Category: Marine invertebrates

Pugnacity, and the need to regrow limbs

Posted on by Allison J. Gong

My friend Peter Macht is the aquarium curator at the Seymour Marine Discovery Center. He is responsible for all of the live (i.e., wet) exhibits and has a team of student and volunteer aquarists who help him care for the animals in the hall and behind the scenes. Peter and I go way back together, to years before the Seymour Center opened in 2000. Back then the only public space at Long Marine Lab was called the Shed Aquarium because it was, literally, in a wooden shed. I do miss the marine lab the way it was then, when I knew everybody who was there and it was a quieter and more peaceful place to work. However, we’ve come a long way, baby, and the Seymour Center is in just about every way imaginable, a huge improvement over the Shed Aquarium.

For one thing, there are two large exhibits in the Seymour Center, each of which would occupy about half the volume of the old Shed Aquarium. One of these tanks, the Sandy Seafloor tank, has housed many different animals over the years: surf perches, sand dabs, sharks, rays, señoritas, and various invertebrates. My personal favorite continues to be the burrowing sea star Astropecten, although she hasn’t been on exhibit for several years now. The current inhabitants are a close second favorite, even though when they first arrived I didn’t expect them to be nearly as fascinating as I’ve found them.

Pleuroncodes planipes is a little red crab commonly called the pelagic crab or the tuna crab. For once the common names reveal something about the biology of the animal–these crabs spend their lives in the water column over the continental shelf, at least as youngsters, and are one of the favored food items of tunas. They are usually found in the waters of southern California and Mexico, but during the El Niño event of 2015 they washed onto the beaches around Monterey Bay in humongous numbers; they also did so during the ENSO event of 1982-1983.

Front view of a living pelagic crab, P. planipes. 22 November 2016 © Allison J. Gong
Front view of a living pelagic crab, P. planipes.
22 November 2016
© Allison J. Gong
Lateral view of a living pelagic crab, Pleuroncodes planipes. 22 November 2016 © Allison J. Gong
Lateral view of a living pelagic crab, Pleuroncodes planipes.
22 November 2016
© Allison J. Gong

Although they resemble crayfish, Pleuroncodes is a crab. They are anomuran crabs more closely related to hermit crabs and porcelain crabs than to “regular” brachyuran crabs such as shore crabs and rock crabs. The way you tell the difference between anomuran and brachyuran crabs is to count the number of thoracic walking legs, keeping in mind that the claws are included as walking legs: anomurans have four pairs while brachyurans have five pairs. You can see in the picture of the lateral view that this crab has three pairs of stick-like legs and one pair of chelipeds (claws).

Being arthropods, red crabs molt periodically. Peter has been collecting data on frequency of molts for individual crabs since the spring of 2016. Doing so requires isolating crabs in separate containers, to keep track of which crab molts when and also to prevent the crabs from ripping apart a freshly molted compadre, which they do with great enthusiasm. It is not unusual to see one or more of the inhabitants of the Sandy Seafloor tank missing a leg.

Here’s one of Peter’s tables containing crabs in baskets:

Individual red crabs (P. planipes) in separate baskets. 22 November 2016 © Allison J. Gong
Individual red crabs (P. planipes) in separate baskets, for their own safety.
22 November 2016
© Allison J. Gong

It’s just as well that these guys have extraordinary regenerative capabilities, as they are eager to rip each other’s legs off. With most crabs that I’ve observed in the lab limb regeneration is a gradual process, with the new leg growing a bit with each successive molt. Chelipeds, even with their increased size and complexity, seem to regrow faster than the other walking legs, likely reflecting their importance to the animal’s lifestyle.

Pelagic crab (P. planipes) and its molt. 22 November 2016 © Allison J. Gong
Pelagic crab (P. planipes) and its molt.
22 November 2016
© Allison J. Gong

Peter told me last week that he’d seen one of his isolated crabs regenerate an entire cheliped with a single molt, going from nothing to an almost-full-size functional limb essentially overnight. This seemed very unlikely to me, but Peter said he’d seen the before (the empty molt) and after (the actual crab) together in the same container. Unfortunately the crabs end up demolishing and eating their molts within a couple of days, so the evidence doesn’t stick around very long.

Sometimes, though, you get lucky. When I was at the lab yesterday morning Peter told me that he’d seen another of his crabs molt, and that it had grown a missing cheliped since the previous day. And this time he could show me the proof. Voilà!

A pelagic crab (P. planipes) with its molt. Note that the molt has only one cheliped, while the crab itself has two. 22 November 2016 © Allison J. Gong
A pelagic crab (P. planipes) with its molt. 
22 November 2016
© Allison J. Gong

Note that the molt has only one cheliped, the left, while the crab itself has two. How cool is that? The crab’s right cheliped is a bit smaller than the left, as might be expected of a regenerating limb, but it’s definitely intact and functional. It was pretty exciting to see evidence of wholescale limb regrowth taking place in such a short period of time, which must be incredibly energetically expensive. On the other hand, chelipeds are extremely important for defense, and there is obvious selective pressure to regrow them as quickly as possible should a crab be unfortunate enough to lose one.

Peter gave me permission to examine the molt more closely, so I took it back to the lab where the lighting is better. And surprise! The right cheliped apparently didn’t grow from nothing overnight. If you look really hard at the photo above, you can just barely see a ghostly transparent sheath where the missing arm would be. Hmm. This was not at all what I expected. Did I really see that?

It turns out that, yes, that is exactly what I saw.

Ventral view of the right side of a molt of the a pelagic crab (P. planipes).
22 November 2016
© Allison J. Gong

See that translucent tiny limb up front? That’s a little cheliped! And it had been there at least six months, as this crab’s last recorded molt was in April. Why hadn’t anyone seen it before? I think because this limb was so small that the crab kept it tucked underneath the carapace, where it wouldn’t be seen from the dorsal (top) side.

In the course of one morning I got taken for quite a roller coaster ride. Peter reminded me that he’d seen a crab apparently regrow a missing appendage in a single molt cycle . . . and had just found a crab whose molt showed exactly that . . . and then that molt ended up including a claw after all. What fun!

Now, why is that little claw so transparent? An arthropod’s exoskeleton is made of a material called chitin, with varying degrees of calcification depending on species. The large marine crustaceans (e.g., crabs and lobsters) have heavily calcified exoskeletons, while insects have much more lightweight, less-calcified exoskeletons. As a crab prepares to molt, one of the things its body does is resorb some of the minerals that it had deposited in the soon-to-be-discarded exoskeleton, so they can be re-used in the new one. If you find a discarded molt on the beach, pick it up and note how little it weighs; you’d be surprised at how flimsy it is.

Here’s my hypothesis. I think that this little cheliped, because it was newly regenerated before this most recent molt, was only lightly calcified. The crab may have used it, but it wouldn’t have been much use for defense. Then, the next time the crab molted the claw was shed along with the rest of the exoskeleton, and the limb was significantly larger. This crab now possesses a complete pair of chelipeds again. After examining the molt I returned it to the crab, which has probably torn it to pieces and eaten already. It’s a way for the animal to recover some of the nutrients it allocated into building the exoskeleton in the first place.

Kind of a neat trick, isn’t it?

Not-so-happy anniversary

Posted on by Allison J. Gong

Seeing as today is the third anniversary of the first blog post I wrote about sea star wasting syndrome (SSWS), I thought it would be appropriate to take inventory of my remaining stars and see how they’re doing. Right now I have custody of ~10 bat stars (Patiria miniata), 7 ochre stars (Pisaster ochraceus–collected last year for the juvenile survival experiment I did with Scott), and 1 Mediaster aequalis. For whatever reason the M. aequalis hasn’t been affected by SSWS so I’m going to disregard it for now. Of the 10 or so bat stars, four live in one of my seawater tables, roaming free-range in quite a large volume of water. The other half-dozen or so live in a tank in a different building. The Pisasters live in 1s and 2s in tanks distributed in two rooms in the same lab.

After the initial horror and shock of the spectacular onset of SSWS, in which we watched stars rip themselves into pieces right before our eyes, what we’ve seen has followed the standard epidemiology pattern. Any time a novel pathogen enters a population, the individuals that have no immunity or resistance are the first to die. The disease spreads rapidly through the population, wiping out all of these weaker individuals. However, not everyone dies. Even during the Black Death of the 14th century, the very fact that 1/3-1/2 of the human population died of bubonic plague means that 1/2-2/3 survived. Those survivors presumably had some degree of resistance to the disease.

At the same time three years ago that all of my forcipulate stars died, divers were noticing similar phenomena happening subtidally. It didn’t take long for us to realize that Something Big was going on, which was eventually dubbed SSWS. Fast-forward three years and now I’m seeing healthy, hand-sized P. ochraceus in the intertidal again. These individuals are certainly survivors from the SSWS outbreak; they were likely small juveniles during the plague, and were able to come out of hiding and expand into open niches after so many of the adults died. Whether or not natural populations will recover completely remains to be seen, but as of right now things look promising.

About a year ago, having gone two years without showing any signs of being sick, one of my bat stars developed lesions on its aboral surface. It’s the red star in the middle of that blog post. This star is one of the four that live in my shallow table. It has now been sick for a year. See how it has changed since then:

Patiria miniata (bat star) with small lesion. 4 September 2015 © Allison J. Gong
Patiria miniata (bat star) with small lesion.
4 September 2015
© Allison J. Gong

and

Patiria miniata with aboral lesions. 7 September 2016 © Allison J. Gong
Patiria miniata with aboral lesions.
7 September 2016
© Allison J. Gong

The lesions have all gotten worse–the largest is about 2 cm long now–and the body margin has some ripples that it didn’t have before, but the star is still alive. For a while it wasn’t eating, as far as I could tell, but two days ago I watched it eat a piece of fish. Perhaps the return of cooler water is helping this animal survive.

One of its tablemates, however, hasn’t been so lucky. I first noticed apparent SSWS damage in a second star several months ago. Today was the first chance I had to look closely at it.

Aboral view of Patiria miniata with damage to body wall. 7 September 2016 © Allison J. Gong
Aboral view of Patiria miniata with damage to body wall.
7 September 2016
© Allison J. Gong
Oral view of Patiria miniata with damage to body wall. 7 September 2016 © Allison J. Gong
Oral view of Patiria miniata with damage to body wall.
7 September 2016
© Allison J. Gong

The most noticeable injury to this star is that big interradial divot. It looks like someone took a bite out of the body at that spot. The margins of the wound are white and fluffy, similar in appearance to the lesions caused by SSWS.

For years now this star has had an abnormal spot on its aboral surface. I’ve been calling it a bubble, for lack of a better word. The bubble may be an over-inflated papulla (skin gill) and it didn’t seem to be causing any problems for the star. I’d touch it and it would deflate, then re-inflate almost immediately. When I touched it today, it shrank back a little but didn’t really deflate.

Strange "bubble" on aboral surface of P. miniata. 7 September 2016 © Allison J. Gong
Strange “bubble” on aboral surface of P. miniata.
7 September 2016
© Allison J. Gong

If you look really closely at the above photo, you can make out clusters of small, clear, clublike projections. These are papullae, extensions of the internal body lining that project through the skeletal ossicles to the outside and act as gas exchange surfaces. The bubble is many times larger than the normal papullae. Because it has been there for so long, years before the divot in the interradial margin, I don’t think the bubble is due to SSWS. I don’t even know if it’s a wound, or merely an overinflated papulla. The largest star in this table has also had a bubble for many years, but no lesions or wounds indicating SSWS or other disease.

So. Three years after the outbreak of SSWS I still have stars that are sick. They’ve been sick for a long time and aren’t getting worse very quickly, from which I conclude they may eventually recover. At the very least they must have some resistance to the SSWS pathogen because they’ve managed to survive so far. One more thing. Way back in 2013 when all of the forcipulates were tearing themselves into pieces and melting into piles of goo, these bat stars were among them, scavenging on the dead and decaying tissue. For a while I feared that eating contaminated tissue might cause the disease, but that doesn’t seem to be the case, as these two didn’t get sick until two years after the initial exposure.

I hope these two stars make it. Cooler water temperatures should help. When they’re really sick they stop eating (they haven’t eaten much in the past year) but if they’re going to eat now I’ll keep feeding them. Fingers crossed!

The original clone wars

Posted on by Allison J. Gong

A long time ago in a galaxy called the Milky Way, a great adventure took place. We don’t know exactly when it happened, but it must have been very shortly after the evolution of the first cells. Some small prokaryotic cell walled itself off from its surroundings. Then it learned how to replicate itself and as cells continued to divide they began interacting with clones of themselves. Sooner or later, however, our clone of cells encountered cells from a different genetic lineage. These foreign cells were “other” and were recognized as such because they had a different set of markers on their outer covering. Perhaps there was an antagonistic interaction between the two clones of cells. In any case, this ability to distinguish between “self” and “non-self” was a crucial step in the evolution of life on Planet Earth.

The entire immune system in vertebrates is based on self/non-self recognition. It is why, for example, transplanted organs can be rejected by their new host–the host’s immune system detects the transplanted tissue as “non-self” and attacks it. As a result, patients who receive donor organs usually take immune-suppressing drugs for some period of time after the transplant.

The vertebrate immune system is quite complex and very interesting. It has two main components: (1) cell-mediated immunity, in which the major players are T cells; and (2) humoral (i.e. blood-based) immunity, which is the part of the immune system that produces antibodies to a pathogen when you get a vaccination. However, even animals much less structurally complex than vertebrates have some ability to recognize self from non-self.

Sponges, for example, exist as aggregations of cells rather than bodies with discrete tissues and organs. Most zoologists, myself included, consider sponges to be among the most ancient animal forms. They have different types of cells, many of which retain the ability to move around the body and change from one type to another; this totipotency is a feature that sponge cells share with the stem cells of vertebrates. There are sponges that you can push through a mesh and disarticulate into individual cells, and then watch as the cells re-aggregate into an intact, functioning body. As if that weren’t cool enough, if you take two different sponges and mush them into a common slurry, the cells from the distinct lineages re-aggregate with cells to which they are genetically identical. So even animals as primitive as sponges have some degree of self/non-self recognition.

If you’re lucky, you can see self/non-self recognition and aggression in the intertidal. Here in northern California we have four species of sea anemones in the genus Anthopleura:

  • Anthopleura xanthogrammica, the giant green anemone
  • Anthopleura sola, the sunburst anemone
  • Anthopleura elegantissima, the cloning anemone
  • Anthopleura artemisia, the moonglow anemone (and my favorite)

Of these species, only A. elegantissima clones. It does so by binary fission, which means that the animals rip themselves in half.

Sea anemone (Anthopleura elegantissima) undergoing binary fission in a tidepool at Davenport Landing. 9 April 2016 © Allison J. Gong
Sea anemone (Anthopleura elegantissima) undergoing binary fission in a tidepool at Davenport Landing.
9 April 2016
© Allison J. Gong

It looks painful, doesn’t it? As the two halves of the animal walk in opposite directions they pull apart until the tissue joining them stretches and eventually rips. Then each half heals the wound and carries on as if nothing had happened. Each anemone is now a physiologically and ecologically independent animal, and can go on to divide itself. And so on ad infinitum. The logical consequence of all this replication is a clone of genetically identical anemones spreading over a rocky surface. And that’s exactly what you get:

Clones of the sea anemone Anthopleura elegantissima, emersed on a rock at Monastery Beach. 27 November 2015 © Allison J. Gong
Clones of the sea anemone Anthopleura elegantissima, emersed on a rock at Monastery Beach.
27 November 2015
© Allison J. Gong

Okay, it’s hard to tell that these are sea anemones, but this is what they look like when the tide goes out and leaves them emersed. They pull in their tentacles, close off the oral disc, and cover themselves with sand grains. They look like sand but feel squishy and will squirt water if you step on them. In this photo, each anemone is probably 4-5 cm in diameter.

There are three patches of anemones in the photo above, separated by narrow strips of real estate where there are no anemones. Each patch is a clone, essentially a single genotype divided amongst many individual bodies. The anemones in each clone pack tightly together because they are all “self.” However, they recognize the anemones of an adjacent patch as “non-self” and they won’t tolerate the intrusion of neighbors onto their territory. Those strips of unoccupied (by anemones) rock are demilitarized zones. When the rock is submerged the anemones along the edges of the clones reach out their tentacles and sting their non-self neighbors. This mutual aggression maintains the DMZ and nobody gets to live there.

Because A. elegantissima lives relatively high in the intertidal the clonal patches are usually emersed when I go out to the tidepools. Its congener, A. sola, lives lower in the intertidal and is more often immersed at low tide. Anthopleura sola is larger than A. elegantissima and is aclonal, meaning that it does not divide. Anthopleura sola also displays quite dramatically what happens when anemones fight.

These two anemones, each about 12 cm in diameter, were living side-by-side in a tidepool. You can see that each animal has two kinds of tentacles: (1) the normal filiform feeding tentacles surrounding the oral disc; and (2) thicker, whitish club-shaped tentacles below the ring of feeding tentacles. These club-shaped tentacles are called acrorhagi, and are used only for fighting. The acrorhagi and the feeding tentacles may contain different types of stinging cells, reflecting their different functions. All tentacles are definitely not the same.

Anthopleura sola anemones fighting in a tidepool at Davenport Landing. 8 May 2016 © Allison J. Gong
Anthopleura sola anemones fighting in a tidepool at Davenport Landing.
8 May 2016
© Allison J. Gong

These animals, which represent different genotypes, are non-self to each other, so they fight. They inflate their acrorhagi, move their feeding tentacles out of the way, and reach across to sting each other. See how some of the acrorhagi on the animal on the right don’t have nice smooth tips? Those tips have been lost during battle with the animal on the left; the tips are torn off and remain behind to continue stinging the offender even after the tentacle itself has been withdrawn.

Here’s another picture of the same two anemones, taken from a different angle:

Anthopleura sola anemones fighting in a tidepool at Davenport Landing. 8 May 2016 © Allison J. Gong
Anthopleura sola anemones fighting in a tidepool at Davenport Landing.
8 May 2016
© Allison J. Gong

The goal of these fights is not to kill, but to drive the other away so that each anemone has its own space. Eventually one of them will retreat, and a more peaceful coexistence will be established. Fights like these have been going on for over half a billion years. Eat your heart out, George Lucas.

How can you eat sand?

Posted on by Allison J. Gong

Well, we can’t—at least, not very well. I suppose we can eat it in small amounts, but sand itself is one of the most nutrient-poor substances imaginable. Sand is, after all, ground up bits of rock. It would provide certain minerals, depending on the type of rock, but none of the essential macronutrients—carbohydrates, proteins, and lipids—that animals need to survive.

When I was a kid I thought that sand dollars were called sand dollars because I’d find their broken tests on sandy beaches. I knew they lived in sand, hence the name. As I started studying marine invertebrates in college I learned that sand dollars don’t just live in the sand; they also eat sand. In addition to organic matter, usually in the form of detritus, sand dollars eat sand to create ballast. This makes them heavy and keeps them from being picked up and carried away by waves. It is also why, if you come across an intact sand dollars test and break it open, sand will fall out of it.

I have a batch of recently settled Dendraster excentricus, the common sand dollar in northern California. They began metamorphosing only 30 days post-fertilization. As the larvae settled and transformed into tiny sand dollars, I decided to try to figure out what to feed them. These animals aren’t grown commercially and there doesn’t seem to be a definitive answer on how to raise them. One of the suggestions I got was “Well, we know they eat sand, so feed them sand.”

Which is what I did. The first time I just sprinkled a bit of sand in the dish with the juvenile sand dollars. Then I looked under the microscope to see that the sand grains were about 10 times the size of the animals. Oops. But the sand dollars didn’t look unhappy so I let them be. I decided that they also needed something organic to eat so I ground up a small piece of Ulva and dropped some of the resulting slurry on them.

The second time I offered sand to the sand dollars I ground it up in a mortar and pestle that I scrounged from the lab next door. Let me tell you, grinding sand makes a sound that is every bit as horrible as you imagine. At least it produced smaller particles that the sand dollars might be able to eat. I continued to offer Ulva mush in addition to the fine sand. If they end up eating either sand or Ulva, I can provide that pretty easily. The question is, how do I know whether or not they’re eating?

Juvenile sand dollars (Dendraster excentricus). 13 May 2016 © Allison J. Gong
Juvenile sand dollars (Dendraster excentricus).
13 May 2016
© Allison J. Gong

How many sand dollars can you find in the above photo? They are exactly the same color as the sand. I don’t have real proof that these little guys are eating sand; even their poops would look like the sand. The animals do tend to clear the space in their immediate vicinity, but I think that might be due to the action of the tube feet and spines rather than consumption of either sand or Ulva. In this video clip you will see that the sand dollars are very active, even though all the motion doesn’t seem directed the way it does in urchins at this stage.

They do a lot of waving around, but don’t actually walk. They do, however, seem to like being tilted up a bit, similar to the way adult sand dollars position themselves when in calm water:

By Chan siuman at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=23041434
By Chan siuman at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=23041434

I do have circumstantial evidence that my sand dollars are eating something. The first ones metamorphosed at 30 days post-fertilization. Today is day 51 post-fertilization, which means some of the animals have been post-larvae almost as long as they were larvae. I know it takes about a week for newly metamorphosed sea urchins to form their new guts and begin feeding, and I assume it’s the same for sand dollars. In fact, because these sand dollars raced through larval development so quickly I expected their juvenile mouths to break through quickly as well. If this were the case, then these animals should have had complete and functional guts for almost two weeks now. The fact that they’re not dead or dying makes me think that they have to be eating.

Call it a hunch, call it intuition, call it wishful thinking. I’m not sure how they’re doing it, but I think they’re fine. Next week I hope I can find time to measure them.

Not always a death sentence

Posted on by Allison J. Gong

I’ve already written several times about seastar wasting syndrome (SSWS) and you’ve probably seen your share of photos of wasted, melting, self-mutilating stars. However, you may also be wondering about the current state of affairs regarding SSWS, and whether or not sea star populations have recovered at all since the outbreak began three years ago now. The question “How does SSWS affect the stars?” can be addressed on two different levels: the level of an individual star, and the level of the population of stars. In this post I discuss the first aspect, and in a subsequent post I’ll share my observations of sea star populations in the field.

Level 1: SSWS as it affects individual stars

I remember very vividly the feeling I had when I opened the door to the wet lab and glanced into my table to see this:

Large Patiria miniata (bat star) scavenging on dead Pisaster ochraceus (ochre star)
Large Patiria miniata (bat star) scavenging on dead Pisaster ochraceus (ochre star) in my seawater table at Long Marine Lab.
4 September 2013
© Allison J. Gong

And after that it only got worse, until (almost) every star was dead. It was interesting to watch how the disease manifests in different species of stars, though. The forcipulates–genera Pisaster (ochre stars), Pycnopodia (the huge sunflower star), Orthasterias (rainbow star)–succumbed quickly and violently. These were the animals that ripped their own arms off, often without showing any prior signs of distress, and then melted away.

Pisaster giganteus star melting from wasting disease. ©2013 Allison J. Gong
Pisaster giganteus star disintegrating due to wasting disease.
September 2013
©2013 Allison J. Gong

On the other hand, other species seemed to be more resistant to SSWS. At least, they didn’t succumb right away. Perhaps the disease (if it is indeed a disease) progresses more slowly in some groups of species compared to others. These stars, including the bat stars (Patiria miniata) and leather stars (Dermasterias imbricata), didn’t rip their arms off. The only leather star in my care died about a week after the forcipulates bit the dust, and the bat stars seemed fine for months. And when these species got sick they showed different symptoms.

Instead of self-mutilation, the leather and bat stars developed lesions on their skin. The lesions could be very deep, exposing the animal’s internal organs (guts and gonads) to the external environment.

Bat star (Patiria miniata) showing severe symptoms of wasting syndrome. 16 March 2015 © Allison J. Gong
Bat star (Patiria miniata) showing severe symptoms of wasting syndrome.
16 March 2015
© Allison J. Gong

The white objects inside the yellow circle are the star’s skeletal ossicles, which have fallen away because the tissue holding them in place has been severely eroded. I haven’t seen a leather star survive longer than a week once the lesions appear. Bat stars, on the other hand, can and do live for months with lesions. For example, this star of mine first developed lesions back in September 2015:

Patiria miniata (bat star) with small lesion. 4 September 2015 © Allison J. Gong
Patiria miniata (bat star) with small lesion.
4 September 2015
© Allison J. Gong

The lesions were small and superficial, and for a long time the animal didn’t actually seem sick. It wandered around its table, remained sticky, and even ate. Now, seven months later, the star is still hanging in there. I took this photo of it yesterday:

Bat star (Patiria miniata) with symptoms of SSWS. 4 May 2016 © Allison J. Gong
Bat star (Patiria miniata) with symptoms of SSWS.
4 May 2016
© Allison J. Gong

The lesion is bigger and deeper and now the innards are exposed. The star is also a little deflated, which might be a bad sign. From what I’ve observed, once an animal can no longer maintain its internal turgor pressure, it probably can’t recover. However, this one isn’t totally deflated yet, so I still have hope for it. Heck, this animal has been sick for over half a year now and hasn’t died yet. It obviously has some ability to resist the illness, or perhaps it’s just dying very slowly.

Just for kicks I zoomed in on the lesion under the dissecting scope, and it actually looks sort of cool. It isn’t every day that you can see the internal structures of an animal without cutting it open.

Lesion on aboral surface of Patiria miniata. 4 May 2016 © Allison J. Gong
Lesion on aboral surface of Patiria miniata.
4 May 2016
© Allison J. Gong

Sea stars don’t have a lot of space in the central disc of the body, so they keep their gonads and guts in their arms. Each arm contains a pair of pyloric caeca (extensions of the gut) and a pair of gonads. In the photo above, the whitish ribbons are the pyloric caeca and the tan bits are gonad. Just for kicks I snipped off a piece of the gonad and looked at it under the compound scope. And lo and behold, it’s a girl!

Female gonad of a wasting Patiria miniata. 4 May 2016 © Allison J. Gong
Female gonad of a wasting Patiria miniata.
4 May 2016
© Allison J. Gong

Those large round-ish blobs are oocytes in varying stages of maturity. I’m a little surprised to see any developing oocytes at all, given that this poor star has been sick for so long. Maybe this is a good sign. The internal fluid of the animal’s main body cavity is essentially seawater, so having the gonads and guts exposed to the outside might not be the direct avenue to infection that it would be for us. From what I can tell the tissue itself looks healthy: it doesn’t appear to be decomposing, the oocytes are full and more or less round, and there aren’t a lot of ciliates swarming all over it. So I think there’s hope for this animal, which has already survived so much, to pull through.

Another bat star that I’ve been keeping an eye on is a beautiful 8-armed star that was collected by Prof. John Pearse. Somehow I never managed to take a picture of this animal until it got sick about two weeks ago. One of the lab assistants noticed that it looked a little off on a Saturday, and two days later it had some nasty lesions.

8-armed Patiria miniata with lesions characteristic of SSWS. 23 April 2016 © Allison J. Gong
8-armed Patiria miniata with lesions characteristic of SSWS.
23 April 2016
© Allison J. Gong
Close-up of lesion on 8-armed P. miniata. 23 April 2016 © Allison J. Gong
Close-up of lesion on 8-armed P. miniata.
23 April 2016
© Allison J. Gong

Because this bat star went from zero symptoms to ulcerated lesions in two days, we didn’t think it would last much longer. The lab assistants isolated it in a tub filled with 0.2-µm filtered seawater and have been changing its water daily. Just as it didn’t take long for symptoms to appear, it didn’t take long for this individual to show signs of recovery. About five days after first being isolated the star was sticking to the side of its tub, indicating that its water vascular system was still functioning. A week after that, I looked at it again and saw that the lesions seemed to be healing!

8-armed P. miniata with healing aboral lesions. 4 May 2016 © Allison J. Gong
8-armed P. miniata with healing aboral lesions.
4 May 2016
© Allison J. Gong
Apparently healing lesion on 8-armed P. miniata. 4 May 2016 © Allison J. Gong
Close-up of apparently healing lesion on 8-armed P. miniata.
4 May 2016
© Allison J. Gong

The surface of the lesion appears to be more solid, as if the epidermis had been knitted back together. There’s still a bit of gonad exposed, though. Is this significant? At this point I’m not sure. The animal will remain in ICU, separated from all other echinoderms, until we are absolutely certain that it has recovered. And of course I may be jumping the gun to say that the animal is recovering at all. Only time will tell. It is, however, extremely refreshing even to think about SSWS without despair, for which I am grateful.

Seeing stars at Pigeon Point

Posted on by Allison J. Gong

This morning I drove up the coast to Pigeon Point. It was cold and very windy, and I was grateful to have decided to wear all of my layers. I don’t remember any cold mornings from last year’s low tides, which made me think that perhaps we’re returning to a more normal non-El Niño weather pattern. The wind was screaming down the coast from the north, and if it keeps up we should get some upwelling in a few days. Fingers crossed!

Even the pelicans, which can fly through strong winter storms, were having a bit of trouble with the wind:

Pelicans in flight over turbulent seas at Pigeon Point. 24 April 2016 © Allison J. Gong
Pelicans in flight over turbulent seas at Pigeon Point.
24 April 2016
© Allison J. Gong

My favorite kelp grows in the intertidal, and it wasn’t having any difficulty at all with the strong surf. It’s not large and doesn’t form the magestic kelp forests that divers flock to, but it is very charming in its own way. The sea palm Postelsia palmaeformis is a small  (1/3-1/2 meter tall) kelp that lives only on exposed rocks sticking out into the brunt of the waves. It requires the full force of the crashing waves, where other algae would get broken off. They have a thick flexible stipe that bends with the waves and then pops back up. Postelsia is a protected organism and I can’t collect it even with my scientific collecting permit, which is fine with me.

Postelsia palmaeformis on exposed outer coast at Pigeon Point 24 April 2016 © Allison J. Gong
Postelsia palmaeformis on exposed outer coast at Pigeon Point
24 April 2016
© Allison J. Gong

This is the kind of environment in which Postelsia thrives:

You can tell how windy it was by the sound of the wind and my inability to hold the camera steady. As the tide comes in the pounding from the waves will only get worse. These little algae are pretty damn impressive!

Pigeon Point has always been a good place to see the 6-armed stars of the genus Leptasterias. Unlike the five arms that most of the local asteroids have, Leptasterias has six. And unfortunately for us naturalists, the taxonomy of the genus is incompletely understood. All that is agreed upon is that there are several species in the genus. This is referred to as a species complex, acknowledging that the genus contains more than one species but that the species have yet to be definitively described.

Leptasterias sp. at Pigeon Point. 24 April 2016 © Allison J. Gong
Leptasterias sp. at Pigeon Point.
24 April 2016
© Allison J. Gong
Leptasterias sp. at Pigeon Point. 24 April 2016 © Allison J. Gong
Leptasterias sp. at Pigeon Point.
24 April 2016
© Allison J. Gong
Leptasterias sp. at Pigeon Point. 24 April 2016 © Allison J. Gong
Leptasterias sp. at Pigeon Point.
24 April 2016
© Allison J. Gong
Leptasterias sp. at Pigeon Point. 24 April 2016 © Allison J. Gong
Leptasterias sp. at Pigeon Point.
24 April 2016
© Allison J. Gong

As you can see, these stars vary quite a bit in terms of arm thickness and color pattern. Most of the time they are blotchy but the blotches can be pink, gray, orange, or cream-colored. Some of the stars have slender arms with very little taper, while others have thicker arms that taper strongly to the tips. For the time being, until the sea star systematists come to consensus about the species in this genus, I’ll refer to all of them as Leptasterias sp.

Most of the Leptasterias that I see in the field are in the size range of 1-4 cm in diameter, usually no longer than my thumb. Today I saw a big one, which would have been about the size of the palm of my hand.

Leptasterias sp. at Pigeon Point. 24 April 2016 © Allison J. Gong
Leptasterias sp. at Pigeon Point.
24 April 2016
© Allison J. Gong

The reason this star doesn’t look quite as big as that in the above photo is that it was eating when I disturbed it. The star was humped up over its breakfast!

Leptasterias sp. at Pigeon Point 24 April 2016 © Allison J. Gong
Leptasterias sp. at Pigeon Point
24 April 2016
© Allison J. Gong

The unfortunate breakfast item, the turban snail Tegula funebralis, was about 2 cm in diameter. It seems like a very large and well-protected prey item for a star this size, doesn’t it? And yet, there it is. The animal is always right, and Leptasterias certainly knows what it should be eating.

And lastly, because they were just so beautiful and I can’t help myself, I’m going to close with photos of anemones.

Anthopleura sola at Pigeon Point 24 April 2016 © Allison J. Gong
Anthopleura sola at Pigeon Point, surrounded by encrusting and upright coralline algae
24 April 2016
© Allison J. Gong
Anthopleura xanthogrammica at Pigeon Point 24 April 2016 © Allison J. Gong
Anthopleura xanthogrammica at Pigeon Point
24 April 2016
© Allison J. Gong
Anthopleura sola at Pigeon Point 24 April 2016 © Allison J. Gong
Anthopleura sola at Pigeon Point
24 April 2016
© Allison J. Gong

Take that, charismatic megafauna!

A little less confounded now

Posted on by Allison J. Gong

So. Last week when I looked at my sand dollar larvae I wasn’t at all sure what to make of them. I thought that all of the offspring from one of the matings (F2xM1) were going south and didn’t know how much longer they would survive. The offspring from the other two matings seemed to be doing much better.

Fast forward a week and a half and my, how things have changed. I have some juvenile sand dollars now! And so far they are all from the F2xM1 mating, the ones that had started looking strange and that I thought might die. I’m surprised that any of the larvae metamorphosed, as my general understanding of sand dollars was that competent larvae settle among adults of their species, so that when they finish metamorphosis they would be in a suitable location to grow up. However, the animals is always right, and in this case I was happy to learn that my understanding was wrong.

This larva is almost competent. The main part of its body is almost completely filled by the juvenile rudiment (the tannish structure on the left side of the more reddish stomach) and the arms are shorter.

Almost-competent pluteus larva of Dendraster excentricus, age 30 days. 22 April 2016 © Allison J. Gong
Almost-competent pluteus larva of Dendraster excentricus, age 30 days.
22 April 2016
© Allison J. Gong

And here is a video of a trio of competent larvae.

Their bodies are almost entirely opaque now but they are unquestionably pluteus larvae.

As metamorphosis begins, the tube feet in the juvenile rudiment rupture through the body wall and the animal starts sticking to a hard surface, in this case a glass slide. For a while the animal is suspended between the larval and juvenile forms, in a state I call a larvenile. Hopefully the time spent in the larvenile stage is short, as to be neither larva nor juvenile is a bad thing. I’ve seen both sea urchins and sea stars get stuck in the larvenile stage, and they all died.

Larveniles are strange things. See for yourself.

In this video the right side of the animal (not the anatomical right but the right side of the image as it is presented on the screen) is the juvenile, and the left side is the larva. The larva half still has its fenestrated arm rods, which will eventually be dropped and left behind. It also retains for the time being the ciliated band which it used both to swim and to capture food. Another weird feature of the larvenile is the transition between the bilateral symmetry of the larva and the pentaradial symmetry of the juvenile. The bilateral symmetry has been more or less obliterated by the process of metamorphosis, but there isn’t enough of the juvenile to have complete pentaradial symmetry yet.

And, finally, metamorphosis is complete and a little sand dollar walks around on tube feet.

Yesterday this animal was a larva, and today it’s a juvenile. The sea urchins do the same thing. But these sand dollars have done everything faster than the urchins, and that includes development immediately after metamorphosis. You may recall that the purple urchins have only five tube feet when they metamorphose, and they struggle to coordinate them to walk. From what I can see these sand dollars have at least twice that many tube feet very shortly after metamorphosis, and they can walk much more quickly.

The tube feet themselves are different, too. Urchins’ tube feet are suckered and look like little plungers. Sand dollars’ tube feet have those pincher-looking tips (although I haven’t seen them open up and grab things yet). Adult sand dollars live partly buried in sand and don’t use their tube feet to cling to surfaces; they do use their tube feet to grab food, though.

Speaking of food, I don’t know what these juvenile sand dollars will be able to eat. Fortunately I have a while to figure out what to try feeding them, as their mouths won’t open up for at least a week (I hope). While it’s easy to observe what happens on the surface of the animal as it metamorphoses, it’s impossible to see what’s going on with the internal reorganization of the body. I do know that an entire new gut will have to be formed before the animal can eat. In the meantime it will have to survive on energy stores stashed in all that opaque part of the body.

Stay tuned!

Confounded

Posted on by Allison J. Gong

Remember that one batch of sand dollar larvae that were looking weird on Monday? Well, they still look weird. In fact, all of the larvae looked the same yesterday as they did on Monday, which seems strange, considering how quickly they galloped through development for the first three weeks of larval life. It’s as though they’ve entered some stasis period during which developmental progress slows way down. Or maybe I just can’t see the signs of change.

Pluteus larva of Dendraster excentricus, age 23 days. 15 April 2016 © Allison J. Gong
Pluteus larva of Dendraster excentricus, age 23 days. Mating: F2xM1. Diet: Rhodomonas only
15 April 2016
© Allison J. Gong

If I had seen these larvae for the very first time yesterday, I might not suspect that anything was strange. But having watched them twice weekly since fertilization and knowing how different they looked a week ago, my Potential Weirdness-o-Meter™ is redlining. These larvae have definitely changed in a week, and not in the way that I’m used to echinoid larvae developing. With their much shorter arms and overall stunted appearance, these guys appear to be regressing. However, they aren’t dying and they don’t really look bad. As I said on Monday, they just look . . . weird.

Remember how I said I’d split this cohort of larvae into two batches and fed them different things? At first I thought this strange appearance was due to the change in diet from a Rhodomonas/Dunaliella mixture to Rhodomonas only. The larva in the photo above was from the Rhodomonas-only jar, and perhaps its odd appearance could be explained by some deficiency in the monoculture diet. Then I continued on my rounds and looked at the larvae from the same mating that were still on the Rhodo/Dun diet.

Pluteus larva of D. excentricus, age 23 days. 15 April 2016 © Allison J. Gong
Pluteus larva of D. excentricus, age 23 days. Mating: F2xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong
Pluteus larvae of D. excentricus, age 23 days. 15 April 2016 © Allison J. Gong
Pluteus larvae of D. excentricus, age 23 days. Mating: F2xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong

All the larvae in these photos remained on the mixed diet, and they look pretty much the same as their siblings eating the monoculture diet. So I don’t think the change in diet explains the appearance of the larvae.

Okay, then. If it’s not the food that accounts for what these larvae look like, maybe it’s something about the mating itself. These larvae, from both food treatments, are all full siblings from one mother mated with one father. As full sibs they share, on average, 1/4 of their DNA with each other, which could account for the similarity in their appearances. Perhaps this “strange” look is due more to genetics than to the environment (i.e., food).

I can test this hypothesis by examining larvae from the other crosses. Rather fortuitously, as it turns out, when I spawned the adult sand dollars a little over three weeks ago now, only one male contributed enough sperm for me to use. Three females spawned usable amounts of eggs, so I set up three matings:

  • F1xM1
  • F2xM1
  • F3xM1

The female designated F2 gave the most eggs, and her offspring are the ones that I split into the Rhodo-only and Rhodo/Dun diets. Note that all of the larvae in this little experiment have the same father. This gives me the opportunity to test for maternal effects on development; in other words, having controlled for the effects of different fathers–ha! I make it sound as though I did that on purpose–I can now assume that differences (in growth rate, survivability, and successful metamorphosis if we get that far) between the different matings are at least partially due to differences in egg quality among the three mothers. Or to differing gamete compatibilities between each female and the one male.

So now let’s take a look at the larvae from other matings. We’ll start with F1xM1:

Pluteus larva of D. excentricus, age 23 days. Mating: F1xM1. Diet: Rhodomonas/Dunaliella mix. 15 April 2016 © Allison J. Gong
Pluteus larva of D. excentricus, age 23 days. Mating: F1xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong

This larva looks normal to me, or at least what I’ve come to assume is normal. And wow, that was one filthy cover slip,wasn’t it?

The offspring of the F3xM1 mating look very much the same:

Pluteus larva of D. excentricus, age 23 days. Mating: F3xM1. Diet: Rhodomonas/Dunaliella mixture. 15 April 2016 © Allison J. Gong
Pluteus larva of D. excentricus, age 23 days. Mating: F3xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong
Pluteus larvae of D. excentricus, age 23 days. Mating: F3xM1. Diet: Rhodomonas/Dunaliella mixture. 15 April 2016 © Allison J. Gong
Pluteus larvae of D. excentricus, age 23 days. Mating: F3xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong

And here’s a short video of that same pair of larvae. They look like they’re singing a duet. If I were the clever sort I’d dub in some music; alas, I’m not that clever. Does somebody want to do this for me?

What are they up to?

Posted on by Allison J. Gong

These sand dollar (Dendraster excentricus) larvae that I’ve been raising will be 21 days old tomorrow, and they are still on the fast track. They’re developing much more quickly than any of the sea urchin cohorts I have raised. Some of them already have juvenile rudiments with tube feet visible. With the urchins (Strongylocentrotus purpuratus) this is the age when I worry about the cultures crashing for no apparent reason, and so far these sand dollar plutei look great. I hope I didn’t jinx them by writing that. In any case, the sand dollars are known to go through larval development more quickly than their sea urchin cousins, so my larvae appear to be playing by the book, at least as far as timelines go.

Just for kicks I took the largest full-sib cohort I had and split it into two batches. One batch I’m feeding the recommended combination of Rhodomonas sp. (red) and Dunaliella tertiolecta (green), and the other I’m feeding Rhodomonas sp. only. I’ve been able to raise urchin larvae through metamorphosis on a diet of Rhodomonas so I assumed that this food might work for the sand dollars as well. It turns out, however, that the Rhodomonas-fed larvae look a little strange now.

Pluteus larvae of Dendraster excentricus, age 19 days. 11 April 2016 © Allison J. Gong
Pluteus larvae of Dendraster excentricus, age 19 days.
11 April 2016
© Allison J. Gong

Their bodies have become more opaque and compact; they’ve shrunk to a length of 450-500 µm. I wonder if this is the first stage in metamorphosis. I didn’t see a well-defined juvenile rudiment in any of the larvae I examined but that doesn’t mean it isn’t there. And although they look weird and deformed, they don’t necessarily look bad. They just don’t look . . . right.

On the other hand, there may indeed be something wonky going on. I have a jar of siblings of these larvae being fed a red/green diet, and they look totally different.

Pluteus larvae of Dendraster excentricus, age 19 days. 11 April 2016 © Allison J. Gong
Pluteus larva of D. excentricus, age 19 days.
11 April 2016
© Allison J. Gong

This is a beautiful 8-armed pluteus larva. It looks great! The arms are nice and long but none of the arm spines are poking through the ends. They appear to be eating well and have grown to a length of 700-800 µm. This is a ventral view, and that oblong blob on the left side of the pigmented stomach is the juvenile rudiment.

Here’s a close-up view of the rudiment:

Pluteus larvae of Dendraster excentricus, age 19 days. 11 April 2016 © Allison J. Gong
Pluteus larvae of D. excentricus, age 19 days.
11 April 2016
© Allison J. Gong

See how the rudiment is crowding into the stomach? And if you squint you might be able to talk yourself into seeing a couple of round blobs in the rudiment. These would be tube feet, which I can see as I focus the microscope up and down through the animal’s body but which don’t show up very well in a photograph.

The next day that I change the water and have a chance to look at these guys under the microscope is Friday. It’s only three days from now, but given how quickly the larvae are developing, a lot could happen between now and then. I’m a little nervous.

Sexy time for sea anemones

Posted on by Allison J. Gong

This morning I went out on the first morning low tide of the season. I was so excited to have the morning lows back that I got to the site early and had to wait for the sun to come up. Awesome thing #1 about early morning low tides: Having the intertidal to myself.

Dawn over Davenport Landing. 9 April 2016 © Allison J. Gong
Dawn over Davenport Landing.
9 April 2016
© Allison J. Gong

The purpose for the trip was to collect some algae for a talk I’m preparing; I’ll be speaking to the docents at Natural Bridges State Beach at their monthly meeting this coming Wednesday. They invited me to talk to them about algae. I already have a lecture on algae prepared, but last year I set the bar pretty high with this particular audience and want do something a little different. So I’ll talk to them for a bit, show them some of my pressings, and invite them to press a couple of specimens. This morning I collected a few pieces of algae and took a bunch of pictures.

The Anthopleura anemones continue to fascinate me. At Davenport Landing there’s an area where the rock has eroded and forms a sort of channel. In this channel at low tide the water comes about up to my knees. The rock in the channel remains clear of algae but sometimes contains sand. Scattered over the bottom of this channel are several A. artemisia anemones, which can burrow into the sand when it is present. I’ve photographed these animals many times, as they are magnificently photogenic and in deep enough water that I can just stick my camera below the surface and click away.

This morning the first anemone I looked at in this channel had some orange gunk on its oral surface. At first I thought it had latched onto a piece of bleached algae, but then noticed that others had the same thing. My second thought was, “Ooh, eggs!” If I were at the lab I’d have sucked up some of the gunk and examined it under the microscope.

Spawning female Anthopleura artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning female Anthopleura artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong

Usually when animals spawn the gametes are quickly dispersed by water currents. But this channel is high enough that at low tide it doesn’t exchange water with the ocean so there are no currents except those generated by the wind. Awesome thing #2 about early morning low tides: No wind. Once I used the camera as a sort of underwater microscope I could see the granular texture of the orange gunk, which told me that these were, indeed, eggs. Cool! Because I was on a hunt for algae I didn’t spend a lot of time censusing these anemones, but I figured that statistically speaking they couldn’t all be females. And sure enough, after a very short search I found some males.

Spawning male A. artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning male A. artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong
Spawning male A. artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning male A. artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong

So today I learned that April is when the A. artemisia anemones have sex. Makes sense, as spring is the time of year when many organisms (algae and invertebrates) in the intertidal reproduce. Reproduce sexually, that is.

Some animals reproduce clonally as well as sexually, and while sexual reproduction tends to be seasonal, clonal reproduction doesn’t seem to be. Along the coast of central/northern California we have four species of anemones in the genus Anthopleura:

  • A. artemisia, the moonglow anemone (see above)
  • A. elegantissima, the aggregating anemone
  • A. sola, the sunburst anemone
  • A. xanthogrammica, the giant green anemone

Of these four species, only A. elegantissima clones readily. It does this by ripping its body in half in a process called binary fission. The two halves of the animal pull away from each other and the tissue between them gets stretched thinner and thinner until it rips. Then each former-half heals the wound and gets on with life, completely independent of the other. It sounds rather awful but is a very effective way to form clones of genetically identical units that can monopolize large areas in the intertidal.

Anemone (Anthopleura elegantissima) undergoing binary fission, at Davenport Landing. 9 April 2016 © Allison J. Gong
Anemone (Anthopleura elegantissima) undergoing binary fission, at Davenport Landing.
9 April 2016
© Allison J. Gong

It’ll probably take this anemone another day or two to completely tear itself into two pieces. Anemones can continue to clone like this, with each individual splitting into a pair of individuals, for a long time. Eventually this process can form large clones. More about the ecology of these clones in a separate post some time.