Jim Sullivan 03/02/16 Phytoplankton Form and Function in the Turbulent Ocean


Thanks, Dennis. And thank you all for coming out to the late show. This is where we work the blue material. So like Dennis said, today I'm going to talk to you about phytoplankton and some of the amazing adaptations they have to exist and thrive in our oceans. For those of you who were here about a month ago, a colleague of mine also from URI – Jan Rines – gave a talk on the dazzling diversity of marine life and microscopic life in the ocean. This is really a follow onto that talk, except for I'm going to look at one specific group of organisms – the phytoplankton in the ocean. I'm going to try to give you a quick 45-minute course in phytoplankton ecology. So what are phytoplankton? It's Greek for a drifting or wandering plant. And they are microscopic plants, and we commonly call them algae. A lot of people also call them protists because they have characteristics of both animals and plants as you're going to see. They kind of skirt the world in between the two things.

It's hard to categorize a lot of them. In almost everything I'm going to talk about today, all these organisms are single cells – a complete organism. They don't have a brain. They don't have a nervous system. They're complete single cell organisms, but they're not simple organisms. For those of you who know SpongeBob SquarePants, this character is called Plankton. He's drawn after a diatom – a phytoplankton in the ocean. And he's one of the more complex characters in this cartoon. He wants to control the world and just take over the world. And I think he's a good analog. These are not simple organisms. And SpongeBob was created by a marine biologist, and I think he did it on purpose. So we'll start off with, what is the difference between a phytoplankton or a plant cell and an animal cell? We're animals. Phytoplankton generally are considered plants. There are a lot of things we share in common with plants. We're all organisms of some type that came from the same thing eventually. We have mitochondria just like plants do.

Mitochondria are like the powerhouse of the cell. We both have a nucleus. Our nucleus is where the DNA or the genetic material of organism is stored. And there's a whole bunch of what we call organelles, and these are specialized membrane-bound functional areas where specific things are done to keep the cell going. Both cells have cytoplasm or the goop that is inside of a cell. The thing that makes plants somewhat different is that they have chloroplasts, and chloroplasts, for those of you that don't know, are little organelles that allow a plant to conduct photosynthesis. Plant cells also have a very large cell vacuole. This is like an empty space in the cell. Animal cells have cell vacuoles too but they're usually much smaller and not as important. And a big difference is, plant cells have a cell wall.

Animal cells have a cell membrane and so do plant cells, but a lot of plant cells have a thick cell wall made of various material. While I'll say this is a general phytoplankton cell, a lot of phytoplankton are also bacteria. So the difference between a bacteria and a eukaryotic cell, which has a nucleus, is that it has no membrane-bound organelles. It doesn't have a nucleus. It doesn't have any of these other things. Everything just kind of floats around inside of it. But there are a lot of phytoplankton that are large bacteria in the ocean. Here are two simple slides of a phytoplankton cell and an animal cell. On the left here, you see the phytoplankton cell. You can see it definitely has cell structure. That's because of its cell wall. It's all brown. This is all the pigments from the chloroplasts that are in it. This is where the nucleus is. And on the right hand side is an animal cell. You can see it's kind of an amorphous little blob. There's its nucleus. No pigment.

This animal cell is actually from us. If you were to swab your cheek and take the liquid that comes off and put it on a microscope slide, this is what you see. It's a cheek cell, a human cheek cell. Both of these cells are about the same size. They're 50 microns, roughly, in size. For reference, 50 microns is slightly less than the diameter of your hair. So these are truly microscopic organisms. They're very small. You can barely see them with your eyes, if at all. The size range of phytoplankton can go anywhere from ten times smaller than 50 to ten times larger. So they can go anywhere from five microns – even a little bit smaller – all the way up to 500 microns, which you can easily see with your eye. Just to reiterate, phytoplankton cells are a single cell and it's a complete organism. For us, it takes roughly 37 trillion cells to create a human.

And you'll see that they can do many of the things we can do with just one. So why are phytoplankton important? Who knows what this formula represents? It should be the most famous formula in the world, more than Einstein's e=mc2. Who knows what this is? Photosynthesis. I heard someone say it. So this is the photosynthetic equation where you take carbon dioxide and water, and in the presence of sunlight and chloroplasts – so plants that can conduct photosynthesis – you produce glucose and oxygen. Both of these products of photosynthesis are really important and I'll take both of them separately. The first is oxygen. This is a hard number to put an exact value on, but somewhere between 50 and 80 percent of earth's oxygen is produced by phytoplankton. If you like to breathe, you should really appreciate phytoplankton. You've got to look at – this is a shot of the earth. They call it the big blue marble for a reason. There is a lot more water from land.

This is the Pacific Ocean and you can barely see any land in here, and it's filled with phytoplankton. So you can appreciate the scale of where this number comes from. This is also important too, for those of you who don't know what glucose is. It's sugar. This is one of my favorite sugars. So this is what we do as animals. We do respiration. We eat sugars or other things. We breathe oxygen and then we exhale carbon dioxide and water vapor. This whole thing feeds back what we exhale – the plants use and it's a nice round, recyclable reaction. That production – that food – the donuts that these phytoplankton create – again, it's a hard number to put a value on, but we know pretty sure that greater than 50 percent of the earth's primary production is produced by phytoplankton. So phytoplankton are the base of the world's food chain.

So in this cartoon, for people who know SpongeBob SquarePants and Plankton, he wanted to take over the world. Phytoplankton do rule the world. Them and bacteria – without them, we would not be here. For those of you who aren't biologists or don't get the concept of a food chain, this is a really, really simple one. We have phytoplankton growing in sunlight, doing their primary production. They are eaten by zooplankton which are like shrimp-like, crab-like crustaceans that live in the ocean. They're eaten by small fish which are in turn eaten by larger fish and larger fish until we get to the largest apex predators, and whales and big things like that. I have this big arrow pointing to humans here. We take food out of every part of this food chain. We harvest shrimp, and crabs, and other zooplankton. We obviously eat a lot of small fish like anchovies and things like that.

We eat mackerel. We definitely eat mahi-mahi and other large fish. And we eat sharks and harvest whales, unfortunately, for a long time. We actually also harvest phytoplankton, too. Phytoplankton are used as a food supplement. So we need this entire food chain and it is critically important to our survival. In the ocean, there is amazing algal diversity. And what I mean by that is it's estimated there are one to two million species of unique phytoplankton out there. This is something that has puzzled phytoplankton ecologists for a really long time. It's, why? And this was first posed – or one of the better posing of this question – by Hutchinson in 1961 in a paper called The Paradox of the Plankton. He asked the question, "How is it possible for a number of species to coexist in a relatively isotropic – which means uniform – or unstructured environment, all competing for the same sort of things?" And what he is trying to ask in an easier way is, "Why are there so many species in this simple environment?" When you look out at the ocean – in a horizontal sense when you look over it, it seems like this vast, unchanging, uniform environment.

It looks like a desert. And when you look at a desert, you say, "I don't see one or two million kinds of plants there. There's just a few that have learned how to survive and that's it." So it's, why do we have so many species? And the reason is, yes, in a horizontal sense the ocean does seem like a desert. But the vertical ocean has another dimension. It changes very rapidly and it changes rapidly in a lot of ways. This simple graph shows depth going down – so this is going deeper in the water column – versus the amount of different parameters we can measure in the ocean. Light decreases exponentially. A lot of light at the surface. You go down deep enough, there's no light at all. There's a whole bunch of other things that a lot of things need to exist in the ocean. There's nutrients, the temperature, or the density of the water, CO2, PH. All these vary in some way with depth. Sometimes they're lower at the surface and higher at depth.

Sometimes they're higher at surface and lower at depth. The point is that this complex vertical structure – and this can change. The ocean can change in a foot. It can actually change in just a couple inches – radically change. This complex structure creates what we call niche space. It creates unique environments that certain organisms learn how to exploit. This is where we get that amazing species diversity from. There's a lot of different phytoplankton groups in the ocean. The early ecologists looked at them and one of the easiest ways to categorize them was by color, so that's what we have now when we group them into these larger groups. We have the blue-green algae, and this is this group I was talking about. These are called the cyanobacteria. They truly are bacteria.

They grow in a lot of places. I'll talk about some of the problems they create a little bit later. There's the red and green algae, and the golden-brown algae. I don't have time to talk about them all. That would be a whole course in phytoplankton ecology. I'm going to specifically look at two of the major groups that are in the ocean. These are probably the most important when you're dealing with phytoplankton ecology – the diatoms and the dinoflagellates. If you look at this photo – this is pure cultures of all these different groups – you can see the amazing color they have. This is due to the different pigments they have and how they absorb light. This is a pure culture of diatoms. This is a pure culture of dinoflagellates.

And you can see they belong kind of in the golden-brown algae. So if we're going to compare and contrast diatoms and dinoflagellates, we'll start here. These are some SEM – scanning electron microscope – micrographs of some single cells of each of these groups. You can see here the diatoms are very symmetrical. They look like pillboxes. However, the dinoflagellates are not very symmetrical and they have a lot of odd shapes. They have horns, and spines, and various appendages. The diatoms are made out of silica glass. This cell wall, which I talked about that these plants have, is actually made of quartz. While the dinoflagellates, for the most part, most of them their cell wall is cellulose. It's tree bark, essentially. So if you look at living pictures – those are SEM's. Those are dead cells, basically the hollow remnant of their cell wall.

These are some live shots of diatoms and dinoflagellates. I'll go through and compare what makes these two groups different. Diatoms are generally considered nonmotile. They don't swim. Dinoflagellates can actively swim. You'll see a great example of this in a minute. I put this in quotes that they're nonmotile because diatoms actually can move. They can change the buoyancy of their self. So like a helium balloon floats in the atmosphere, a diatom can become lighter and float in the water. It can also become heavier and sink. They can control how they go up and down. So while they can't actively swim, they can move in the ocean. Diatoms are generally considered colonial. That means you have a lot of single cells that live together in a colony. So each one of these is an individual cell of a diatom. These are all individual cells. This is hundreds of individual cells in a big, blob-like colony. Dinoflagellates are normally solitary. They live as single cells.

While it's not always true – this is a colony or a chain of dinoflagellates and these occur as single cells. For the most part diatoms are colonial organisms – they live as a group – and dinoflagellates live as solitary organisms. As far as their growth, diatoms are really fast growers. They can divide – create a copy of themselves – in usually one day, sometimes less. Dinoflagellates, comparatively much slower grower. On average, they divide every two to three days they'll create a copy of themselves. My colleague up at URI, Dr. Ted Smeda, came up with two great words to describe how these things exist in the ocean. He calls diatoms "perennial plants" and dinoflagellates "annual plants". And what he means by that – when you go out and look in a drop of water in the ocean, you'll almost always find diatoms. They're there year round. They're always there. They're probably the most important phytoplankton on the earth.

Of that 50 percent of primary production that is created by phytoplankton, they're responsible for half of that. So they have the most primary production of any phytoplankton. Dinoflagellates are considered annual. They're not always there. But when they arrive once a year, or a couple of times a year when the conditions are right, they can make massive blooms of cells. And you'll see examples of that shortly. And in the way these things adapt and try to exist in the ocean – the diatoms, their life strategy is relatively uniform. They all kind of act the same way. But dinoflagellates have amazing and unique adaptations, and that's what I'm going to concentrate on now for a little bit in this talk. I'll circle back to the diatoms at the end, but I was trained as a dinoflagellate biologist so they fascinate me. Dinoflagellates – their name is a combination of Greek and Latin. It means whirling whip. This is a very low magnification – now it's getting higher – of these dinoflagellates.

And as you can see, they can swim. They can move. They have two flagella. One that wraps around their body. One that trails. And it gives this very characteristic kind of rotating motion as they move. On this last shot you can see very clearly this little flagella there. So they're highly motile. Dinoflagellates, as I said, they have really – as a group they have really complex lifeform strategies. And what I mean by that is they can be what we call autotrophic, which means they're straight plants. They're photosynthetic. They can also be what we call heterotrophic, meaning they're not plants at all. They're predators. They eat other phytoplankton. And they do it with feeding nets, and stinging harpoons, and little appendages that can grab other organisms. Here you're seeing a dinoflagellate that has a feeding net out, and it's actually captured a colony of diatoms. It's going to suck the cell contents out of that to survive. There's also a group that are what we call mixotrophic.

They do both. They have chloroplasts. They can photoshynthesize just like a plant, but they also eat things. If they need to supplement their nutrition, they'll go after and eat another dinoflagellate or eat a diatom. We have a great analog for this. A lot of people know what the Venus flytrap is. That is a plant. But when it wants to supplement its' nutrition, it captures flies and other insects and eats them. We also have a group that are born as heterotrophs. So they're born as predators. They don't photosynthesize. But these have learned how to capture photosynthetic organisms and steal their chloroplast, and not digest them but use them. They will become autotrophic. So they're born as animals but they become plants when they want to. Dinoflagellates also can form symbioses with other organisms. Almost everyone knows about this. This is coral. So if we have a coral here and it spawns, it puts out its larvae – as the larvae is developing, it gets infected or it acquires this dinoflagellate called Symbiodinium. Symbiodinium starts to reproduce in the flesh of the coral, and as the coral settles and grows it gets filled with these dinoflagellates.

And all these little brown spots you see in there are individual dinoflagellate cells that live there. And it's truly a symbiotic relationship. The coral gets the photosynthetic product from the Symbiodinium dinoflagellate. It gets the donut, so to speak, and the oxygen that they produce. And the dinoflagellate gets the CO2 that it needs directly from the coral while it's respiring – it's an animal. It also gets shelter and it gets inorganic products left over from the coral eating. So they both help each other. If this dinoflagellate disappears from the coral, we get what's called coral bleaching. People may have heard of this before. And the coral cannot survive without these symbiotic dinoflagellates and they die. Dinoflagellates can also be parasites. They can be parasites on each other. They can be parasites on zooplankton, parasites on fish.

Here's an example of that. This is a regular dinoflagellate. This is a small parasitic dinoflagellate called amoebafibra, which has attached itself to the larger dinoflagellate. It absorbs through the cell wall. It then makes hundreds and hundreds of copies of itself, just like a virus or a bacteria infecting a human. Here's an example of what one of these looks like when it's infected. They look just like an old beehive and you can see it very clearly when you look through a microscope. Eventually they kill the host and they come out with a really large amount of cells. This is called a vermiform stage. This is an actual microscopic plate of one. And then they repeat the process. They spawn out all these different cells. So they can also be straight parasites. How do dinoflagellates reproduce? The normal way is through simple mitosis.

We have a vegetative cell. This vegetative cell doubles all of its cellular machinery. It doubles its chloroplast, its mitochondria. It makes two copies of its DNA. And then it simply just splits into what we call two daughter cells. This is an asexual process. These are exact genetic clones of each other and they just keep on going this way. However, when times get tough, if there is poor growth conditions where they don't think they can survive, or there's heavy predation, or there's these parasites starting to attack them, they go through sexual reproduction in what we call cyst formation. So in this case, its vegetative cell actually produces two gametes. This is equivalent to a sperm and an egg in a higher animal. Same thing. These gametes from different organisms have to find each other. They fuse together. They produce what we would call a fertilized egg or a zygote, and then it goes through kind of a change and it creates what's called a resting cyst. And you can think about this – it's a seed. Here's another example of that same process.

These seeds that they produce – these resting cysts – fall out of the water column and they go down into the mud, and the sand, and whatever on the bottom of the ocean. When conditions are favorable again, they hatch and they repeat the process. The dinoflagellate comes out and it starts its lifecycle again. Here's a great micrograph of that happening. This is a dinoflagellate hatching out of a cyst – becoming the swimming organism and leaving the old cyst shell behind. This is a way for the population to survive for long periods of time. They can be dormant in the sediments for years upon years. It also increases their genetic variability. They're actually changing up their genome. They're going with other organisms and swapping genetic material. A lot of algae do this, just not the dinoflagellates.

And these cysts they produce can persist for decades in the mud. They have found cysts that are still viable 100 years old. Amazing ability to survive. Again, I said phytoplankton they're single cells, no brain, no nervous system. And yet, they can sense their environment a lot like we can. They demonstrate what we call phototaxis. They can sense light with eyespots or what we call ocelloids. Here's a shot of one of these here. This is a dinoflagellate cell and it has this structure called an ocelloid. What they do is they modify some of their organelles to create a rudimentary lens and a retina below it for increased light absorption. They can also demonstrate what we call gravitaxis. They can sense up and down, and I will show you an example of this a little bit later. They can also demonstrate chemotaxis.

They have a sense of smell if you want to put it in human terms. And to show that, this is a microscope shot. This is a pipette tip that had fish oil in it. It was put into a container that was filled with dinoflagellates that are predatory on fish – they actually attack fish and go after their flesh. As soon as this fish oil got in there, the dinoflagellates immediately went to it. They thought it was something they could attack. They knew v they could smell – that that fish oil was there. Dinoflagellates also have circadian rhythms. They can sense time, and I'll show you an example of that in a few slides, as well. Who knows what this is? Bioluminescence. Very good. This is light production. Dinoflagellates are really good at making light. So if you've been down to the beach at nighttime or during the summertime, this is a very common thing. And when you see this kind of bioluminescence where the water looks really milky – it's just not a spot of light here and there – it's almost always dinoflagellates.

There's a lot of things in the ocean that can bioluminesce, but they're bigger and they make just flashes once in a while here and there. When you see this, that's a big bloom of dinoflagellates that are bioluminescing. These are a lot of the causative dinoflagellates that can bioluminesce. Not all of them can, but a lot them do. I've studied a lot of these. This one is pretty important here. This is pyrodinium. This exists in the Indian River Lagoon. So if you've been out there in the summertime, out in a kayak at nighttime and you've seen glowing water, this is what's in the water. It's also toxic. I'll get to that later. So you probably ask yourself, "Why do they produce light?" Again, I said there's these predators that are out there. This is a zooplankton called a copepod.

It's like a lobster, shrimp-like creature. They try to eat dinoflagellates. It's got these big arms. They grasp out. They try to get them. You can see this little mockup. There comes the predator after the little dinoflagellate. Well, this dinoflagellate is bioluminescent. When this copepod tries to grab it, the cell flashes. When you touch them, it's that mechanical disturbance that makes the flash. These can sense light too. And that light flash startles them. They let go and they swim away. The thing survives. There's also what we call the burglar alarm defense. When this flash occurs when a copepod is trying to eat a dinoflagellate, that flash attracts much bigger fish. They're attracted to light in the ocean and they may eat the thing that's trying to eat the dinoflagellate. So they have two ways of getting rid of their predators.

So how do they produce light? This is a micrograph of a bioluminescent dinoflagellate I did back in 2000. It's very interesting. I'll have to walk you through it. There's three panels here. They represent the daytime, the transition between day and night, and full nighttime. This top panel – this red glow you see in the cell – is where the chloroplasts are. That's the photosynthetic machinery. When you hit cells with a certain color of light, they actually flash red light. It's called fluorescence. So we can image where the chloroplasts are. This is just the light micrograph – what the cell looks like in the light of all these cells that are shown here. This is the bioluminescence. We can chemically stimulate the bioluminescence. We can just make it put out its light. So during the daytime, you see the chloroplasts – the photosynthetic machinery – are spread out all over the cell. It makes sense. They've got to capture light. They want to increase that surface area.

They want the chloroplasts spread out everywhere. The bioluminescence, however, is very dim and it's only in the dead center of the cell around the nucleus. It makes sense. They don't create bioluminescence during the day. You can't see a flash if the light is bright. It does them no energetic benefit to do it. In the transition when it just turns nighttime, you can see the organism is pulling back all its' chloroplasts. They're streaming back to the center of cell. They do this through microtubules, and microfilaments, and their cytoplasm and they stream them all back. They know when to move them. The bioluminescent organelles called scintillons – they're little organelles that make a chemical reaction to produce light – they start to increase in number and spread out from the center of the cell. When we fully get into nighttime, all the chloroplasts are centered around the nuclear area of the cell, and all the scintillons, or the light producing cells, are now spread out like the chloroplasts were during the day. So they're ready to go. They're ready to make a really bright flash.

It makes sense why they have to do this. If they had these chloroplasts out at the same time during the nighttime, their own pigments would absorb their flash. They'd lose that light. So they have learned how to control this. And their circadian rhythmicity I told you about, this was how we actually first demonstrated that they could sense time, that they had an internal clock. If you put these things in the dark – you never give them a key for daytime – and measure the amount of bioluminescence and what this looks like day after day, they will keep on doing this without any light signal at all. Right when it would have been light, they know. So they do sense time. I'll show you another example of that a little bit later. Dinoflagellates are kings at making toxins. A lot of algaes do, but the dinoflagellates make an array of toxins. Why do they do this? The first reason is what we call allelopathy. This is essentially chemical warfare on their competitors. They produce chemicals that – this is one as an example of this.

This is a dinoflagellate that was put in with another dinoflagellate that makes a chemical. It's allelopathic to it. This dinoflagellate, once it's exposed to this chemical, it starts to swell. It swells, it swells, it swells, it bursts and it dies. It's one way of getting rid of your competition. You poison them. Another reason why they do it is for predator defense. Again, like bioluminescence, they're trying to stop things from eating them. A lot of these toxins they produce when these copepods eat them, it suppresses their feeding response. They just don't want to eat. They feel sick. It also stops their reproduction. It totally stops their reproduction. So it essentially is poisoning them so they're stopping their predators from growing and increasing in number.

It also can decrease their motility, so that when they eat these things, they become slow and lethargic and now other things can eat them. So they've got their number. They can get rid of them. This toxin production is obviously a problem for us. That's why we have what are called harmful algal blooms. We used to call them red tides because some of the early ones that were identified were very red. This is what the water looked like. You'd look out there and go, "Oh, my God, what is going on?" But not all of them are red. You can have green harmful algal blooms. You can have brown ones. These two shots are actually from the Indian River Lagoon. So this is a Microcystis bloom that occurred, I think, last year. This is the brown tide that I think is currently occurring up in the northern part of the Indian River Lagoon. These can be devastating to local wildlife and local plants.

The reason is the host of toxins that come with many of these organisms, and these hurt us as much as they hurt other animals. There are dinoflagellates that give you paralytic shellfish poisoning. Pyrodinium, one of the dinoflagellates that's common out in the IRL, actually does this. I think that's why there's now a constant ban on puffer – you can't harvest puffer fish anymore. There's also diuretic shellfish poisoning. There's neurotoxic shellfish poisoning. There's amnesic shellfish poisoning. This actually comes from a diatom. All these different poisonings, what it sounds like is what they do to you. There's also ciguatera fish poisoning from dinoflagellates. This is pretty common down here in the tropics. We also have Microcystis that I talked about. This occurs in the Indian River Lagoon, Lake Okeechobee, a lot of fresh water bodies. It's a big problem in Lake Erie.

I don't know if you were watching the news – I think it was last summer or the summer before – the whole city of Toledo – millions of people – could not drink their water because a massive bloom of this stuff got into their drinking water supply. And it's nasty. And the lake is just covered with it. It happens here to. It produces a hepatotoxin and this is a liver poison. Very bad for us. So they don't have to be poisonous. There are some diatoms – I don't know how clearly you can see this, but there are a lot of little serrated edges on the spine that grows out of it. When these get into fish gills, they cut the gills and the fish produces mucus and eventually it will die, or basically suffocate. So it's a mechanical destruction of the fish. This causes massive fish kills out in the Pacific Northwest. We also have brown tides. We have these here. They occur in Texas.

They've occurred in Rhode Island. The organism is not necessarily toxic, but there's so much of it and it absorbs all the light coming in when it's at the surface that nothing below it can grow. So any of the seaweeds, any of the algae that's on the bottom – the seagrass here – it dies for lack of light. But these brown tides also produce a mucus-causing compound, which necessarily doesn't kill shellfish, but it causes them not to feed right and they starve to death. So it can be devastating to oyster fisheries and other things. Also, anoxic water is produced by these. You can imagine when you have a ton of this stuff, like here, in the water, sooner or later it dies, and it rots, and it drops to the bottom. When that stuff is rotting, it eats up all the oxygen in the water so it becomes anoxic. And any organism that can't get out of that water fast enough is going to suffocate and die. That's another common thing. We have massive dead zones in a lot of the ocean due to some of this.

Now that I've shown you all these adaptations, we're going to go through a few examples of how these are used to thrive and to compete. How do they use them? That's what we call form and function questions. I'm going to remind you of this vertical ocean again. For phytoplankton, they really need two major things for growth. They need light and nutrients. If we go back to this simple diagram with depth, light decreases with depth, nutrients are generally low at the surface and they increase when you go down in the water. Usually for many phytoplankton, there's a sweet spot where there's just enough light and just enough nutrients, and that's where they're going to grow best. That's their little niche and they've got to get to that sweet spot. How do they do that? How can phytoplankton change their vertical position? Well, you already know. They can swim to where they have to go.

I said before that diatoms aren't motile but they change their buoyancy. And they can use this to find an area in the water column, or essentially float to an area in the water column where they may grow better. And they can maintain themselves at a particular depth for very long times. They just don't sink out of the water column. I'm going to show you an example of this for dinoflagellates. This is work we did in 2010. I'll have to walk you through this graph but this is depth going down. So this is depth in meters in the water column. It's about 45 or 50 feet. And this is the year day on the x-axis here. So this represents about 14 days of continuous data. What this green trace is, is the chlorophyll fluorescence that we measure in the water column. It indicates where the population of phytoplankton are in the water.

This water here, where this thing is going up and down, was almost entirely dominated by this one species of dinoflagellate called Akashiwo. You can see every day it's going up down, up down, up down. If we average this over this entire 14-day time period, where the population is versus time of day for a single day, this would be the dark periods, this would be the light periods, this would be noon. Zero and 24 are midnight. This is the kind of curve we see. We see that the population is down at depth at night. It comes up, sits at the surface for a while, and then goes back down. This entire population moves synchronously with what we call diurnal vertical migration. They're demonstrating a whole bunch of these things I've already described. So they're doing circadian rhythm here.

Look at where they are. They start their journey up to the surface way before the sun comes up. So they know this is a long journey. They've got to go. It's time. So they are already set. They know what time it is. They have an internal clock. But they're also showing gravitaxis. They know which way to go. There's no light to tell them where up is. They know which way is up and they swim that way. They're also doing phototaxis. When they get into the light, they go to a certain light level. Too much light can be damaging for a phytoplankton. They can have an optimal light level. So they can actually go to a specific place and kind of stop there. They're also doing chemotaxis. What was happening when we were out during this bloom is that all the nutrients were down here. They were deep in the water column. So what these were doing was going down at nighttime, taking up the nutrients they needed, and then going up during the day to get high light to grow and photosynthesize.

And they would stop right about where the nutrients were high enough they could uptake it. So they were doing chemotaxis. They knew when they hit the nutrients they needed. Just for reference, this little journey this little tiny microscopic organism does is about 200,000 body lengths per day. If we scale that to us, that's like us swimming 400 miles per day every day. It's an impressive thing for this little guy to do. Because these organisms move synchronously, they can control their position, we get what are called phytoplankton thin layers. The whole population can be in one small area of the water column that can be that sweet spot where they need to grow. Here's an example of that also from Monterey Bay. This is the chlorophyll or this represents where the phytoplankton are – their biomass – so if it's high there's a lot of them. This is the density in the water column. You can see that most of the population is sitting at this little tiny area around ten meters and the whole population is in an area about that big.

You've got to ask yourself, "What ecological benefit is there to doing this?" forming these thin layers? And these are really common. They occur everywhere. Why form thin layers? Well, I told you the first one. It's a resource gradient exploitation. They're trying to enhance their growth by getting into that sweet spot of light and nutrients for whatever they need. But also, I told you about the heterotrophic organisms. So if the photosynthetic organisms are making a thin layer, the ones that eat them have to go there and find them. So they'll do it too, and you'll get a thin layer on top of a thin layer of a different species that's trying to go after them. They also do it for competition and defense. They create these allelopathic substances and toxins. If you're spread out through the big ocean and you're a single cell putting out this toxin, it's not going to be very effective. But if you can concentrate yourself, you can make a really high concentration of that substance or the toxin, it's going to be a lot more effective.

It's the same thing with bioluminescence and the shading effect. If you get a whole bunch of algae that are sitting at one depth, just like the shading that kills seagrass in the Indian River Lagoon, they're absorbing all the light that hits that layer. All their competitors below them that are going to use their nutrients, they can't grow. They're shading them out from growing. Lastly, sexual reproduction. They form gametes. They have sperm and eggs, so to speak. Again, if they're spread out through the entire ocean, these little tiny microscopic organisms aren't going to find each other very easily. But if they're in close proximity in one of these little thin layers, they can find each other relatively easily. So it's a big part of their ecology for doing this. The last thing I'm going to talk about tonight is a question that has also pondered plankton ecologists for a long time. And that is, why do we have such amazing diversity in the shapes of these diatom colonies? These are all diatoms and these are all colonies.

Look at these. You have these spirals. You have these amazing chains that can be flat. You can have these ball-like structures, these big needle-like colonies. Why do they do this? There has to be a reason. Nature always has a purpose. We think we know one of the reasons why. There's been a lot of hypothesis. But to get to the reason why, I have to detour through this project. Our lab created what's called a holocam. This is an underwater holographic video microscope. It images undisturbed volumes of the water. So it's not like we have to take a sample, and put it on a slide, and look at it under a microscope. It looks at an open area in the water and it images all the phytoplankton that are in there, undisturbed, so we can look at them in nature. It has a magnification that can see over the whole range of phytoplankton sizes. Just to reiterate what Dennis said, if you want to see more of this kind of cool instrumentation, Mike Twardowsky, who I work with a lot is going to give next week's lecture on a lot of this stuff. So what is a hologram? Very simply, if you have coherent light and it hits a particle, it creates a defraction pattern.

It's the scattering of the light when it hits the particle, and it looks like this. If we represent this form mathematically, we get a shape that looks like this. The envelope of this encodes the size and shape of all the particles in that hologram. All these high frequency oscillations encodes its location in 3D space. So we can get all this information from a hologram. We use what's called inline digital holography. What it is, we shine a laser into an open sample volume of seawater. And on the backside of that, it creates this scattering defraction pattern. It's very simple. And we record these with a camera. I could create a holography system with this laser pointer and my cellphone camera. It's that simple. If we put a microscope objective in front of our camera, we now have a digital holographic microscope. It magnifies the hologram. The advantage here of a holographic microscope is it images volumes that are two to three orders of magnitude greater than a standard light microscope. A standard light microscope is great but it only can see a very narrow focal plane. When you use a hologram, you can see everything at once through a large volume.

The trick in holography – creating the system is easy. The trick is in the processing. This is what's called holographic reconstruction. Once we put our system out and we collect our holograms, we have to do this mathematical reconstruction. It's called image sectioning. It creates in focus images of all the particles that were in this original volume that we created this hologram from. I will not go through the math. You don't want to know. This is us flying through the image planes of a hologram. This is a dinoflagellate culture. They're kind of small. You can see ones that are out of focus are coming in focus. We're moving in 3D space and seeing all these particles that are in this big culture all at once. Single hologram – after we reconstruct it, we can see all of these and where they are in free space.

It's a really impressive technology for understanding plankton in the ocean. So we deployed this system out in Eastsound, Washington in 2013, and actually also in 2015 in September. And we looked specifically at one of these phytoplankton thin layers, where there's a big aggregation of phytoplankton at a depth. So we see it here. Again, this is chlorophyll here and this is the density of the water here. And you can see this big population or this large amount of chlorophyll sitting right around two and a half, three meters depth. And then it's kind of the same all through the water column. We're going to look at two depths with the holography system. We're not going to look at a reconstructed. We're going to look at the raw video feed from this system. First, we're going to look down here where it's all kind of the same. This is the raw video feed from the holography system. This is seven millimeters by seven millimeters so it's a pretty big volume of water when you're looking at microscopic organisms. You can see there's a lot of cell fragments going by.

A lot of these big things are diatom chains. A lot of what we call detritus in here. There are aggregates of dead material and a lot of little specks of possibly re-suspended sediment from the bottom. But let's see what's in this thin layer. This is what's there. You can see there is a massive amount of this big, linear, colonial diatom chain. And does anyone notice anything unusual about this as it goes by the screen? Remember this is looking at it in free space. These are just flowing by a camera. They're oriented. They're all going the same way, and they're actually all oriented horizontally. The camera was slightly tilted when we took the picture. So all of these diatom chains that are in here are all oriented horizontally with respect to the downwelling light field. It was dominated by this one species here.

It's a chain-forming diatom called Ditylum. How do they orient? And if we look at the two states of the ocean – we can have turbulence if you have a breaking wave or the surface of the ocean. It's very turbulent when the wind is blowing. And if this is the water just spinning around and mixing everything, everything in the water is going to be randomly oriented. It's just being mixed up like a blender. However, most of the time the ocean is not in this state. It's in a current shear state. The currents of the ocean move horizontally and they move at different velocities as you go up and down through the water column. This creates a velocity gradient than what we call current shear. And when these organisms that have a big aspect ratio – they're big, long, thin things – they actually line up parallel to the current streamlines. And that's exactly what we were seeing.

We went out there and measured the shear and they were perfectly right on a shear level. So the shear was making them all line up. Why do we care about orientation? So now I'm finally getting back to trying to answer the original question I started with. If we look at the amount of light a phytoplanktor could absorb – so the light is coming down. They can be horizontal like all the ones we saw, or they could be anywhere from tilted, tilted all the way to vertical like this. If you look at the amount of light or photons they can absorb versus the angle from horizontal – so here they're horizontally, here they're vertical – it goes down a lot. If you compare oriented cells to randomly oriented cells, they can increase their light capture when they're oriented by 40 percent. That is a huge number. They can grow a lot better. We have a perfect example of this for plants on land. It's called phototropism. Everyone who has grown a plant has seen this.

You put them near a north-facing window, what do they do? They bend over to the light. What are they trying to do? They're trying to increase their light capture. It's important. They're plants. They need light to survive. They will go to the light. Oceanic phytoplankton don't have the benefit of soil and stem. They can't move. So why are they doing this? It's form and function. They have evolved to actually just do phototropism using what they have. They've got the motion of the ocean and it's letting them do it, which is fascinating. It may be why we have all these shapes. It's how they interive biophysics, essentially. Our lab is incredibly interested in this. We do a lot of it. Among other things, we just got back from the National Oceans Sciences meeting where we did a few presentations on this. Both of these were done by post docs in our lab – Adi Nayak and Malcolm McFarland – we recently published a Sea Technology article on all the kind of instrumentation you need to look at particles like this in the ocean undisturbed.

Mike's going to talk about this week if you're interested. I've just got to say, a lot of this kind of work can't be done without a great lab, and we have a great lab. Here's a picture of most of the people in our lab. This is Malcom McFarland, my post doc. This is Schuyler Nardelli. This is Nicole Skyler. This is Adi Nayak, another post doc. This is actually Fraser Dalgleish. He's another professor here. The only person that's missing on this is Mike Twardowsky but he'll be here next week. I want to leave you with this. When you look out at that great big ocean, just remember in a single drop, there is a world of survival going on there. These things have all kind of adaptations to try to beat each other, and compete, and dominate. And we need every single one of these little drops with this universe – world of competition going on, we need it. They are incredibly important.

And I will stop there..