Rafting

At Doran Beach late this afternoon, I went to pull a tangle of seaweed off a larger piece of drift kelp so that I could confirm the identity of the kelp.  In the process of doing so I couldn't help smiling when I revealed this little sea star holding onto the kelp.  It's interesting to see them in situations like this, because you can then imagine how they could "raft" around, using kelp or other seaweeds to disperse to different sites along the coast.

 

The kelp is Pterygophora californica, sometimes known as Walking Kelp.

The sea star is a bit more challenging.  Here's a close-up:

 

It looks like a species of Pisaster to me, with five fairly stubby arms.   There are 3 species of Pisaster in this area.  The habitat — rafting on kelp — probably isn't that useful as a clue to the species identification because I'm guessing all three Pisaster species could end up in that circumstance.

This individual was very small, ~5 mm across.  And it looks very similar to juvenile Ochre Sea Stars (Pisaster ochraceus) that we're familiar with in the rocky intertidal zone on the outer coast (see photo here).  But when I thought about it, I realized that I wasn't completely sure how easy it would be to tell the three species of Pisaster apart at that size.  They're very easy to separate as adults, but I don't know when they start to differentiate.  Does anyone?  It would be fun to know!  At what size do Short-spined Sea Stars turn pink?  When do Giant Sea Stars develop blue rings?

Here are links to Ochre Sea Star (Pisaster ochraceus), Short-spined Sea Star (Pisaster brevispinus), and Giant Sea Star (Pisaster giganteus) adults.