Here's a view of the hydroid under a microscope. Remember that although they look a bit like flowers, hydroids are animals related to sea anemones and have stinging cells for capturing prey that swim by.
While I was looking at the hydroid, I noticed small eggs capsules attached to it (next photo). Note that each white blob inside the capsule is a tiny developing snail.
I looked around for a snail that might be responsible for these capsules. Eventually I found this small purplish snail (see below), but I'm somewhat frustrated (and intrigued) that I'm not sure what species it is, or whether it might be related to the egg capsules noted above. Because I'd like to find out what it is, I'm posting a few photos of this mystery snail.
Below, you can see that it looks like the snail has an operculum (trap door) that might be calcareous.
Next I noticed some larger egg capsules attached to the kelp. They were swirled and sparkling!
I looked around again, suspecting these might be nudibranch (sea slug) egg capsules. After some searching, I finally spotted a nudibranch (next image). I don't know what species this is yet, but I'll be asking for help and will update this post if I find out.
Below are a few views of these attractive egg capsules. The shininess is due to the shells of the developing larvae inside the capsules. [Yes, nudibranchs have shells that they eventually lose after the larval stage!]
Amazing to explore the small world on a blade of kelp!
ADDENDUM (11 October 2012): Jeff Goddard has assisted with the identification of this nudibranch and the egg ribbons. The nudibranch above is a juvenile Dendronotus venustus (formerly Dendronotus frondosus), and the egg ribbons were also produced by Dendronotus venustus.