Armina californica Last Supper?

October 5, 2005
From: Jan Kocian

Hello Bill,
Last year, on October 2nd, I dove at Sunnyside Beach near Tacoma, [Washington, USA] and came across a forest of Sea Pens (Ptilosarcus gurneyi) and among them many Armina californica  feeding on them. I had problems with my strobe firing so I did not get much of documentation. This Saturday, October 1st, I returned to the site and eagerly retraced last year dive. I did find plenty of Armina californica but very few Sea Pens. I went twenty feet deeper then last year and still, the only pens I came across were devoid of polyps. And nudibranch busy of finishing whatever was left. There were egg clusters on the sand, many of the slugs had just their rhinophores "eyes" sticking out of sand, some in pairs.

Locality: Sunnyside Beach, near Tacoma, Washington, USA. Puget Sound, NE Pacific. Depth: 85 feet. Length: 55 mm. 01 October 2005. sand. Photographer: Jan Kocian

I wonder if the Armina could eat themselves out of existence?

Kocian J., 2005 (Oct 5) Armina californica Last Supper?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jan,
Thanks for these interesting observations. Did you find the sea pen out of the mud like this? Concerning your question about whether the Armina could eat themselves out of existence? This is always a possibility for animals with very specialised diets. When food is short, they can be in direct competition with others of the same species. This has led to many of them have very quick lifecycles. By growing to maturity quickly - and eating voraciously - they get more than their fair share of the available food supply and so are more likely to produce the next generation than are slower growing and slower feeding Armina. The other strategy they have is producing planktonic veliger larvae, which are able to move away from 'home' where the food has been eaten out, and find another supply of sea pens somewhere else.

Your finding of many egg masses shows that the present generation have done their job, and even if they die from starvation, their genes have a chance of carying on the species.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Oct 5). Comment on Armina californica Last Supper? by Jan Kocian. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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