by Dr. Steve Strand

NOAA Classroom Exploration of the Ocean Virtual Teacher Workshop Sep 27, 2004

HI, I’m Dr. Steve Strand, and I’m going to talk tonight about jellies. And this is an interesting group of animals because these are really ancient animals. These are some of the first multi-cellular animals on the planet.

As such, a lot of the major innovations that we now take for granted, things that we think are just part of every animal, were invented by this group. Things like tissues and organs, and organ systems were innovations that this bunch of creatures came up with and passed on down to the rest of the animal kingdom, including those sitting in this room. Nervous systems were invented here. No nervous systems before these guys came along. Contractile tissue is known to the rest of us as muscle. These are the guys that invented it. Digestive systems, mouths, things that we really take for granted were all part of what this group evolved.

There are two groups of jellies I’m going to talk about. I’m going to talk about both of these because they’re similar in many respects, even though they’re separate phyla, and their probably very separate evolutionary range. There’s a group called the ctenophores. We won’t spend too much time on them, but we’ve done some research on them, Bill and Peggy, Pat and I, and a number of other people. They’re a remarkable bunch of animals. You see them in aquaria. They’re some of the prettiest animals on the planet. And then the phylum Cnidaria. And these are the, if you want to say, true jellyfish. And of course, some people think jellyfish shouldn’t be called jellyfish ’cause they’re not fish. But I even call sea stars starfish, so it just depends on how much of a purist you are.

Jelly research is so interesting. First of all, there’s no animal cruelty issues. No one walks around with signs saying, “Save the Jellyfish.” No one cares, as a matter of fact; it’s hard to know how to be cruel to a jellyfish, which is kind of nice. We deal with less paperwork than if you study primates. They’re not very fast, and they’re usually not hard to find. And they don’t tend to get away once you find them, which are all attributes.

On the other hand, it’s really difficult to mark them. The magic marker doesn’t stick, and you put tags in them, the tags fall out, and the jelly fish falls apart. So it’s difficult to sort of follow along and figure out who’s who. And it’s very hard to keep them in captivity. Peggy Hamner’s husband, Bill [UCLA], probably knows more about keeping jellies in captivity than anyone else around. The tanks that many of you will see up at the Monterey Bay Aquarium in a couple of weeks, Bill designed those tanks. He invented the idea and other people have done it.

But it’s really hard because the jellies evolved in a world without walls, without edges. When they find walls or edges, they run into them, and they bang themselves up. And they’re so fragile, that in very short order, they’ve torn themselves to pieces. It’s not just jellies– the big sharks and the big tunas have the same problem. They simply didn’t evolve in a situation where there were hard edges. And as such, they don’t know how to deal with them.

So, you need specialized containers, and the containers work because the edges of the containers have the water moving very fast. So when the jellies hit that, they get blown off that sharp edge down into the middle of the waters going slower. But it means the containers are very constrained as to how they can be designed. And while we’ve done a fair amount of work with jellies and tanks, none of it’s been really very satisfying. So mostly we do field work on jellies, or they take them up and grind them and put them into DNA extractors, which is sort of disgusting. But you do learn answers that way.

So, first of all, the Ctenophores. This group swims along with rows of fused cilia. And it’s this cilia group that reflects sunlight, and reflect rainbow patterns. As such, when you see these on the water, someone goes oh my, look at that, feelings that you get right away. They’re all predators. They all eat something else. A lot of them eat small zooplankton, things like fish larvae and copepods, and other little animals in the ocean.

A few are very specialized jellovores, which is sort of an interesting way to make your living. It’s hard to think of one jelly eating another jelly, and yet it’s a very common thing that we see.

Many of the Ctenophores fish with these kinds of rows of tentacles like this, with little sticky cells on them to catch small prey.

They don’t have the nematocysts or stinging cells that the Cnidarians have. None of the Ctenophores have any ability to sting you or I or anybody else.

I’m going to spend a couple minutes talking about this animal. And if you can pronounce that name, you’re better off than I am. It’s pronounced Mnemiopsis. and Mnemiopsis is a ctenophore that feeds on zooplankton. And it got introduced to the Black Sea, probably in ballast water of a ship from the East Coast of the U.S., because that’s where Mnemiopsis is native.

And Mnemiopsis is a very good predator. When it got into the Black Sea, it thought it had died and gone to heaven, because there was so much food there, so many fish larvae, so many fish eggs that very quickly, it became a problem.

This is what its food looks like. You can see little fish larvae here with the yolk sac, and there’s some other bits of zooplankton. Well, Mnemiopsis is an incredibly efficient predator. By 1989, the multimillion dollar– in fact, I’ll say the hundred million dollar anchovy fishery was gone because Mnemiopsis ate every single larvae. The adults only live a couple of years, so if you eat all the babies, pretty soon you don’t have a fishery anymore. So Mnemiopsis simply came in and ate them all up.

It’s been a major issue. A lot of people spent a lot of time thinking what can we do about this? We used to have a fishery for sardines and now we have a bunch of jellies that no one will eat, and aren’t good for anything. You can’t sell these guys. To give you some idea of how fragile this animal is– he’s not this big, he’s about this big– but if I took my hand and go like this at this distance, he’d break up into a million pieces. This is a big diaphanous fragile animal. And yet it’s quite capable of stripping the water clean of all zooplankton.

Something interesting happened recently– there’s another ctenophore I’m going to talk to you about called Beroe. Beroe is a really wonderful animal that’s basically a bag. The front end of the bag opens up and has a bunch of fused cilia that work very much like an electric carving knife; they’ll go back and forth like this. And they can cut through other jellos.

So this is the front end of the Beroe who’s trying to eat something. And it’s just a big opening like this.

Well, imagine that whole thing can sort of blow its way right through a jello. And they’re quite good at it. Well, Beroe, in 1997, got to the Black Sea. It wasn’t introduced on purpose, we don’t think. But it got there and immediately started eating Mnemiopsis, and eats lots of Mnemiopsis. It really likes Mnemiopsis. And it looks as if the Black Sea ecosystem is starting to recover. We’re finding more and more zooplankton. They’re not fishing sardines or anchovies yet, but they may in a few years. So we observe an ecosystem recovering because of a second introduction, inadvertent but it looks as if it may be a happy ending to sort of a funny story.

And that’s really all I’m going to say about Ctenophores. They’re a neat group. You’ll see them at aquaria. And you can tell they’re Ctenophores, because you see these rows of ctene reflecting the sunlight.

Okay, Cnidarians. This phylum includes the things called the true jellyfish, again, maybe a misnomer but we’re stuck with it. Again, mostly predators. Not all, and they have a very specialized cell type, called a Cnidocyte. Only members of this phylum have this cell, and essentially all members of this phylum have this cell. This cell contains a little organelle called a nematocyst. And there is an organelle that shoots out a little dart and stings you. So if you get stung by a gelatinous animal, it’s not a Ctenophore, it is indeed a jellyfish.

Like the Ctenophores, they do not have a central nervous system. They don’t have anything resembling a brain. But they do have a net of nerves. You could imagine sort of a net or lattice-like structure over this animal. And somehow that nerve net coordinates the animal. Some of these jellies actually have eyes. In fact, they have image forming eyes, fairly similar to ours.

This phylum has two basic body forms.

One of the body forms is a polyp (near left).

The other form is this medusa (far left)

It involves seeing things like this, anemones, corals have this shape. And it’s basically sort of a cupped tentacle at the top, an opening in the middle called the gastrovascular cavity, pretty straightforward.

And the medusa is essentially this cup turned upside down, the tentacles modified a little bit. But it’s the same basic plan.

The polyp is attached to something. Medusas are generally free swimming, but remarkably little changes to come up with a very different plan.

This is a funny cell called the Cnidocyte (right).

Inside the cell is one great big organelle which is that nematocyst (below right).

And nematocysts vary hugely in their power, and in their toxicity. How many of you have stuck your hand in a sea anemone and pulled your finger back? Okay, what does it feel like when you pull your finger back? It kind of feels kind of sticky. And those are all those little nematocysts that were in the outer layer of the skin that are breaking up. You’re breaking like little tiny threads. It’s no big deal.

Years ago, I took a group of kids on a field trip to the beach, and I was telling them about this. And I said, but if it was to hit your eye or your tongue or something, it would be very painful. So there was a kid that naturally had to put his tongue on the sea anemone. And it was pretty interesting, because his tongue swelled up to exactly fit the inside of his mouth. And then it stopped swelling. And he didn’t die. That was the good part. But it was amazing. It turns out that the toxin in the anemones is fairly significant, if it gets into a bloodstream.

This is a little bit of a drawing from the New England Aquarium showing how this thing works. You inject this little stylet, and then of course the green toxin, which probably wasn’t really green, injects like that. But it’ll give you some idea. There’s a little coiled thread inside there.

Imagine, some of these animals produce toxins heavy enough that they can kill a human being in less than an hour. Others including many of the jellies we’ll be talking about here, you can swim through them all day, and you can tell they’re stinging you, but it isn’t really even irritating — so highly variable.

Okay, so three groups of Cnidarians. There’s the corals and anemones, which are called the Anthozoans (example, right). We’ll talk just briefly about them because they’re not really jellies at all. There’s the Hydrozoans (below), which are a weird, very bizarre group, a lot of colonial forms. As a species, we don’t understand colonial things because we can’t empathize with something that’s built up in colonies.
It’s just too different. Things like the Portuguese Man-o-War, Vellella, some of you may know. Often, both polyp and medusian. Sometimes some other things that don’t fit any of our definitions.

And finally, the true jellyfish are the Scyphozoans (farther below). So, corals and anemones, the Anthozoa. And the only reason I put this here was to tell you there’s no medusa phase, there’s no jelly phase. And think about the anemones and corals you’ve seen– almost always are colored, aren’t they? Those colors are symbiotic algae living inside their tissues. So these guys, while they are capable of catching prey, and indeed do catch prey, have a fair amount of their energy derived from their photosynthetic commensuals or symbions, mutualists actually. Anemones, corals, neat bunch of critters but not part of today’s talk.

Hydrozoans, again, the strangest bunch. They have things like this little hydromedusa here that look very much like jellyfish. They’re things like the Portuguese Man-o-War there, which is a very strange animal that doesn’t fit any of our definitions. Many of them are of this colonial thing, different individuals, different tasks.

Imagine there’s individuals that just produce, that float. There’s others that create those tentacles. On the tentacles, some do digestion. Others do food getting. So a very, very complex array of things, but they’re all individuals. They simply specialized out their tasks. We just don’t think like that. We don’t live like that. So it isn’t part of our world.

There’s one group of these animals I really have to tell you about. That’s the Siphonophores. These, many places in the open ocean, are the most important predators, okay?

This is, on the right, is sort of a swimming head of the bell of this thing. Imagine that’s maybe two, three, five, six inches long. Trailing behind this are tentacles in the 100, 200, 300 foot long range. The tentacles are covered with little small hairs that are full of stinging cells.

These guys are capable of catching fairly large prey. And in the open ocean, in mid-water, they’re often the dominant animal down there. So these are very important mid-water predators. And then there’s Vellella, the By the Wind Sailor, a funny group of things, some of which form a jelly category, some of which don’t. Occasionally, Vellella washes up on the shore in wind drogues that are two and three feet high. Often, though they live way offshore as well.

And finally, there’s the Scyphozoans. These are the real jellies

And the Scyphozoans again, are a very diverse bunch. This is in many ways the weirdest Scyphozoan. This is a jellyfish upside down. What you’re seeing are the tentacles. And what you are seeing here is a whole bunch of tissue that’s kind of brownish. It’s brownish because just like corals, this jellyfish exposes its underside to the sun, and farms algae.

It has nematocysts and it can sting, but it doesn’t spend much time fishing. It lays on the bottom, and sometimes the bottom for acres and acres is covered with these jellies, all very slowly pulsing. And they’re simply photosynthesizing. They’re just farming algae. These guys are farmers.

However, most jellies are indeed hunters. This is a beautiful Pelagia here. This is an animal we see off our coast all the time. It’s often got– these guys get sort of this big around. They’re great big beautiful creatures. Lots and lots of jellies, they range in size from a couple meters down to just a few millimeters. And not too many things eat them.

A little bit about jellyfish. Most of the jellies have an alternation between the polyp and the medusoid phase. They switch back and forth between the two on an annual basis, which again is something that’s sort of odd for us to think about. The best analogy I can give you are plants, things like desert wild flowers. They spend part of their time as a seed, part of their time as a plant.

Well, jellies spend part of their time as a medusa, part of their time as a polyp. So imagine, summertime, we’ve got these jellyfish swimming around very happily, male and female. Along comes the fall, and they start to mate. They have sex.

And they produce fertilized eggs that produce this little thing called the planular larvae. The planula larvae swims to the bottom. And by winter, we have this little tiny polyp sitting down there. As springtime comes, this polyp starts to divide across the surface like this and make these little tiny Ephyra, which is just a baby jellyfish. So they spend their winter on the bottom, hanging out, not doing much growing because there’s no food. Spring comes, little jelly, lots of food in the water. They grow up, they have sex, and it goes on around. The question always is of course, how do they know who’s who? And no one seems to know the answer to that.

If we take jellies, and we put them in a tank in an aquarium, they’ll live three or four years. They don’t die in the fall because they’re programmed to die. They die because the food’s gone, and that’s just the normal life cycle.

So now we’ve got an animal with no brain. And I’m going to talk a little bit about some complex behavior which is migration and navigation. So you wouldn’t think an animal without a brain could do anything very complicated, because normally we think of complex behaviors as the result of complex nervous systems. As a matter of fact, you can look at any book on behavior and they start out with a shrew brain and work up to a human brain. And they show the shrews are dumb and humans are smart. And that’s probably generally true.

So how does something like this evolve? I’m going to talk very specifically about some work that Bill and Peggy and Pat and I did, up in Saanich Inlet, which is in British Columbia. And this started out because of some funny aggregation of jellyfish that we found

This is a picture we took in the water in Saanich Inlet. These are Aurelia aurita which are a jelly about this big. Okay, pretty good sized animal.

There were 30 jellies per cubic meter of water. So this much water had 30 of those guys. In fact, they were packed in about as solid as you could pack jellies in.

And we asked the local biologists about this. And they said, oh yeah, the current’s bringing in these bays, and they get stuck there. They can’t get out. And I said, oh. And Bill said, that doesn’t sound right. So we asked the question, is that true?

This is a map of Saanich Inlet. That’s what it really looks like. The black dots show where we were finding Aurelia. And when we started thinking about this– and this really was Bill’s. I have to give Bill credit here because he got very, very skeptical about the currents driving these jellies in like this.

So we put some drogues in the water– a drogue is simply something that floats with the water mass, but has a little flag sticking up so you can see where it’s going.

We put these drogues in the middle of jellyfish aggregation. The next day, all the jellyfish were still in aggregation, and the drogues were way out here in the center of the bay, a half a mile offshore.

So clearly, the jellies were not being kept in these bays by the currents. As a matter of fact, the currents were looking to move the jellies out, and the jellyfish were staying in the bay anyway.

At this point, this became pretty interesting because somehow the jellies were staying there– you know, you might say they don’t have free will, but I don’t think they had free will.

So, this was sort of terrible place to spend the summer. It rained one bay that summer, up there. But the jellyfish aggregations like this were very stunning.

What we noticed was that when they were in these really dense aggregations, they simply swam slowly down until they got close to the bottom, they turned around, they swam slowly back up, which is pretty boring. That’s all they did in the aggregations. If there weren’t any aggregations during the day, they always swam southeast. Not 100% but enough to convince us that they were swimming southeast. At night, wherever they were, they just swam slowly up and down.

So this was curious, but we still weren’t sure what was going on. And really, the first clue came about– we had a couple of overcast days; we had a day of rain. We got these overcast days, and the jellies that were out in the middle of Saanich Inlet, stopped swimming southeast, and they started just swimming slowly up and down. So these are the kind of data we were taking.

And this (right) is just showing what happened over the course of the morning. It was early in the day, 6:30, 7:15, 9:15. The jellies were moving in all directions. This is just a compass rose, and there’s no vector here. The sunlight hits the water at 8:30 and all the jellies swim southeast. At 9:45, they’re swimming southeast. And at 5:00 that evening, they’re still swimming southeast.

So, they’re pretty good at navigating.

If you think about this, if you want to swim in one direction, and you’re using the sun as a clue, what are the two things you need to know?

Where is the sun? and What time is it?

Because remember the sun’s in a different place during the day. So you have to know what time it is, as well as where the sun is, right? With those two factors, you can do sun compass navigation. Without those two, you can’t. So Aurelia have the ability to detect the direction of sun, and to figure out what time of day it is. They don’t have to Casios or Timexes. They’re doing this with some kind of internal clock, which by the way, virtually every animal on the planet has.

So then we have to ask, why? Why would you spend a fair amount of effort to get into these really dense aggregations, and then swim slowly up and down? And actually, for a while, we were really puzzled by that. So we started going back and looking at these aggregations. And what we found was sort of interesting. A large number of the animals have these long white strands coming out of them. And by long, I mean three, four, five meters. And they were about the diameter of a human hair.

So, they’re pretty good at navigating.

If you think about this, if you want to swim in one direction, and you’re using the sun as a clue, what are the two things you need to know?

Where is the sun? and What time is it?

Because remember the sun’s in a different place during the day. So you have to know what time it is, as well as where the sun is, right? With those two factors, you can do sun compass navigation. Without those two, you can’t. So Aurelia have the ability to detect the direction of sun, and to figure out what time of day it is. They don’t have to Casios or Timexes. They’re doing this with some kind of internal clock, which by the way, virtually every animal on the planet has.

So then we have to ask, why? Why would you spend a fair amount of effort to get into these really dense aggregations, and then swim slowly up and down? And actually, for a while, we were really puzzled by that. So we started going back and looking at these aggregations. And what we found was sort of interesting. A large number of the animals have these long white strands coming out of them. And by long, I mean three, four, five meters. And they were about the diameter of a human hair.

So we took some of these. We took them back to the boat. We stuck them under a microscope. And under the microscope, there were all wriggling little things. I said, those look like sperm. They were sperm. So these strands, are very densely packed. These sperm strands are very densely packed with sperm.

What happens is, the males, in the aggregations only, swim slowly up and down with these strands. The females come along and grab these strands– and they don’t know sperm from food– they grab these, they move them into their gastrovascular cavity, which also serves as a place where their ovaries are. The sperm get in there. They know they’re not food. They know what they are. They find the eggs and they fertilize the eggs. So it’s a very interesting system.

If you get the males outside these aggregations, they don’t produce sperm strands. So literally, these guys are coming together to mate, which makes perfect sense. So really, they use sun compass navigation to navigate these bays where they’re super-dense, where they can find a willing partner. But of course, they don’t spend much time choosing each other. They simply run into sperm strands.

In one particular fjord, they swam southeast, in order to find other Aurelia. They’re going to be able to mate. Come the end of a season, they can settle out on the rocks. And the next season, as long as they swim southeast again, they can stay in that same fjord.

Now they do this whole thing without a brain. They probably don’t contemplate it very much. And they probably do it for a very long time. The question is what do they do other places? What do they do in fjords that open up to the south? Are there jellyfish aggregations– I just learned there are. We’re going to go back up this summer and see if we can figure out the genetic or behavioral component to this thing, because we really don’t know what’s happening.

Jellyfish don’t just aggregate in that one spot. As a matter of fact, around the world jellyfish blooms are becoming a real issue. I wanted to spend a little time talking about this animal here. Pat and I had the good fortune of spending time with Bill and Peggy out in Palau last summer. And this animal here, which is– the genus is Mastigias which doesn’t mean too much. But anytime you see this brown color, be real suspicious. These are plant cells. These are algae. These are symbiotic algae, zoozanthellae in there.

And the Mastigias, in marine lakes of Palau have these algae. And they do sting, they can sting, but the sting is so faint that you can feel it on your lips or your face, but you put your hand in there and you can’t feel it at all. Because they’re not hunters. They’re farmers. They still have the stings because they’re evolutionarily endowed with them. But they’re no longer an important part of their biology.

This is a nice aerial photo of the lake. And I don’t know if you can make out the jellyfish swarm here or not, sort of like this. But what happens here is the jellyfish move in these lakes in such a fashion as to do two things.

They don’t want to hit the edges of the lake, because the edges are full of predators. The predators in these lakes are anemones. They’re all the same phylum; it hardly seems fair. But the edges of the lake are just covered with anemones who eat those jellyfish who make a mistake.

And of course, the jellyfish also want to stay in the sun.

But the big issue they have is if they move into the shade, they’ll hit the edge of the lakes. This is showing you just the edge of a swarm here. And literally, that solid of jellyfish that if you move through, is almost unbelievably dense. They don’t sting bad so it’s not a big deal.

Over here, there’s almost no jellyfish. So they’ve formed, literally, this wall at the edge of the light. And as the light moves, the jellyfish move to stay in the light.

It’s really a remarkable system. The fun thing is, in this particular system, that the jellies in this top layer here are essentially farmers. They’re all feeding by farming algae. Underneath these, is another species of jellyfish which you’ve already heard about. That’s Aurelia. And the Aurelia down there are hunters. So there’s a thermal cline, a thermal break in the lake between here and here. Up here, you’ve got jellyfish in the sun. As they move, they slowly twist like this as they go. And by doing that, they’re able to keep their sunlight going.
This gives you some idea, not only how dense they are, but the amazing difference between where they are and where they are not. So remember, all these guys are swimming, and as they swim, they’re turning slightly, simply to equally radiate the algae that are responsible for their survival. So this is a very, very tight symbiotic relationship, similar to what the corals have. But of course, these are free swimming jellyfish, so a very different sort of situation.

Last I heard, there were 27 million jellyfish living in a lake about the size of this building, maybe not quite the size of this building. But these are regular old jellies that have tentacles; they have stings. But they’ve evolved this funny relationship with an algae that works for both the algae and the jellies. And as a result, they’re able to do quite well.

These look just like the jellyfish that hunt for a living. They’ve got a mouth. They’ve got tentacles. They’ve got those oral arms. They just no longer use any of that. Their whole purpose in life if you want to think about it that way, is simply to keep that algae in the sunlight, because that’s the whole way that they manage to make a living. But again they don’t take anything in their mouth. I don’t think they probably ever take anything through there.

And if one gets close to anemones, it gest in real trouble, because the anemones grab it. And as it struggles, it generally gets caught by more and more anemones. And the fishes, of course, are hanging out trying to see if they can’t get just an extra bite or two. And, the anemones really can be almost pulled off their bases. But clearly they’ve evolved to hang onto these jellyfish, because that’s their root, and perhaps their own source of food in these lakes, although I don’t if that’s true or not, now that I think about it, certainly their major source of food.

But this system also provides food for much of the rest of the lake. Take a sponge, and beside the sponge, a snail. And these snails are attracted to the struggle, whether it’s the chemicals or whatever, of the jellies. And so the snails come when the jellies get caught. And they’ll finish off what the anemones don’t get. So the snails come up and finish off what the anemones don’t get. So the bottom’s a bad place if you are a Mastigias. But clearly, most of the Mastigias have learned how to avoid that particular problem because the lake has got millions and millions of jellies in it. And there’s maybe a 100 caught at the bottom at any one point in time.

As you go down in this lake though, the most striking thing happens. The water changes character. It gets slightly warmer. And as it gets warmer, suddenly there’s a whole new world. Different species of jellyfish. These are hunters, not farmers. They’ve got longer tentacles. These guys don’t have any symbiotic algae. They’re almost completely clear.

They have the same problem on the bottom however. If they get down here with these anemones, well, the anemones would just as soon eat an Aurelia as they would a Mastigias. At least, that seems to be the case because down on the bottom, you do find the Aurelia stuck to the anemones. Also, note that the bottom is full of sponges. So sponges and Cnidarians, and a few fish make up almost this entire ecosystem.

So while many places in the world, jellyfish blooms are looked upon with a good deal of disfavor, I have to tell you that many places when we fish, almost all of the food fish ; we get jellyfish instead, which isn’t something we necessarily would want. In the marine lakes of Palau, jellyfish have been there forever. It’s not a human artifact. And it’s really a marvelous ecosystem. If you like diving, going to Palau is a great thing. It turns out that’s the only thing there is to do in Palau, however. So I don’t recommend it unless you like to dive.

So, that is it for this lecture. Thank you!

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