Category: Marine invertebrates

You are what you eat, part the second

Posted on by Allison J. Gong

Two months ago now I gave my juvenile sea urchins a job. It’s the kind of job they’re perfectly suited for:  eating algae. I measured them all and randomly divvied them up into three food treatments. One group remains on the pink coralline alga they’d all been eating once they graduated from a diet of scum, one group gets to eat the soft green alga Ulva sp., and the third group is eating the kelp Macrocystis pyrifera. I fully expected that the urchins on coralline algae would grow much more slowly and experience higher mortality than the other groups. And now I have data to validate my intuition!

Test diameter of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 3 August 2015. © Allison J. Gong
Test diameter of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 3 August 2015.
© Allison J. Gong

It has been clear from the get-go that the Ulva and Macrocystis urchins are growing faster than the poor guys relegated to coralline algae. The coralline urchins are hanging in there, though, and are even growing a bit. They are also dying, a lot.

Population sizes of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 3 August 2015. © Allison J. Gong
Population sizes of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 3 August 2015.
© Allison J. Gong

During the first month of the experiment I was surprised to see the high attrition rate of urchins eating Macrocystis. I think these early deaths were due to the fact that Macrocystis, once it starts to go bad, goes bad fast. Even with daily water changes to rinse out the poop, the Macrocystis bowl tended to get dirty faster than the others, so poor water quality may have killed the urchins. The copious slime from the Macrocystis itself doesn’t help, either. Eventually I will be able to graduate the urchins to containers that will allow flow-through water, but for now most of them are too small to be kept in screened containers because they would escape through the mesh.

Overall, the Ulva urchins seem to be the happiest. I haven’t lost any this past month and they eat and poop a lot. These individuals have the good fortune that Ulva doesn’t foul the water as quickly as Macrocystis does. They are extraordinarily beautiful, too, and are becoming much more colorful:

Juvenile sea urchin (Strongylocentrotus purpuratus), age 196 days. 3 August 2015. © Allison J. Gong
Juvenile sea urchin (Strongylocentrotus purpuratus), age 196 days. 3 August 2015.
© Allison J. Gong

I’ve always wondered about the biochemical magic that allows this species of sea urchin to eat algae (primarily kelps, but also some red and green algae) and end up so unabashedly purple as they grow to adulthood. I know from experience in the intertidal that juveniles of S. purpuratus usually go through a green stage when they’re in the 1-2 cm size range, before they become purple. And once they’re purple, they stay purple. Part of the reason I wanted to do this feeding experiment is to see how the juvenile diet affects color of the animal. These urchins are all from the same mating, so they are full siblings. Presumably there would be some color variation even among a cohort of full-sibs, but if I can distinguish differences between urchins eating Ulva and urchins eating Macrocystis, then perhaps these would be at least partly due to diet?

The difficulty is in photographing individual urchins under the same lighting and background conditions so that color can be somewhat objectively registered. I’m going to have to become a much better photographer, and the urchins are going to have to be more willing to sit still and pose for me. In the meantime, it is easier to compare overall color between the two groups, rather than individual urchins. Looking at the two bowls side-by-side, I get a better feel for the gestalt of each group; can you see the difference? Before you read the caption, can you guess which is the Ulva group and which is the Macrocystis group?

Juvenile sea urchins (Strongylocentrotus purpuratus), age 196 days. Urchins on the left are eating the green alga Ulva; urchins on the right are eating the kelp Macrocystis. 3 August 2015. © Allison J. Gong
Juvenile sea urchins (Strongylocentrotus purpuratus), age 196 days. Urchins on the left are eating the green alga Ulva; urchins on the right are eating the kelp Macrocystis. 3 August 2015.
© Allison J. Gong

To my admittedly very subjective eye, the urchins on the left have more dark pigment and the ones on the right have a more overall golden color. The golden color makes sense because Macrocystis is golden in color (even though taxonomically it is considered a brown alga). But the darker purple in the urchins eating green algae? That makes less sense to me. In any case, I’ll have to wait and see how the color develops in both groups of urchins. I suspect that in the long run they’ll all end up purple, because that’s what they do in the field, but they may take different routes getting there. Stay tuned!

A star is born!

Posted on by Allison J. Gong

I’m sorry. I had to go there. You didn’t really expect me not to, did you?

The reason, of course, is that today we got our first settled and metamorphosed Pisaster stars! We were doing our normal Monday water change when I noticed a teensy orange speck on the bottom of one of the jars. I used my beat-up old paintbrush to remove the tiny dot to a dish, put it under the dissecting scope, and saw this:

Metamorphosing ochre star (Pisaster ochraceus), age 48 days. 20 July 2015. © Allison J. Gong
Metamorphosing ochre star (Pisaster ochraceus), age 48 days
20 July 2015
© Allison J. Gong

From this picture it’s a little hard to see what’s going on. The entire body has contracted a lot, from a 2.5-mm larva to about 1/4 of the original size as a 600-µm juvenile, and become much more opaque. There are tube feet and spines as well as some remnants of larval body (the soft bits at the bottom of the animal) at this in-between larvenile stage.

Here’s a picture of a fully metamorphosed little star:

Newly metamorphosed ochre star (Pisaster ochraceus), age 48 days. 20 July 2015. © Allison J. Gong
Newly metamorphosed ochre star (Pisaster ochraceus), age 48 days
20 July 2015
© Allison J. Gong

I expect we’ll be seeing more tiny orange dots on the bottoms and sides of the jars in the next several weeks. At some point we will have to figure out what they eat and provide it for them. But at least we know we’re able to get them through the larval phase.

Just for kicks, here are some pictures of where we grow the larvae and how we do the twice-weekly water changes.

Larval culturing paddle table. © Allison J. Gong
Larval culturing paddle table.
© Allison J. Gong
Step 1: We pour the larvae into a filter to concentrate them into a smaller volume of water. Then we can wash or rinse the jar. © Allison J. Gong
Step 1: We pour the larvae into a filter to concentrate them into a smaller volume of water. Then we can wash or rinse the jar.
© Allison J. Gong
Steps 2 and 3: We use a turkey baster to transfer most of the larvae from the filter into a jar of clean water. The final step is to turn the filter over and wash the last larvae into the jar. © Allison J. Gong
Steps 2 and 3: We use a turkey baster to transfer most of the larvae from the filter into a jar of clean water. The final step is to turn the filter over and wash the last larvae into the jar. Then we fill up the jar and resume the stirring.
© Allison J. Gong

An update on other matters:

Today is the six-month birthday of my baby urchins! Six months ago to the day these little guys were zygotes, and six-months-plus-one-day ago their parents were roaming the intertidal. They grow up so fast!

Juvenile sea urchin (Strongylocentrotus purpuratus), age 6 months. 20 July 2015. © Allison J. Gong
Juvenile sea urchin (Strongylocentrotus purpuratus), age 6 months
20 July 2015
© Allison J. Gong

And lastly, that little shmoo-type thing that I found in the plankton yesterday has revealed itself to be. . . an anemone!

One of the things I like best about cnidarians is the beautiful transparency of their bodies. I love how you can see fluid circulating through the tentacles. Gorgeous, isn’t it?

The perfect storm

Posted on by Allison J. Gong

Although the last thing that any of us marine invertebrate biologists want to see again is a wasted sea star, the syndrome has once again been making its presence felt at the marine lab. It has been almost two years since I documented the initial outbreak, and while nobody is convinced that it has entirely run its course, most of us, myself included, had thought that perhaps the first wave had passed. Then, back in March of this year, I saw one of my stars doing this:

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

Those large white blotches on the aboral surface are open wounds, or lesions, through which some of the animal’s innards are protruding. The arm towards the top of the photo has also begun dissolving, literally wasting away into the environment. The lesions eat right through the epidermis, liberating the skeletal ossicles that lie underneath it; I’ve circled two of them on the right side of the photo and there are two more at the bottom.

The discovery of this wasting animal was alarming and for a while I held my breath whenever I check on stars at the lab, but after several weeks of not seeing any additional sick animals I relaxed my guard and concluded the incident was a one-off. So imagine my horror to walk in this morning and see this in one of my tables:

Oral surface of a wasting bat star (Patiria miniata), 17 July 2015. © Allison J. Gong
Oral surface of a wasting bat star (Patiria miniata)
17 July 2015
© Allison J. Gong

Sea stars generally don’t just lie on their aboral surfaces, and this animal was making no attempt to right itself. See how the margin between the arms is a little wavy? That isn’t normal, either, and shows that the animal’s ability to regulate its internal water content has been compromised. And while bat stars routinely scavenge by extruding their stomachs through the mouth and digesting whatever it comes into contact with, they don’t leave the stomach hanging outside the body when they aren’t feeding.

All of which gave me a bad feeling in the pit of my own stomach, which only got worse when I turned the animal over:

Bat star (Patiria miniata) with several small aboral lesions, 17 July 2015. © Allison J. Gong
Bat star (Patiria miniata) with several small aboral lesions
17 July 2015
© Allison J. Gong

The animal appears deflated and has small lesions all over its aboral surface. I was feeling a little deflated myself when I saw this. With stars it can be difficult to determine just how alive (or how dead) an individual is. This one didn’t fall to pieces when I picked it up, which didn’t exactly surprise me because Patiria is less prone to losing its arms via autotomy than the Pisaster species (ochre, short-spined, and jewel stars) and Pycnopodia helianthoides (sunflower star), in whom one of the symptoms of wasting syndrome is a violent ripping off of one’s own arms. I suppose this makes the whole episode marginally less horrific than when I saw my Pisaster stars wasting, or maybe I’ve become jaded.

In any case, I had to decide what to do with this sick star. It was in a table with half a dozen other bat stars, so whatever it was exposed to or was itself exuding has already been spread to the others. I couldn’t leave it there to rot in place, but neither did I want to throw it away if it was still somewhat alive. I turned the animal so it was oral-side-up again and left it alone to see what would happen. If it righted itself I’d assume it was more or less alive and isolate it in a quarantine tank; if it didn’t, then all hope was lost and it could be tossed. When I was ready to leave the lab several hours later, it was in the exact same position. Verdict: dead.

So, why now? I’ve been thinking about this, and here’s what I came up with. The densovirus that has been linked to sea star wasting syndrome is always around in the environment. Like other opportunistic pathogens it doesn’t usually cause a problem until a host organism becomes stressed or compromised. For the past two years we’ve been aware of wasting events up and down the coast, which wiped out the most vulnerable individuals. Animals with resistance, however, were able to survive. The survivors may have been weakened, though, and the mild El Niño of 2014 and the much stronger one we have now in 2015 have resulted in water temperatures much higher than normal. I haven’t plotted the data yet, but in June and July the water temperature has been hovering at 15-16°C, with jumps this week up to 18.5°C over the past couple of days. These warmer temperatures can be very stressful to animals, which may be just what the densovirus needed to “announce [its] presence with authority” (that’s a quote from my favorite baseball movie, Bull Durham). Outbreaks of wasting syndrome are probably caused by a combination of factors: population density of the host animal, presence of the densovirus, overall health of the host, water temperature, water chemistry, and others I haven’t thought of. We are certainly not close to a complete understanding of this phenomenon.

At this point I don’t have many stars left in my collection. I hope I get to keep them.

All in the family

Posted on by Allison J. Gong

Earlier this week an acquaintance asked me about the development of sand dollars, specifically if it is anything like that of sea urchins. It just so happens that sea urchins and sand dollars, while not in the same taxonomic family, are in the same class, the Echinoidea. As close kin, they share a similar larval form, the pluteus larva, and undergo more or less the same development. If you’re satisfied with the short answer, you can stop reading here.

Interested in the details? Then read on!

In my first year of graduate school I took a course in comparative invertebrate embryology through the University of Washington up at the Friday Harbor Lab in Puget Sound. It was a blast! We spent mornings in lecture and afternoons in the field and/or in the lab observing and drawing embryos and larvae. At night we would lie on our bellies on the dock and shine a light over the water, scooping up the critters that rose to the surface. It was in this class that I did my first studies of larval development and fell in love with the echinopluteus. In that class we studied several echinoid species, but the only one I was able to follow all the way through to metamorphosis was the sand dollar Dendraster excentricus.

Even a casual beachcomber has likely encountered the naked tests of dead sand dollars, but I’d bet that most people haven’t seen them alive. The bare test is white, while in life the animal is a fuzzy grayish-purple color. As their name indicates, they live on sandy bottoms in the shallow subtidal, where they prop themselves in the sand and catch particles of food that fall on them. This photo below is of the sand dollar exhibit at the Monterey Bay Aquarium. My friend, Chris Mah, is the owner of the most excellent Echinoblog and has explained how sand dollars really are sea urchins. Check it out for some good information from a real-life echinodermologist (yes, I just made up that word).

Dendraster excentricus, the eccentric sand dollar. © Monterey Bay Aquarium
Dendraster excentricus, the eccentric sand dollar.
© Monterey Bay Aquarium

But the original question I was asked to address is about the development of sand dollars as it compares to that of sea urchins. Given that these animals share the same larval form, you would probably not be surprised to learn that their overall development is very similar. Just to remind myself of exactly how similar, I dug through my old embryology notebook and took pictures of some of my drawings. Keep in mind that these drawings were intended to document my observations, not to be pretty or artistic. However, they may be useful as comparisons with the photos of sea urchin larvae that I’ve been taking over the years.

Early pluteus larva of Dendraster excentricus (eccentric sand dollar), drawn from life. © Allison J. Gong
2-day-old early pluteus larva of Dendraster excentricus (eccentric sand dollar), drawn from life.
© Allison J. Gong

According to my notes, to speed up development we cultured these larvae at room temperature so we could get through the entire larval period in the 5-week course. I didn’t record the temperature, but would guess it to be about 17ºC. At this temperature it took the Dendraster larvae only two days to get to the early pluteus stage, complete with functioning gut and skeletal rods (see drawing on right).

In contrast, the Strongylocentrotus larvae that I started this past January were still forming their guts at the ripe old age of 2 days. You’ll have to take my word for that, as I didn’t take pictures. I do have a photo of the embryos when they were 1 day old and had just hatched:

1-day-old embryos of S. purpuratus. The empty space inside each embryo is called the blastocoel. 20 January 2015. Photo credit: Allison J. Gong
1-day-old embryos of S. purpuratus
21 January 2015
Photo credit: Allison J. Gong

By the age of 7 days, the Dendraster larvae already had three pairs of fully developed arms (the anteriolateral, postoral, and posterodorsal arms), with the fourth and final pair (the preoral arms) just beginning to form:

7-day-old pluteus larva of Dendraster excentricus. © Allison J. Gong
7-day-old pluteus larva of Dendraster excentricus, drawn from life.
© Allison J. Gong

The Strongylocentrotus larvae, on the other hand, had barely started growing their first arms at 6 days of age:

6-day-old pluteus larva of Strongylocentrotus purpuratus. © Allison J. Gong
6-day-old pluteus larva of Strongylocentrotus purpuratus
26 January 2015
© Allison J. Gong

After a few weeks the Dendraster larvae had grown all four pairs of their arms as well as their juvenile rudiment on the left side of the gut. The individual I drew has a fully formed rudiment with five tube feet (labelled ‘podia’ in the drawing) and an additional waviness to the ciliated band (shaded in the drawing). My guess at the time was that this individual was developmentally competent, or ready to settle out of the plankton and metamorphose.

27-day-old pluteus larva of Dendraster excentricus. © Allison J. Gong
27-day-old pluteus larva of Dendraster excentricus, drawn from life.
© Allison J. Gong

Most of the sea urchin larvae had not even started forming rudiments by the age of 31 days:

31-day-old pluteus larva of Strongylocentrotus purpuratus, 20 February 2015. © Allison J. Gong
31-day-old pluteus larva of Strongylocentrotus purpuratus
20 February 2015
© Allison J. Gong

When I was in Friday Harbor I was lucky to see one of my Dendraster larvae undergo metamorphosis more or less as I was watching under a microscope. I wish I’d had the set-up to take microscope pictures, because it was an amazing phenomenon to observe. I did make one last drawing of the newly metamorphosed and benthic tiny sand dollar and its discarded larval skeletal rods:

Newly metamorphosed Dendraster excentricus, drawn from life. © Allison J. Gong
Newly metamorphosed Dendraster excentricus, age 29 days, drawn from life.
© Allison J. Gong

I’m sure that I drew what I saw, but looking at this drawing with more experience I wonder if the tube feet really looked like that. Oh well. One of the last things we did as a class was “graduate” our remaining larvae off the dock and wish them luck as we released them into the real world.

With my most recent batch of S. purpuratus larvae, I began seeing competence at 45 days post-fertilization. The first bona fide juvenile urchin didn’t begin crawling around on tube feet until 50 days:

Newly metamorphosed Strongylocentrotus purpuratus, age 50 days. 11 March 2015. © Allison J. Gong
Newly metamorphosed Strongylocentrotus purpuratus, age 50 days
11 March 2015
© Allison J. Gong

The next logical question would be: Why do the sand dollars develop so much more quickly than the urchins? I don’t have a definitive answer for that. Since that class in Friday Harbor I haven’t had another chance to study sand dollars, but in my experience my most recent cohort of sea urchins progressed through development at the normal pace for the species in this location. Some species just take longer than others, and the differences could be due to any number or combination of factors: water temperature, genetics, presence or absence of settling cues, water chemistry, and so on. The take-home message, if you’ve managed to read this far, is that yes, sand dollars and sea urchins undergo pretty much the same development. It’s the same as the short answer at the top of the post, but wasn’t it fun getting there the long way?

You are what you eat, part the first

Posted on by Allison J. Gong

Remember those little urchins I brought into the world back in January? Well, they’re doing well, for the most part. About a month ago I took about 250 of them, measured them, and divided them into three feeding treatments:  one group I left on the coralline rocks they all cut their teeth on, one group is eating the green alga Ulva, and the third group is eating the kelp Macrocystis pyrifera. My plan is to keep the groups on these foods and monitor growth and survival.

After one month it appears that mortality and growth are not related. I have lost more urchins from the Macrocystis treatment than from the other two, and yet those that have survived this far have grown quite a bit. A month of the experiment gives me exactly two data points, which may over time indicate the beginning of a trend but for now are entirely meaningless. I’ll have to wait at least another month to see if what’s happening now continues.

However, I also took pictures of the urchins, and some of them are getting so pretty! I’m curious to see if the two macroalgal diets (Macrocystis and Ulva) affect the color of the urchins as they grow. Of course, color is very subjective and I can’t duplicate the exact lighting conditions when I take microscope pictures of different subjects, so at this point they all look the same no matter which food they’ve been eating.

Juvenile Strongylocentrotus purpuratus feeding on Macrocystis pyrifera, age 167 days. 6 July 2015. © Allison J. Gong
Juvenile Strongylocentrotus purpuratus feeding on the kelp Macrocystis pyrifera, age 167 days. Major mark on scale bar indicates 1 cm
6 July 2015
© Allison J. Gong

and

Juvenile Strongylocentrotus purpuratus feeding on the green alga Ulva sp., age 167 days. 6 July 2015. © Allison J. Gong
Juvenile Strongylocentrotus purpuratus feeding on the green alga Ulva sp., age 167 days
6 July 2015
© Allison J. Gong

My most colorful urchin at the moment is a little guy from the Ulva food treatment. Its test diameter is only about 4 mm, but its color is very vibrant:

Juvenile Strongylocentrotus purpuratus, age 167 days. 6 July 2015. © Allison J. Gong
Juvenile Strongylocentrotus purpuratus, age 167 days
6 July 2015
© Allison J. Gong

In addition to the five distinct reddish-purple bands on the body, I like that this urchin has so much color on its spines. This individual looks like it may skip the green stage that urchins of this species go through and go straight to purple.

Aren’t these animals beautiful?

Got ’em!

Posted on by Allison J. Gong

When I moved to the coast these many years ago and started poking around in the local intertidal, I became entranced with little animals called staurozoans. I can’t claim to have been to every intertidal site in the area, but I’ve been to several of them and I personally know the staurozoans to occur at only two sites: Carmel Point (I’ve seen them there once) and Franklin Point (I used to see them there fairly regularly). In 2007 I went out to Franklin Point every month that had a negative low tide during daylight hours to monitor the abundance and size of the staurozoans; heck, once I even went out in the dark armed with a headlamp and a friend who was supposed to watch my back but instead fell asleep against the cliff. The staurozoans were easy to find that year and occurred in large numbers.

I used to be able to find the staurozoans in one particular area on the north side of Franklin Point where the water continually swashes back and forth.

Intertidal at Franklin Point, 3 July 2015. © Allison J. Gong
Intertidal at Franklin Point
3 July 2015
© Allison J. Gong

The staurozoans would always be attached to algae, often perfectly matching the color of their substrate. I remember seeing two versions, one a reddish brown and the other a vibrant bottle green color, of the same species of Haliclystus.

In March of this year I saw a lot of small staurozoans when I braved the afternoon winds at Franklin Point. The conditions were pretty horrid, with the water all churned up and murky so I couldn’t take any pictures, but I was happy to see my little guys because it meant they were there. I hadn’t seen them for a few years before this past spring and was beginning to doubt my search image. Huzzah for validating my gut feeling! I may have whooped and done the happy dance in my hip boots that afternoon.

Fast forward almost three months and three additional trips out to Franklin Point before I found a staurozoan this morning. One. And it was only about 0.5 cm tall, the same size that they were in March. And it was brown, the same color as most of the algae out there. Because they live where the water is constantly moving it’s really hard to photograph them in situ. This is the best I could do:

Haliclystus sp. in situ at Franklin Point, 3 July 2015. © Allison J. Gong
Haliclystus sp. at Franklin Point
3 July 2015
© Allison J. Gong

It’s hard to appreciate from this photo just how beautiful these animals are. They are very animated, swaying in the current and although they are attached they can slowly creep over surfaces or even detach, somersault around, and re-attach. Back in the day when I used to find them frequently I brought some back to the lab to observe them more closely. I could get them to feed, but they never lasted more than about a week in captivity.

So, what exactly are staurozoans? They are cnidarians, kin to sea anemones, hydroids, Velella velella, and jellies. Their common name is stalked jellies, and for a long time biologists considered them to be closely related to the jellies in the cnidarian class Scyphozoa. However, recent studies of the genetics of staurozoans have caused taxonomists to elevate these creatures to their own class, the Staurozoa.

Not much is known about the ecology of Haliclystus in California, probably because they are so damn difficult to find in the field. I have one or maybe two more trips out to Franklin Point this summer before we lose the minus tides for the season; hopefully they will still be there. I’d love to get some better pictures of them to show my students this fall. Wish me luck!

Constellations

Posted on by Allison J. Gong

I did a quick search, and there doesn’t seem to be a collective noun for sea stars. I’m going to remedy that by declaring “constellation” to be the official term for a group of sea stars. And by “official” I mean that’s the term I’m going to use. Who knows, maybe it’ll take.

In any case, I certainly have a constellation of sea star larvae in each of my jars. Today I pipetted a lot of them into a bowl, and they look pretty cool all swimming together, like strange alien spaceships. What do you think?

The largest of the larvae are over 2 mm long now, and the brachiolar arms have grown much longer. They have three adhesive papillae on the ventral side of the anterior projection and well-formed juvenile rudiments, where the water vascular system is forming. They’re much too big to fit under the compound scope, so the only way to get pictures of the entire body is through the dissecting scope:

Brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015. © Allison J. Gong
Brachiolaria larva of Pisaster ochraceus, age 31 days
3 July 2015
© Allison J. Gong

In the above photo you are looking at the larva’s ventral surface, so the animal’s left side on the right side of the photo, and vice versa. If you squint you might be able to convince yourself that you see a small whitish bleb on the left side of the stomach; that’s the rudiment. Since it doesn’t make much sense under this magnification, I removed this individual to a slide and put it under the compound scope. It doesn’t fit in the field of view, so I took pictures of each half of the body. If I were clever with photo editing software I’d be able to mesh these photos into a single image. Alas….

Ventral view of the anterior end of a brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015. © Allison J. Gong
Ventral view of the anterior end of a brachiolaria larva of Pisaster ochraceus, age 31 days
3 July 2015
© Allison J. Gong
Ventral view of the posterior end of a brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015. © Allison J. Gong
Ventral view of the posterior end of a brachiolaria larva of Pisaster ochraceus, age 31 days
3 July 2015
© Allison J. Gong

This gives you a better view of the juvenile rudiment on the animal’s left. Those three roundish blobs are tube feet! I think it’s likely that at some point in the not-too-distant future the larvae will be competent, which means they’d be physiologically and anatomically capable of metamorphosis. It seems to me that they are still developing very quickly, and with seawater temperatures consistent at 15-16°C I don’t expect that to change. So far, so good!

Edit 4 July 2015:  Look at what my online friend Becca can do! She was able to merge my photos into a single image. Now you can see the entire body! Thanks, Becca!

Composite image of brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015.
Composite image of brachiolaria larva of Pisaster ochraceus, age 31 days
3 July 2015

So big, so fast!

Posted on by Allison J. Gong

I am astonished at how quickly my Pisaster larvae are growing and developing. This week saw their 3-week birthday, and today they are all of 24 days old. And look at how much they’ve changed since Monday!

Brachiolaria larva of Pisaster ochraceus, age 24 days. 26 June 2015. © Allison J. Gong
Brachiolaria larva of Pisaster ochraceus, age 24 days
26 June 2015
© Allison J. Gong

This individual measures 1500 µm long, not including the length of those two long brachiolar arms on the posterior end. The main part of the body barely fits in the field of view under the lowest magnification of my compound microscope. Those long arms are very flexible, and today I observed that the animal reacts to sudden bright light by flipping them up towards the anterior end. The body can be scrunched into a surprisingly small ball, too, as I saw when I sucked it up into a pipet. Lacking the skeletal arm rods of the sea urchin’s pluteus larva, this brachiolaria’s entire body can be squished and flexed along any axis.

This video shows a little of how the brachiolaria larva moves around. I’ve trapped it under a cover slip in a large drop of water on a depression slide so it can’t swim away, but isn’t being harmed. If you look closely you can see how tiny food cells are swept along by the current generated by the ciliated band. This is a ventral view, so you are looking down on the larva’s front. The anterior end is to the left.

I’ve also been playing around with darkfield lighting, just because it’s fun. Everybody should do things just because they’re fun. Sometimes the fun stuff is also really cool:

Brachiolaria larva of Pisaster ochraceus, age 24 days. 26 June 2015. © Allison J. Gong
Brachiolaria larva of Pisaster ochraceus, age 24 days
26 June 2015
© Allison J. Gong

While I had the darkfield lighting working I shot another video, this time focusing through various focal planes to show the three-dimensional structure a bit more. You can still see the food particles zooming around.

The next major developmental hurdle for me to look for is the formation of the juvenile rudiment. I expected to have another couple of weeks before rudiments would start forming, but given how fast things are happening I might not have much more time at all.

Why are these larvae developing so quickly? We know that development and growth rates for many marine invertebrates are temperature-dependent: both occur more quickly at higher temperatures. Surface seawater temperatures at the marine lab have been elevated for the past few weeks, hovering at 14-16.5°C for as long as these larvae have been alive. The warmer water increases metabolic rate, thus faster growth and development.

Is this a good thing or a bad thing? Well, that’s what I’m not sure of. My gut feeling is that it could be either, depending on food availability. One risk of higher metabolic rate is that the animal burns through its food supply more quickly. We can mitigate that risk by making sure that the larvae get fed every day and that their guts remain full at all times. Another risk of fast growth is the larvae could reach the developmental stage at which they could undergo metamorphosis, but not have had time to stockpile enough energy reserves to make it through the metamorphic process or survive long enough post-metamorphosis to grow the juvenile gut and begin feeding.

I can’t do anything about the elevated water temperatures, so will just have to wait and see what happens with these larvae.

Some smells linger for days

Posted on by Allison J. Gong

A few months ago, a former student invited me to participate in an activity with local Girl Scouts. The Scouts have a camp this weekend at Henry Cowell Redwoods State Park, and this year their theme is “Commotion in the Ocean.” The former student, whose name is Thomas, works for the Squids for Kids program run jointly by the Hopkins Marine Station (the marine lab facility of Stanford University) in Pacific Grove and the NOAA Southwest Fisheries lab here in Santa Cruz. Squids for Kids provides Humboldt squids (Dosidicus gigas) to schools and other kid-focused programs around the country, along with instructions on how to dissect the squids and identify their parts. I think the way it worked is that the Girl Scouts applied for squid and Thomas was assigned the event. He invited me to join him because the Scouts thought it would be good for the girls to see a woman doing the dissection and getting all dirty.

Standard disclaimer: I feel very uncomfortable when people ask me to be a role model for girls, boys, women, men, whoever. It makes me feel self-conscious, as though I’m being scrutinized for a certain intangible quality of role-model-ishness and could somehow come up failing, and that I have to be better than I actually am. So I always go into these things with a little apprehension.

The thing about dissecting a Humboldt squid is that you can’t go just part of the way into a squid; you have to dive in with both hands and resign yourself to the smell. Humboldts are large animals, compared to the ones I’m used to working with, and are easy to dissect:  All you do is make a cut open the mantle and all the internal organs are there to observe.

Thomas shows the girls what the Humboldt squid (Dosidicus gigas) is all about, 26 June 2015. © Allison J. Gong
Thomas shows the girls what the Humboldt squid (Dosidicus gigas) is all about
26 June 2015
© Allison J. Gong

Problem with just diving into a squid is that once you do, you can’t take any more pictures because your hands get all gunked up. This is the only photo I snapped of the morning’s activities before things got very smelly. I really didn’t want to smell it on me for the next three days so I wore a lab coat and a glove on my left hand, leaving my right hand “clean” so I could drink my tea and keep an eye on the time. Even so, my right hand still has a bit of squid stink after several hours of near-continual dunking in either seawater or hot freshwater. Maybe I’m just imagining that I still smell it.

Experiences like today remind me that I’m not very good with young kids. I am simply not accustomed to dealing with their short attention spans and don’t know how to distill an explanation into 25 words or fewer, which is what seems necessary for the youngest Girls Scouts at camp today.

That said, there was one girl I found very intriguing. I don’t know her real name but her camp name was Rockcod. She was maybe 9 or 10 years old. She didn’t want to touch any part of the squids even though her friends were getting in there and touching the gills, eyeballs, tentacles, and innards. Rockcod told me that her dad does a lot of fishing and she goes with him. They’ve never caught squids but catch lingcods and various rockfishes, which they take home and eat. Her uncle once caught a yellowfin tuna that was “as big as the table,” probably about four feet long.

Despite adamantly not wanting to touch the squids, Rockcod was clearly fascinated by them. She left our station to participate in other activities but kept coming back and asking questions. She wanted to know what all the parts were and really wanted to be around when we opened up the next squid. She asked all the right questions:

  • How do you know if it’s a boy or a girl?
  • Where is the ink? Can you write with it?
  • How come two of its arms are so much longer than the others?
  • Where is the mouth?
  • A squid has three hearts? No way!
  • Can you eat it?
  • What do they eat?

Several of the other girls (and most of their adult chaperones) were a bit squeamish and/or offended by the smell. I heard “Ew, that stinks!” more than a few times. Well, they do stink, there’s no getting around it. Still, I’d rather smell an honestly dead squid than one that has been preserved in formaldehyde. And you do get used to the smell after a while. Except that I still catch a whiff of it emanating from somewhere on my body every once in a while. Hopefully it goes away with my next shower.

And I did get a thank-you gift!

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