aggregation is a coincidence rather than a consequence. That is not to say that the Philinopsis would not have taken advantage of so much food around.
Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Jan 23). Comment on Re: Aggregation of Stylocheilus striatus in Indonesia [1] by Paul Whitehead. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/15629

Factsheet

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