Who has had lettuce nudibranchs?

[Diomedes]

Nudibranchs are also "sea slugs" or Opisthobranchs, they are just a different order of sea slugs than an order called Sacoglossa which your typical Elysia "lettuce nudibranch" belongs to...
But I highly doubt these Sacoglossans will eat your red tuft algae -
(Wrangelia argus perhaps?) because sea slugs are notoriously narrow minded food wise, often specifically matched for one and only one prey/resource.

I don't know about tropical ones, but most local sea slugs live 1-2 years according to my studies (2 years ago)...

If you love Sea Slug Pics, a neat site to check out is the "Nudi of the week" - http://slugsite.us/bow/nudiwkps/nudiwk24.html

Stephen