Re: What does Placida dendritica eat?

November 6, 2002
From: Cynthia Trowbridge

Dear Yi Zhang and colleagues,
I would like to add to Bill's comments and ask for additional observations from Scandinavia. Here are my observations (mostly published reports) by region.

British Isles: Placida dendritica from British Isles (type location is in Southern England) eats:
Codium tomentosum (native alga)
Codium fragile tomentosoides (introduced)
C. fragile atlanticum (introduced)
Bryopsis plumosa (presumably native)

I assume that the slug may eat C. vermilara (native alga) as well. I have been working on a population of C. vermilara at Guernsey, Channel Islands this Sept. So far, I have found tons of Elysia viridis but no Placida [my visit was too late in the season]. Have any colleagues seen the slug on C. vermilara? If so, I would be keen to hear the details.

Has anyone from Norway or Sweden seen P. dendritica on C. fragile scandinavicum (introduced)? If so, it would be great to have this recorded.

Sagami Bay, Japan: Placida cf. dendritica from Sagami Bay, Japan (= Baba's Placida sp. = Marcus's Placida babai) eats:
Codium fragile (native)
C. arabicum (= C. adhaerens)
plus 3 other native Codium spp.
plus several Bryopsis spp.

Okinawa: "Placida dendritica" from Okinawa which may be Ercolania/Stiliger (according to Kathe's message in summer) eats:
Codium intricatum (confirmed)
Bryopsis harveyana (tentative)
also reported by 3 different malacologists on Caulerpa (no feeding observations)

Yoshi Hirano, Yayoi Hirano, and I have done feeding preference experiments with this sacoglossan species in July 2002.

Oregon: Placida dendritica from Oregon eats:
Codium fragile (native)
C. fragile tomentosoides (introduced)
Bryopsis corticulans

SE Australia and New Zealand: Placida cf. dendritica from SE Australia and New Zealand eats:
Codium fragile novae-zelandiae (native)
C. fragile tasmanicum (native)
C. fragile tomentosoides (introduced)
C. convolutum (= C. adhaerens)
many other Codium spp.
many Bryopsis spp.

Other reports include:
Derbesia spp.
Halimeda sp.
Cladophora sp.

Some of these reports are in a manuscript currently pending publication; others are already published. Please contact me directly if you wish additional details.

Trowbridge, C., 2002 (Nov 6) Re: What does Placida dendritica eat?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Cynthia,
It is good to get a summary of their food preferences. There is also Jui-Sheng Chang's animal from Taiwan which is reported to feed on Codium edule. What with the difficulty of identifying the slugs, and I guess the difficulty in identifying the algae, I am amazed that you have persevered with your study of these little animals. I am sure a lesser ecologist would have retreated years ago.
Bill Rudman


Placida dendritica

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