A few days ago I told my friend Brenna that I'd hunt around in the marine lab for a bit of a green alga that she wants to press. I had a pretty good idea of where to look, only the animals I'd seen it on had been removed from the exhibit hall. I asked for and got permission to examine the animals behind the scenes. And fortunately I had remembered correctly, and I was able to pick off some nice clumps of dark green stuff.
Bryopsis corticulans is a filamentous green alga. It grows to about 10 cm in length and is a dark olive color. When emersed it sometimes looks almost black. I've seen it in the intertidal in a few places, where at low tide it resembles nothing so much as a shapeless slime. It's very difficult to see the beauty of organisms when they're out of their natural element, which in this case is water.
But see how pretty it is when submerged?
One of the reasons I love the algae is their very inscrutability. I enjoy discovering the beauty of organisms that, at first glance, don't look like much. Many of the filamentous algae, both the greens and the reds, have a delicate structure that requires close examination to be appreciated. Fortunately, I have access to microscopes, so close examination is very easy.
The thallus of B. corticulans is relatively simple, consisting of a bipectinate arrangement of filaments.
Here's a closer view:
This is a shot of the main axis and side filaments. The small green blobs are chloroplasts. One thing to notice is that there are no crosswalls separating any of the filaments. That's because the thallus is coenocytic, essentially one large cell with a continuous cytoplasm. Coenocytic cells are common in fungi, the red and green filamentous algae, and a few animals. In animals, coenocytic cells are often referred to as syncytial. They can arise in one of two ways: (1) adjacent cells fuse together; or (2) nuclear replication occurs as usual during normal mitosis but cytokinesis (division of the cytoplasm) does not. However the syncytium arises, it can result in very large cells. Even though B. corticulans itself is a small organism, some algae in the Bryopsidales consist of single cells that can be over 1 meter long!
Sometimes things that appear simple at first glance conceal a deeper complexity when you look more closely.
At the marine lab we have many seawater tanks and tables in various shapes sizes. For my purposes the most useful are the tables. The tables are shallow, about 20 cm deep, but what's nice about them is that water depth can be managed by varying the height of the stand pipe in the drain. I have some critters wandering free within tables and others confined to tanks, colanders, or small screened containers. One of my tables contains the paddle apparatus that stirs jars of babies when I'm raising larvae.
All of these tables are gravity fed from a supply of semi-filtered seawater supply in the ceiling of the building. The seawater flows through some sand filters before being pumped to the top of the building, but is by no means entirely clean. We get all kinds of things recruiting to the surfaces of tables, jars, or anything that sits in a seawater table for more than a few days. Some of the stuff that recruits is a nuisance, such as the spirorbid worms that build tiny calcareous spiral tubes on just about anything and scrape up the knuckles something awful. Other stuff is benign, and more or less ignored until it gets in someone's way. Or until I decide to take a close look at it.
Last year I finally decided to look at some of the red filamentous stuff growing on the bottom and sides of one of the tables. To the naked eye it doesn't look like much, which is why I love having access to a good compound scope. Here's my notebook page from that day:
Today I took some pictures of the same stuff. It's really pretty and delicate when you see it magnified!
I am always gratified when I look back at drawings I made in the past, and find that they still hold true and can be corroborated by photographs. The filamentous reds are so pretty! This is not the best time of year to find sexy algae, and I saw no reproductive structures on any of the filaments I examined. Maybe next spring.
In a different table (the table where the paddle apparatus is, actually) there is some brownish fluffy stuff growing on the bottom surface. I took a look at some of it and noticed right away that the threads didn't have their own inherent structure the way the Antithamnion defectum does. These threads seemed to be sticky, and when I picked up a little piece of the fluff it collapsed into a blob. I had to tease apart the threads in a drop of seawater to make sense of what was going on.
These diatoms are really cool! I have no idea which species they are, though. We do have local diatom genera (Thalasionema and Thalassiothrix) in which adjacent cells stick together at their ends to form this kind of wonky chain, but the cells themselves look different. So for now these are unidentified diatoms.
There's no doubt that they are diatoms, though. They have the typical diatom color, a golden-brown that I would name Diatom if I got to name colors, and I could see through the microscope that the cells are enclosed in a silica structure called a frustule.
This is the diatom color:
At higher magnification the sculpting on the frustule surfaces becomes visible. Unfortunately, at higher magnification you necessarily have less depth of field, so it's more difficult to take photos that show this kind of detail.
Some of these cells appear to be doubled. I think one of two things is going here: either the cells simply remain attached to each other by a thin layer of mucilage, or a cell has recently divided and the two cells that are stuck together are the resulting daughter cells. Throughout the growing season diatoms reproduce clonally (each cell divides to produce two genetically identical daughter cells), and their populations can expand very rapidly in response to either natural or artificial nutrient inputs. Because the cells are enclosed by a rigid frustule, however, this clonal replication cannot continue indefinitely. Perhaps diatom reproduction is fodder for another blog post, if people are interested.
This week it has been very windy on the coast. As in hope-the-next-gust-doesn't-arrive-while-I-am-still-holding-onto-the-door windy. Seriously, the other day I almost wrenched my shoulder when the wind caught a door I was walking through just as I opened it. I should have braced myself before opening that door. The wind also blows around dust and pollen, exacerbating everybody's spring allergies.
Despite all that, the wind is a good thing because it is the driving force behind coastal upwelling, the oceanographic phenomenon that brings cold, nutrient-rich water from depth to the surface. Upwelled water provides the nutrients that primary producers such as phytoplankton require for photosynthesis. The simple equation is: Sunlight + nutrients = photosynthesis. With the days getting longer as we head toward the summer solstice, this is the perfect time of year to be a phytoplankter. (Note: a phyto- or zooplankter is any creature that lives as plankton)
It takes several days of sustained winds from the north to start upwelling along the coast. I record the temperature in one of my seawater tables every day and keep an eye out for decreases that might indicate upwelling. Given that it's been crazy windy since Sunday (today is Wednesday) I thought today would be a good day to collect a plankton sample and see what's going on.
What did I find? Lots of phytoplankton, right on schedule!
Most of these critters are diatoms, of which there were several different types. Diatoms are unicellular algae whose cells are encased in a fancy silica shell called a frustule. More on that later. In Monterey Bay, the first phytoplankters to bloom in the spring are usually diatoms; they can take advantage of upwelled nutrients to fuel rapid asexual division so their populations grow quickly. Photosynthetic creatures from diatoms to redwood trees can perform the biochemical magic of capturing light energy and converting it to chemical energy held in molecules containing fixed carbon (e.g., glucose). Diatom blooms provide food for grazing zooplankters such as copepods and krill. These small animals become food for any number of larger animals, and so on up the food chain, so in every sense possible the phytoplankton are the foundation upon which the entire marine food web is based. Interested in saving the whales? Then you should focus your energies on saving the phytoplankton. Seriously.
The largest object in the photo above is a large protozoan ciliate called a tintinnid. They also live in glass shells, only theirs is called a lorica (L: "body armor"). The tintinnids I see most frequently in tows from the Wharf have a clear goblet-shaped lorica that is entirely transparent. These tintinnids are big, for single-celled creatures, up to over 1 mm in length. That's a lot bigger than some multicellular animals!
Tintinnids are frantic little swimmers. They are heavily ciliated, which means they can swim really fast. The one in the photo was tangled up in the phytoplankton and squashed under a cover slip, which conveniently retarded its motion, but in this video you can see its little cilia beating. I added a few seconds of a different tintinnid swimming solo to the end of the video clip, which will give you a better idea of how they swim.
Here are some other plankters from today's sample:
Photo #1 - Diatoms. The large cell with the spines on both ends is Ditylum brightwellii, one of my favorite scientific names. Chaetoceros cells each have long spines at the corners of the cells. The spines link adjacent cells together, forming chains.
Photo #2 - Chaetoceros. At least two species of diatoms in the species Chaetoceros.
Photo #3 - Chaetoceros debilis(?). This species forms spiral chains.
Photo #4 - Assorted phytoplankton. In this photo the five roundish cells are the dinoflagellate Protoperidinium. They have two flagella, one in a groove that wraps around the cell and one that trails free. The two button-like cells near the center of the picture are (I think) the diatom Thalassiosira. There are two chains of Chaetoceros debilis and several other chain diatoms. That big opaque vaguely bullet-shaped object to the right of center? That's a fecal pellet, probably from a copepod.
Speaking of copepods, as usual they were very abundant, both as adults and as larvae. In terms of numbers of individuals, copepods are likely the most abundant animals in the sea. Copepods are small crustaceans that feed on phytoplankton and are in turn eaten by many larger animals. In life they have beautifully transparent bodies, allowing us to see the beating heart. See for yourself:
And, finally, about those diatom frustules. As I mentioned above, a diatom's frustule is a sculpted shell made of silica (SiO2). It comes in two parts, an epitheca and a hypotheca, that fit together like the two halves of a petri dish. In fact, I use a petri dish as a frustule model for my marine biology students; it is made of roughly the same substance and demonstrates the size relationship between the epitheca and hypotheca.
The large round centric diatoms best show the structure of the frustule. Here's the best photo I was able to take today of one of the very large centrics, Coscinodiscus:
I hope that later in the season I can take some better photos of these diatoms. They are so beautiful that I really to do them justice. So much diversity early in the season makes me hope for a good productive season. We'll see!
but what you really needed to be certain of the ID was the rest of the photo:
Huzzah again for natural history! I love it when natural history provides the answer to a taxonomic or identification question. Sometimes you need to see the organism where it lives in order to understand what it's all about. Quite a lot of modern biology has to do with grinding up organisms and examining their DNA; while I do appreciate the evolutionary and ecological insights these data provide, it's really not my cup of tea. I'd rather spend my time looking at intact organisms than their molecules, and getting outdoors to see them in nature instead of running gels and staring at computer algorithms. As in most other walks of life, it takes many kinds of work to get at the whole picture in ecology, and I am grateful to be able to contribute a little piece to the puzzle.
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.
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!
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.