Green is the new sexy, Part I

I was making my last run through the wet lab today, about to head off to forage for lunch before a meeting elsewhere, when I saw this in one of my bowls:

This is one of my feeding treatments for the juvenile urchins. The sheet of green stuff is Ulva sp., a green alga several species of which grow locally in the intertidal. You also see it in harbors and estuaries. This particular bit was growing ferally in one of the large outdoor tanks in an area of the marine lab called the tank farm.

You can see that the algal body (called a thallus) has a fairly distinct edge, except for the parts that the urchins have munched through. Can you also see the cloudy pale green water that runs sort of horizontally across the middle third of the bowl? That’s the stuff that caught my eye. After glancing at the clock I figured I had just enough time to take a quick peek under the scope, and if I really didn’t care about eating lunch I could even snap a few pictures and still make it to my meeting on time. Anyone who knows me personally understands that I organize my life around food and the next time I get to eat. The fact that I was willing to forego lunch to look at this green spooge should tell you how exciting this was.

(It turns out that a few minutes later the person I was supposed to meet with e-mailed me and asked to postpone our meeting until next week. Yes! This means actual quality time with the microscope and the spooge.)

Here’s what a spawning green alga looks like:

That undulating column on the left side is a stream of reproductive cells being released by the thallus. And yes, those are my little urchins chowing down. They like eating Ulva much better than the coralline rocks they’d been subsisting on until recently.

Under the compound scope at 400X magnification, the reproductive cells look like this:

The tiny little cells zooming around are about 2.5 µm long. The way they swim suggests that they have flagella. Do they look familiar?

They should. They look a lot your typical flagellated animal sperms! I don’t think it’s a coincidence that my first thought upon seeing the green stuff in the bowl was “Spooge!”

But here’s where it gets tricky. For algae, looking and acting like sperm doesn’t mean that something is sperm. More on that in the next post.