You may have heard that earlier this month the California Department of Fish and Wildlife postponed the scheduled opening of the commercial Dungeness crab season. Gasps of dismay were heard all over the state from Californians whose Thanksgiving traditions include cracked crab, as well as from the folks who make a living fishing for them. The closure is due to the detection of domoic acid (DA) in the crabs. DA is a naturally occurring toxin produced by some species of diatoms in the genus Pseudo-nitzschia. DA is ingested by filter-feeding animals such as mussels, and due to the process of bioaccumulation occurs in higher concentrations in the tissues of animals that feed at higher trophic levels. Humans can be affected by DA also, which is why state officials warn people not to collect and eat mussels when DA levels are high enough to be concerning.
Since the crab fishery closure I’ve been wanting to do my own informal assessment of Pseudo-nitzschia in the water, but with one thing and another I didn’t have the time or opportunity until today. This morning I collected a plankton sample and gave myself a few hours to play with it before I had to start grading papers. Pseudo-nitzschia was present but not incredibly abundant, especially compared to what I saw this past August. Today’s Pseudos were in chains of 3-4 cells, instead of the 12 cells that were common in the summer.
But it turns out that Pseudo-nitzschia wasn’t the most interesting thing I found in the plankton today. Just about at the time that I was supposed to stop playing and start grading, I saw one of these:
This was a big cell, measuring 250 µm long and 80 µm wide. Right away it had a diatom look about it: the visible protoplasm was golden-brown, the color of diatoms; it didn’t have any cilia or flagella; and it was scooting along very slowly, the way a pennate diatom does. But it wasn’t anything that I recognized, which made it all the more intriguing. I made an executive decision to investigate further, even if it meant not getting my papers graded. Damn the consequences, science was calling!
I did some poking around, searching through photo databases of local diatom species, not having much success. Since this was a new (to me, at least) critter, it warranted not just a photo and video but an entry in my real lab notebook:
Besides, spending time with a microscope, notebook, and pencil feels more like doing science than when I take pictures. And it has been a while since I’ve been entirely stumped, so I was having fun.
It turns out that this diatom isn’t all that uncommon in Monterey Bay. I happened across a report of a diatom named Tropidoneis antarctica that had been detected in a plankton tow off our very own Santa Cruz Wharf about a week ago. BINGO! I had a name for my mystery critter, learned something new, and got to play for a morning. And notice that I spelled the genus name wrong in my notebook? Oops.
And, by the way, the papers did all get graded. I am (un)fortunately far too responsible to have let them not get graded. I’m working on that, though. Give me another 50 years or so and I’ll be as flaky and unreliable as the next guy.