Category: Marine biology

If you visit the California rocky intertidal in the spring or summer, one of the first things you notice will be the macroalgae, or seaweeds. They are incredibly abundant and diverse this time of year, covering just about every bit of rock. In fact, in a landscape sense the only visible organisms are macroalgae and surfgrass:

Of the three major divisions of algae (the greens, browns, and reds), the red algae are the most diverse. We have several hundred species along the California coast, and while they don’t get as big as the kelps (which are brown algae) they display an astonishing assortment of morphologies, colors, and life history complexities. Almost all of the algae in the photo above are reds. The olive-greenish stuff? Yep, those are reds; multiple genera of reds, in fact. The dark brown things? Those are also reds, again representing more than one genus.

Within the incredible diversity of red algae, today I want to focus on two species: Microcladia coulteri and Plocamium pacificum. Both of these algae have delicate branching forms that make beautiful pressings. But despite their apparently similar morphologies, they represent different taxonomic orders and have completely different lifestyles. Let’s take a look at how similar they actually are:

Pretty tough to distinguish, aren’t they? The specimen on the left is a bit more robust in comparison, but if you had only one of these in front of you and nothing to compare it to you’d probably be hard-pressed to determine which species it is.

This is where an understanding of natural history becomes invaluable. Since these species are morphologically so similar to each other, an extremely helpful piece of information is where (and how) each one lives. In terms of habitat, these species can be found pretty much right next to each other, so that doesn’t help much. However, the surface on which each species grows tells you exactly what you need to know.

The specimen on the left in the photo above is Plocamium pacificum, a member of the taxonomic order Plocamiales. It lives from the mid-low intertidal to the shallow subtidal and is always attached to rocks, as you can see below:

The specimen on the left was taken from a thallus that was growing on a rock. This means that it is Plocamium pacificum. Now we can label our photograph with one name.

The specimen on the right was growing as an epiphyte (“on plant”) on a large blade of another red alga. This epiphytic lifestyle tells me that it is not Plocamium, but a species in the genus Microcladia in the taxonomic order Ceramiales. When I brought it into the lab to key it out I was able to identify it as Microcladia coulteri. Three cheers for natural history!

Here’s a picture of M. coulteri growing on blades of another red alga, Mazzaella sp. See how green the Mazzaella looks? Color isn’t the only factor that determines which major group an alga belongs to, and can in fact be quite deceiving!

Finally, we have both specimens identified:

Which is all well and good when you have two specimens in hand that you can compare directly to each other. But what if all you have is this little bit?

Would you say this is Plocamium, or Microcladia? What would you base your decision on? And how certain would you be?

Submit answers (with justifications!) in the Comments, and I’ll give you the answer tomorrow.

Today I decided to look at some scuzz growing in one of the seawater tables at the marine lab. This table is populated mostly by coralline rocks, although I have some pet chitons running around in it.

I picked out a promising rock and examined it under some decent light. Most of the rocks have at least some fuzzy red filamentous algae growing on them; this one also had a bit of a filamentous green, which made it a promising subject for photography. I already knew what the green was (Bryopsis corticulans) but didn’t recognize the filamentous red. The Bryopsis is in the lower right corner of the rock in the photo below:

What was noticeable about the Bryopsis and the mystery red is the difference in size. Bryopsis looks positively dainty until you compare it with the red. Wanting to take a closer look at the red, I plucked off a bit and mounted it on a microscope slide. This is really the only way to see what’s going on with these filamentous algae, and it works like a charm. You don’t have to make a cross-section or anything; you just put the piece in a drop of water, add a cover slip, and look at what you can get:

What first caught my eye was the rather simple branching pattern. The central axis is made up of roughly rectangular cells, each of which has two side branches that are opposite each other. Each of the side branches has branchlets on only the upper surface. Branching like this is relatively easy to draw (things spiralling around in three dimensions are really difficult for me), although my drawing isn’t nearly as pretty as the real thing.

This microscope view, along with my little sketches, provided me with enough information to key out this alga even though it didn’t have any reproductive structures. According to the dichotomous keys in Marine Algae of California* (the book that marine biologists refer to as the MAC, our Bible for identifying the algae) it is Antithamnion defectum. The MAC says that this species is common on other algae and can be found both intertidally and subtidally from southern British Columbia to Baja California. It could very well be that I see this species in the field, but these filamentous reds look pretty much the same, at least to my inexpert eye. It really does take a microscope to figure out what I’m looking at.

*Abbott, Isabella A. and George J. Hollenberg. Marine Algae of California. Stanford: Stanford University Press, 1976. Print.

Part of what makes the marine algae so fascinating to me is their life cycles. I’m intrigued by organisms that do things differently from us. And to be honest, from the perspective of someone who studies invertebrates and their life cycles, we humans are rather boring: we’re born into in one body, reproduce (maybe), and then die, all in the same body. Ulva, on the other hand, follows the typical plant example and has a life cycle that includes alternation of generations.

Without going into too much detail, let’s just say that Ulva has two generations within a single life cycle, one called a sporophyte and the other called a gametophyte. The difference between the sporophyte and gametophyte is the number of chromosome sets found in the cells of the respective generations: sporophytes have two sets of chromosomes per cell, a condition which we describe as being diploid (2n), while gametophytes are haploid (1n) and have only one set of chromosomes per cell. The diagram below lays it out nicely. Note that the gametophyte in the diagram is white, while the sporophyte is green.

The little white circles in the diagram above are the reproductive cells. These cells are produced by either the gametophyte (in the case of gametes) or the sporophyte (in the case of spores).

Now, determining if what you’re looking at is a sporophyte or gametophyte can be easy or difficult, depending on whether your species is isomorphic (‘same form’) or heteromorphic (‘other’ or ‘different form’). Unfortunately for us, Ulva happens to be isomorphic, which means that the sporophyte and gametophyte are for the most part morphologically indistinguishable. However, if you knew what kind of reproductive cells a particular generation produces, you could deduce whether that generation is a sporophyte or a gametophyte, right? So, is there any way to determine whether a 2.5 µm cell is a spore or a gamete?

Yes, there is! In the group of algae that includes Ulva the spores are quadriflagellate, which is just a fancy way of saying that each one bears four flagella. The gametes are biflagellate, having (you guessed it) two flagella. Now it’s just a matter of counting flagella on these tiny reproductive cells released by the specimen of Ulva in my bowl.

And voilà!

It’s clear that these cells have only two flagella, right? This means that they are gametes, not spores, and the thallus that produced them was the gametophyte!

Pretty dang nifty, isn’t it?

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.