This is what I found washed up on the beach:
If you need something for scale, here's a picture with my field notebook. (My notebook is about 4 5/8" x 7".)
I realize this might be difficult because some of the characters used to identify algae are better experienced in-the-hand, e.g., color subtleties, texture, and flexibility.
Perhaps you can see that this seaweed is leaning towards golden brown? It's not always true, but in this case I thought the color probably was a clue pointing towards a member of the brown algae (i.e., not a green or a red algae).
From the scale, you can tell that this blade is fairly large. So I started to wonder about a kelp. The problem was, it didn't look like any of the local kelps I am familiar with.
(Note also that this blade was reproductive — the dark brown patches on the left end are reproductive structures, not shadows.)
Here's another angle:
After a little more time, I realized something was throwing me off — the narrow "branches" at the bottom of the blade. At first I didn't give these too much thought and I passed over them as a possible stipe, i.e., where the blade connects to a holdfast (the attachment to the substrate).
But there were things about this blade that were familiar — the color and texture — and those reproductive patches. And then it hit me — what if those little branches at the bottom weren't part of a stipe at all? What if they connected the blade to something else, like a float (also called a pneumatocyst)?
You can see a hint of what I mean in this picture from Big Sur:
Is it possible that Bull Kelp (Nereocystis luetkeana) blades grow to be as wide as the blade I found today? I hadn't seen them this size before. As mentioned, my field notebook is 4 5/8" (11.7 cm) wide. I measured the blade, and at its widest it was 16 cm across.
I went to the Marine Algae of California and started reading. Sure enough, Bull Kelp blades are reported to at least 15 cm wide. So the size of the blade I found today is at the extreme end of the range, but possible for a large Bull Kelp blade.
And is it possible that Bull Kelp is reproductive this early in the year? Generally, I think of Bull Kelp being very early in its annual growth cycle during the spring (see next photo of very young Bull Kelp from 24 March 2015).
The Marine Algae of California reports that Bull Kelp's reproductive season is from early May through December. Well, if my identification is correct, I can now add early April to that description!
But I still have questions. Although this large, reproductive Bull Kelp blade washed up on Bodega Head on 12 April 2015 — did it grow locally, or did it start growing somewhere else, break free, drift, and then wash ashore here far from its origin?
And what conditions cause Bull Kelp blades to grow so wide? Have you seen them this wide before, and if so, are there certain conditions under which you expect to find wider blades?