Tag: marine invertebrates

Playing matchmaker

Posted on by Allison J. Gong

We are finally heading into the time of the year that our local intertidal sea urchin, Strongylocentrotus purpuratus, spawns. Usually I would wait until December or January to try to spawn urchins in the lab, but next week my students will be dissecting urchins in lab and I thought I might as well evaluate gonad development in the animals that are going to be sacrificed anyway. In early December I’m going to loan several urchins to a colleague who will be spawning them to show the earliest stages of development to students in one of the lower-division classes at the end of the semester. If I have any luck today, I’ll be able to: (1) start my own cultures of urchin larvae so that I can show the later larval stages to students in my upper-division class; and (2) let my colleague know how likely it is that the urchins I loan to her will be spawnable.

4 November 2015 © Allison J. Gong
4 November 2015
© Allison J. Gong

I know, it ain’t as romantic as the Ritz-Carlton but this is where I hope to make the sea urchins have sex. We have our victims lucky individuals in their “live only” tub, two beakers for eggs, two sperm dishes on ice, a box of glass pipets, a bottle of magic juice, and a syringe with needle to get the magic juice into the animals. Ready to go!

What is the magic juice, you ask? It’s a solution of KCl in filtered seawater. I’m not sure exactly how it works, but here’s what I think happens. We use a solution of MgCl2, a similar salt, to narcotize animals before dissecting them. Sea urchins sitting in a bath of  MgCl2 isotonic with seawater get sleepy pretty quickly, becoming entirely nonresponsive after about 30 minutes. I suspect that KCl has a similar effect. We inject KCl into the main body cavity of the urchin (I call this “shooting them up”) and I think it relaxes the muscles surrounding the gonopores. If the gonads are ripe, then gametes are released as the gonopores open. If gonads are immature, then nothing happens.

A sea urchin is a well-armored beast. Its endoskeleton, or test, is a solid structure composed of calcareous ossicles that are perforated only where tube feet extend. Getting a needle through the test without damaging the animal is pretty much impossible, so we go through the peristomial membrane instead. This membrane surrounds the mouth on the oral (bottom) side of the urchin. It’s the only way to get into an urchin without breaking the test.

The urchins don’t seem to like being injected with KCl–they wave their tube feet and spines all around and generally appear somewhat agitated–but they don’t suffer any lasting effects.

If the urchins are ripe, they should start spawning shortly after being injected with KCl. Sometimes the response is immediate, with urchins pouring out gametes through all five gonopores at an astounding rate. Today it was much slower. It took about 5 minutes for the first female to spawn:

Spawning female sea urchin (Strongylocentrotus purpuratus). 4 November 2015 © Allison J. Gong
Spawning female sea urchin (Strongylocentrotus purpuratus).
4 November 2015
© Allison J. Gong

That little blotch of pale orange is is the mass of eggs that she is spawning. At this point you can pipet off the eggs into a beaker of filtered seawater, but I decided to go the less-invasive route and simply invert the spawning animal onto a beaker filled with water and let the eggs drop to the bottom as they flowed out of her.

The only difficulty with this method is that the animal doesn’t like being upside down and immediately tries to right herself. I kept having to remove her from the beaker and replace her in the orientation we wanted. I designated this urchin as F1. She gave us a decent number of eggs. A second, smaller female (F2) spawned just a few eggs but we kept them all.

Sperm get a different treatment. I had only one male spawn this morning and he wasn’t exactly a gusher. I pipetted off the concentrated sperm into a cold dish on ice, and didn’t dilute the sperm until the eggs were ready for fertilization.

UP NEXT: Fertilization and subsequent events.

You are what you eat, part the fourth

Posted on by Allison J. Gong

The juvenile sea urchins I’ve been raising this year are now nine months old. Back in June I put them on three different macroalgal diets and have been measuring their test diameters monthly. I do the measuring in the first week of every month, and today was the day for November. Over the past few weeks I lost a lot of my Ulva urchins, for no reason that I could discern. Judging from the poop production they were definitely eating, but on some days there would be a handful of corpses in the bowl when I changed the water. They all seemed healthy and happy today, including this beautiful creature:

Juvenile sea urchin (Strongylocentrotus purpuratus) that has been eating Ulva, age 9 months. 2 November 2015 © Allison J. Gong
Juvenile sea urchin (Strongylocentrotus purpuratus) that has been eating the green alga Ulva sp., age 9 months.
2 November 2015
© Allison J. Gong

Seriously, this has to be the most gorgeous photo of a sea urchin I’ve ever taken. This individual is the largest of my Ulva urchins, with a test diameter of 12.7 mm. I love the coloration of this animal: the younger spines are green, the older spines are pale purple, and the tube feet are beautifully transparent and tipped with purple suckers.

By contrast, the urchins eating Macrocystis continue to be a more uniformly golden color:

Juvenile sea urchin (Strongylocentrotus purpuratus) that has been eating the kelp Macrocystis pyrifera, age 9 months. 2 November 2015 © Allison J. Gong
Juvenile sea urchin (Strongylocentrotus purpuratus) that has been eating the kelp Macrocystis pyrifera, age 9 months.
2 November 2015
© Allison J. Gong

This Macrocystis urchin is actually a tad bigger than the Ulva urchin and has a test diameter of 13.0 mm. It looks smaller because its tube feet are fully extended, so I had to zoom out a bit to get the entire body in the frame. It was also crawling around very fast and I had to hold it down to get it centered, then remove the forceps and take the picture quickly before it walked out of the picture. Every photo of this individual that I managed to get is a little blurry because of the movement.

Last but not least, the urchins eating coralline algae are hanging in there. None of them died in the past month and they are growing. Their color patterns are qualitatively different from the those of urchins eating Ulva or Macrocystis. To my eye there is more contrast in the coralline urchins; they all seem to have prominent dark coloration in the lines that radiate outward from the apical region. The other urchins have it too, but in the coralline urchins this dark pigmentation is concentrated into more clearly defined streaks and contrasts more strongly with the paler background color.

Juvenile sea urchin (Strongylocentrotus purpuratus) that has been eating coralline algae, age 9 months. 2 November 2015 © Allison J. Gong
Juvenile sea urchin (Strongylocentrotus purpuratus) that has been eating coralline algae, age 9 months.
2 November 2015
© Allison J. Gong

This animal, with a test diameter of 6.08 mm, is about half the diameter of the largest of its full siblings in each of the other food treatments. Food quality definitely has an effect on size, as these data indicate:

Test diameters of juvenile sea urchins (Strongylocentrotus purpuratus) on three food treatments. 2 November 2015 © Allison J. Gong
Test diameters of juvenile sea urchins (Strongylocentrotus purpuratus) on three food treatments.
2 November 2015
© Allison J. Gong

It remains to be seen whether or not I’ll be able to provide Ulva and Macrocystis to these animals throughout the winter. If we get the strong El Niño storms that are predicted, the nearshore algae could be wiped out for a while. I’ll make sure that if I run out of one food then urchins in the other treatment will also fast until I can feed both of them again. In the meantime, because the coralline urchins are so far behind in their growth, I’ll continue to give them access to food. I don’t want any of them to die of starvation, and the coralline eaters are the most vulnerable, I think.

Feeding the ‘droids

Posted on by Allison J. Gong

So, those bits of Ectopleura crocea that I grabbed from the harbor on Monday are voracious eaters. I didn’t feed them yesterday because I didn’t have time and the students spent the afternoon looking at them in lab, and I hoped that they’d be alive today. Some of the stalks had dropped their hydranths (the distal part that bears the feeding tentacles, mouth, and reproductive gonophores) but most of them were alive and lovely. I had a nice fresh batch of brine shrimp all hatched out and ready to go and thought I’d see if the hydranths could eat them. Little did I know that this simple exercise would occupy most of my day.

I started by squirting some of the brine shrimp onto the hydranths, which for the most were pretty lackadaisical about catching them. Then I decided to feed them the mashed up brine shrimp that I’m still feeding the tiny Melibe and WOW! that did the trick! Maybe it was the scent of the macerated brine shrimp that triggered the feeding response. I was fascinated.

They are beautifully and unexpectedly animated animals.

After I watched them feed for a while, it seemed to me that the outer ring of tentacles catches and holds onto prey, while the prehensile manubrium swings around and brings the mouth into contact with the food. In the meantime, while all this brine shrimp catching is going on there are other larger crustaceans crawling all over the hydranths, even onto the tentacles, without getting stung. I think their exoskeletons must be thick enough not to be penetrated by the hydroid’s cnidocytes (stinging cells).

Having discovered the trick to making the hydranths eat, I squirted brine shrimp mush on them and left them alone for about 20 minutes. When I came back they had eaten and I could see brine shrimp in their guts, so I gave them more. The feeding response was pretty much as vigorous as the first one had been. So I kept feeding them throughout the morning and early afternoon.

If I didn’t have other things to do, I could watch these all day. I hope that if I can keep feeding them this much they will regrow their dropped hydranths. Although I’m not sure how realistic it is to think that I can go through this routine every day. And do I really need a few dozen more mouths to feed on a regular basis? I seem to accumulate animals like other women accumulate shoes. On the other hand, I don’t expect the Ectopleura colonies to last long in the lab so even my “forever” relationship with these particular animals will likely be over in a week or so. I can probably keep up this level of effort for that long.

These ARE the droids I’m looking for

Posted on by Allison J. Gong

Tomorrow my students will be examining cnidarian diversity in lab, so early this morning I went to the harbor to collect hydroids. Or ‘droids, as I refer to them. These are not the droids of Star Wars fame, such as C-3PO and R2D2, but rather colonial cnidarians. As such, they are made up of many iterated units (called zooids) connected by a shared gastrovascular cavity (GVC), or gut. Despite how weird it seems to most people, this sort of colonial lifestyle is not uncommon among marine invertebrates; it occurs in several other taxa as well, most notably the Anthozoa (sea amenones, corals, and others), Bryozoa (bryozoans such as Membranipora), and Urochordata (sea squirts).

On my various trips to the harbor over the past few months I’ve been keeping an eye out for ‘droids, as I knew I’d need them. The one species I was glad to see getting established this summer is called Ectopleura crocea; it is one of the non-native members of the fouling community that shows up in harbors all along the California coast. It is a most beautiful animal, and quite conspicuous when it is present. This year I’ve seen it growing lustily on the docks, mussels, and any manmade object that has been marinating in the water for a while.

In situ it looks like this:

The hydroid Ectopleura crocea, at the Santa Cruz Yacht Harbor 19 October 2015 © Allison J. Gong
The hydroid Ectopleura crocea, at the Santa Cruz Yacht Harbor
19 October 2015
© Allison J. Gong

The stalks in this particular colony are 3.5-4 cm long. Each one of those tufts at the end of a stalk is a hydranth, the part of the zooid that bears the feeding tentacles and mouth. Hydroids are cnidarians and thus have stinging cells along their tentacles, which form a ring surrounding the mouth.

Ectopleura hydranths actually have two concentric rings of tentacles, with the mouth in the middle of the smaller ring. Between the tentacle rings there is a sort of empty space that is filled with reproductive structures called gonophores when the colony is preparing for sexual reproduction. In some hydroids gonophores release medusae, but in Ectopleura they release gametes. A given colony is either male or female, and any one of the hydranths can become reproductive and develop gonophores.

Hydroids are definitely animals whose beauty is better appreciated when observed under a microscope:

Hydranth of Ectopleura crocea 19 October 2015 © Allison J. Gong
Hydranth of Ectopleura crocea
19 October 2015
© Allison J. Gong

In the colonies of E. crocea that I’ve observed before, mature male gonophores are a solid white and female gonophores are pinkish. I collected three clumps of Ectopleura today, and none of the gonophores are mature. You can see why the common name for this animal is “pink mouth hydroid,” as the mouth is borne on a pink tubular structure called a hypostome.

I’ve tried multiple times to grow this animal in the lab. There are some experiments on resource sharing in hydroids that I’ve been wanting to do for years but haven’t yet found the right species to work with. In captivity Ectopleura eats well, then after several days all the hydranths drop off and the colonies die. I’ve never had success getting them to regrow their hydranths, either. So I bring them in for short periods and observe them up close while I can.

Off with the old, Case B

Posted on by Allison J. Gong

ORGANISM OF THE MONTH: Pugettia producta, the kelp crab

For a few months now, I’ve had a pet kelp crab running around in one of my seawater tables. I don’t remember where I collected it, or even whether or not I collected it at all; quite often crabs and other animals arrive as hitch-hikers on kelp that we bring into the lab to feed urchins, and I end up with many cool critters in my care that way. However she got here, this crab has been rather a pain in the butt during her stay with me. For at least a couple of weeks she got stuck in the drain of the table and would not come out despite three experienced marine biologists (including yours truly) trying to persuade her by altering water flow and offering food bribes. Then she disappeared from the table drain and I assumed that she had gone all the way through to the floor drain, where she could live quite happily for all eternity. Then she suddenly showed up again in one of my urchin baskets. When she came back up from the drain and how long she’d been hiding, I’ll never know.

Wondering why I keep referring to this crab as “she”? It’s because I know for certain that she’s a female. Here’s the secret to how you can determine the sex of brachyuran crabs (most of the common crabs: kelp crabs, shore crabs, rock crabs, even Dungeness crabs): You look at the shape of the abdomen, which is curved forward on the underside of the body. See here:

Abdomen of female Pugettia producta. 16 October 2015. © Allison J. Gong
Abdomen of female kelp crab (Pugettia producta)
16 October 2015
© Allison J. Gong

The abdomen is the broad flat upside-down-U-shaped panel that covers about half the width of the ventral surface. Female crabs brood their embryos under the abdomen, hence the broad shape. Male crabs of the same species have a much narrower, pointed abdomen.

Since her escapade with the drain the crab has been more, shall we say, co-operative. She’s still free to scurry around at will in the table, but I haven’t found her doing anything objectionable such as tormenting urchins or trying to get down the drain again. She has also been eating well.

Until this past week, that is. On Monday she accepted a piece of food but then abandoned it without even tasting it. On Wednesday she fled from the food, which I took to mean that she was getting ready to molt. Like all arthropods, crustaceans molt their exoskeletons every so often. The decapod crustaceans I’m most familiar with tend to off their feed for a few days before molting, and usually the actual shedding of the exoskeleton occurs at night. Then we show up the next day and voilà! like magic there’s a new, bigger crab in the table.

Ms. Kelp Crab stopped eating on Monday of this week. Today (Friday) I didn’t get to the lab until about noon, and one thing I noticed in the table was an empty carapace. Sure enough, she had molted. It took a little hunting to find the crab herself, but she wasn’t really hiding and her new exoskeleton had already hardened. I’m pretty sure she’ll eat on Monday.

Kelp crab (Pugettia producta) and carapace of its molted exoskeleton. 16 October 2015 © Allison J. Gong
Kelp crab (Pugettia producta) and carapace of her molted exoskeleton
16 October 2015
© Allison J. Gong

Living in a rigid exoskeleton means that a crustacean can increase in body size only in the time period between when an old exoskeleton is shed and the new one hardens up. I’m always curious about exactly how much crabs grow when they molt. So today I measured the crab and her old carapace at the same place, halfway between the two points on the lateral edges of the carapace. Huzzah for empirical data! The old carapace measured 27.6mm across, and the new one 33.8mm, for an increase in width of 6.2mm or 22.5%. Mind you, this is simply the increase in one linear dimension of the crab’s body. To obtain a more accurate measurement of body size increase, I’d have to have weighed the crab immediately before her molt and after it. Still, it does give an estimation of how much bigger a body part can get when a crab molts.

Cuteness strikes again!

Posted on by Allison J. Gong

That cute little Melibe I found last week is still alive, and still super cute. It lost one of the two large cerata on its back the second day I had it, and I wasn’t sure it would be able to survive long without it, but it has hung in there and started growing a replacement. This afternoon it was crawling on the underside of the surface tension in the bowl:

Melibe leonina crawling on underside of surface tension. 2 October 2015 © Allison J. Gong
Melibe leonina crawling on underside of surface tension.
2 October 2015
© Allison J. Gong

It is extremely difficult photographing transparent animals; this is the best shot I got. You are looking at the animal’s ventral surfaces. It is using its elongate foot to stick to the surface, and the rest of the body is suspended from the foot. The oral hood is wide open and you can see the little blue spots at the base of each tentacle.

The best news is that the tiny Melibe has learned how to eat! The first couple of days I offered it live brine shrimp nauplii, and the Melibe didn’t seem to like the thrashing of the nauplii. It cowered and shrank instead of trying to eat them. Then it occurred to me to mush up the nauplii first, so they wouldn’t be so active. I also thought that the Melibe might be able to eat the mush itself. Aha, success! Except that I wasn’t able to capture any video or photos then.

Today, though, the Melibe did this, while I had the camera all set up and ready to go:

Instead of cringing from the nauplii, today the Melibe was actively going after them. In this video it encloses its oral hood around a handful of nauplii and collapses the hood, forcing the nauplii into its mouth. You can actually see the nauplii stop struggling as they are ingested.

I think the Melibe is growing, too. I’ll have time to measure it on Monday.

Cuteness warning: High alert!

Posted on by Allison J. Gong

This morning I was doing some routine cleaning of animal-containing dishes at the marine lab when I noticed a little blob of snot on the outside of the bowl I was working on. Normally I just wipe off blobs like that, but something about this one caught my attention in a different way and I paused to take a closer look at it. What I saw made me glad I hadn’t given it the old Kim-Wipe™ treatment.

It was this:

Very small juvenile nudibranch (Melibe leonina). 23 September 2015 © Allison J. Gong
Very small juvenile nudibranch (Melibe leonina).
23 September 2015
© Allison J. Gong

This little 3mm blob of cuteness is the tiniest Melibe I’ve ever seen. Melibe is one of my favorite creatures of all time. It’s an entertaining animal that has unfathomable amounts of charm. Unlike most other nudibranchs, which prey on other animals (typically cnidarians, sponges, or bryozoans), Melibe is a filter feeder. It sweeps its large oral hood, visible to the right, through the water to capture plankton. The flat large-ish structures projecting from the animal’s back like wings are cerata, of which there will eventually 4-5 pairs when the slug reaches adult size. The cerata function as gas exchange surfaces; they also contain extensions of the digestive system. When a Melibe is mishandled or stressed, it drops cerata, which can then be regenerated.

Melibe is the most animated of slugs. I dropped a few brine shrimp nauplii on this little guy to see if it would be able to catch them. Unfortunately it looked more like the nauplii were ganging up on the Melibe than the other way around. However, I know from experience that even larger Melibe take a while to figure out how to eat brine shrimp.

But isn’t that the cutest slug you’ve ever seen? It has tiny bright blue dots on its body! Those two little flaps on the top surface of the oral hood are rhinophores. I know they look like ears, but they are chemosensory rather than auditory organs.

And look how fast this little nudibranch can crawl! Remember, it’s only 3mm long, and it’s making pretty good progress getting to the corner of the bowl.

When dislodged from whatever it’s crawling on, Melibe can swim. I thought this one would attach itself to the underside of the surface tension, as they often do, but it thrashed for quite a while before sort of accidentally finding the bottom of the dish again.

And do you know what the best thing about Melibe is? It smells like watermelon. I kid you not. If you touch a Melibe, your finger will smell like watermelon Jolly Ranchers. How could an animal possibly be any cooler than that?

Happy as a . . .

Posted on by Allison J. Gong

. . . clam, right? Yes, except in this case the bivalve is not a clam, but a scallop. I was out at the harbor with Brenna again this morning, looking for molluscs for tomorrow’s molluscan diversity lab. Brenna was hunting for slugs, of course, and had drawn up a rope that had been hanging in the water for god knows how long. Neglected ropes like this are the stuff of dreams for people like Brenna and me, as all sorts of animals recruit to and colonize them. Hauling one up is like going on a treasure hunt.

Two of the animals that had attached to the rope were small kelp scallops, Leptopecten latiauratus. The smaller of the two was about the size of my thumbnail and the larger was about 1.5 times that size. Their shell patterns are very beautiful:

The larger rock scallop (Chlamys hastata) collected at the Santa Cruz Yacht Harbor. 14 September 2015 © Allison J. Gong
The larger kelp scallop (Leptopecten latiauratus) collected at the Santa Cruz Yacht Harbor.
14 September 2015
© Allison J. Gong

The smaller rock scallop (Chlamys hastata) collected at the Santa Cruz Yacht Harbor. 14 September 2015 © Allison J. Gong
The smaller kelp scallop (Leptopecten latiauratus) collected at the Santa Cruz Yacht Harbor.
14 September 2015
© Allison J. Gong

But really, you don’t get a feel for how much fun these animals are until you watch them. Scallops are the most animated of the marine bivalves. They have eyes and sensory tentacles along the ventral edge of the mantle, and react strongly to stimuli. They can clap their valves together so quickly that they actually swim. I wasn’t able to make either of mine swim, but did get to watch them for a while.

The whitish object waving around on the left side of the frame is the scallop’s foot. Rock scallops are not permanently attached to surfaces (if they were, they wouldn’t be able to swim!) but they do use the foot to stick. If they find a spot they like, they try to wedge the dorsal, hinged area of the shell into a crevice.

Just like you and me, scallops have bilateral symmetry, complete with left and right sides. Unlike you and me, however, their bodies are laterally flattened and entirely enclosed between the left and right shells. The only parts of the body that extend from between the shells are the foot and the sensory structures on the mantle edge. Leptopecten has many long filament-like sensory tentacles, and brilliant blue eyes.

I thought I’d provoke a reaction by passing my finger over the animal and casting a shadow over it. Nada. But then it closed its shells a couple of times for no reason that I could discern. However, as my graduate advisor Todd Newberry used to say, The Animal Is Always Right™, and what doesn’t seem like anything to me could very well be a threat to a scallop.

And by the way, I did also collect a few slugs and a chiton for tomorrow’s lab. The highlight for me, though, was the scallops. I hope my students are as captivated by these little bivalves as I was!

Off with the old, into the new

Posted on by Allison J. Gong

The Seymour Marine Discovery Center, where I spend some time hanging out several days a week, has a spiny lobster (Panulirus interruptus) on exhibit. While the lobster doesn’t have an official name, for obvious reasons the aquarists call it Fluffy. We don’t know if Fluffy is male or female, but for convenience sake we’ve been referring to it as ‘he’ which may or may not be sexist, depending on one’s point of view. Fluffy came to the Seymour Center as a full-grown adult in September (I think) of 2012 and has molted every year close to the anniversary of his arrival.

Fluffy, the spiny lobster (Panulirus interruptus) on exhibit at the Seymour Marine Discovery Center. 7 September 2015 © Allison J. Gong
Fluffy, the spiny lobster (Panulirus interruptus) on exhibit at the Seymour Marine Discovery Center.
7 September 2015
© Allison J. Gong

Fluffy’s latest molt occurred some time between Saturday afternoon and this morning, probably in the dark of night. The molt remains in the tank, to show visitors what happened.

Spiny lobster (Panulirus interruptus) on the right and its molt. 7 September 2015 © Allison J. Gong
Spiny lobster (Panulirus interruptus) on the right and its molt on the left.
7 September 2015
© Allison J. Gong

Being encased in a rigid exoskeleton, all arthropods grow in stepwise fashion, increasing in size only during that brief period between when the old exoskeleton has been shed and the new one has hardened. Once they reach full adult size they may continue to molt yearly, but no longer grow. Fluffy’s exoskeleton may be hard by now, and to the naked eye he doesn’t look any larger than he was before. Then again, if he was already full-grown when he came here, I wouldn’t expect him to grow much, if at all.

When crabs and lobsters molt, the old exoskeleton splits apart at the junction between the carapace and abdomen. The animal slips out backwards through the split, leaving the entire covering of its body behind. Before molting the lobster’s epidermis would have resorbed some of the minerals from the old cuticle, and what is left behind is much thinner and more fragile than it was when the animal was wearing it.

Molted exoskeleton of a spiny lobster (Panulirus interruptus). 7 September 2015 © Allison J. Gong
Molted exoskeleton of a spiny lobster (Panulirus interruptus).
7 September 2015
© Allison J. Gong

In the photo above you can see the split between the carapace and abdomen. I think it’s amazing how the legs, eye stalks, and antennae can slip out of the old cuticle without being broken or damaged. However, until the new exoskeleton has fully hardened the animal is vulnerable and usually hides out for a few days. Fluffy may not eat until tomorrow or the next day. One interesting note. A lobster’s gills, being external structures, are covered by a thin layer of cuticle and are molted along with everything else. If you come across a recent crab molt, lift up the carapace and you might be able to see where the gills are located. How cool is that?

A series of unfortunate events

Posted on by Allison J. Gong

Now is not a good time to be a sea star in my care. Although to be honest, I doubt these animals would be better off in anybody else’s care, either. And what’s going on today isn’t so much a series of unfortunate events as a trio of additional episodes in the two-year serial catastrophe that we call sea star wasting syndrome (SSWS).

Episode 1: My third Leptasterias star finally bit the dust today, a full week after the first one tore itself into pieces. Yesterday I was teaching all day and didn’t have time to take pictures when I checked on things at the lab, but the star was intact. Today, not so much:

Leptasterias sp. star exploded due to SSWS. 4 September 2015 © Allison J. Gong
Leptasterias sp. star exploded due to SSWS.
4 September 2015
© Allison J. Gong

On Monday, four days ago, the star had a small lesion on the aboral surface of its central disc. It was crawling around and aside from the lesion appeared healthy. While this individual survived longer than the other two, the progression of SSWS from small lesion to total dismemberment is surprisingly rapid. I shouldn’t be surprised, as I’ve watched SSWS take apparently healthy Pisaster ochraceus stars and turn them into piles of rotting disembodied arms in a single day. That was almost exactly two years ago. Maybe it’s something about the Labor Day holiday.

Episode 2: Since I lost two of my bat stars (Patiria miniata) to SSWS back in July, I’ve been keeping an eye on the five that remain. They seemed to be doing fine until this week, when I noticed that one of them had developed a lesion. It was a very small superficial lesion on Monday but now it has grown both larger and deeper.

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

Here’s a brief note about sea star anatomy. The small inter-radial clean-edged pale orange structure located at 6 o’clock is not a lesion. That is the animal’s madreporite, the ossicle through which water passes in and out of the water vascular system. The madreporite of Patiria tends to be pretty conspicuous; in other species it can be more difficult to find.

The lesion is the larger, paler, fluffier bit that doesn’t have clean edges. It’s an open wound, and the white fluffy stuff is the star’s soft tissue. Today the wound measures about 1 cm across its widest dimension:

Lesion on aboral surface of Patiria miniata. 4 September 2015 © Allison J. Gong
Lesion on aboral surface of Patiria miniata.
4 September 2015
© Allison J. Gong

I’ll keep checking on this star and see how quickly the lesion grows.

Episode 3: Scott and I have had to accept that we aren’t having much luck growing up our tiny Pisaster stars. This afternoon we counted 16 of the 0.5mm orange dots that are juvenile stars. We consolidated 12 of them into a single jar and kept the other four in a bowl with a piece of mussel shell. We have failed to determine what it is they eat when they’re this small, unless it’s more than sheer luck that the four with the mussel shell haven’t experienced any mortality in two weeks. And yes, we will continue to change the water in the jar and the bowl twice a week.

For broadcast spawners such as Pisaster ochraceus, which shed gametes into the water, reproductive success is all about numbers–numbers of spawning individuals in a population as well as numbers of gametes produced. In our experiment the numbers just weren’t working in our favor: (1) we got usable quantities of gametes from only two females and two males; (2) fertilization success was pretty low for both crosses (Purple x Purple and Orange x Orange); (3) all embryos for the Orange x Orange cross died in the early developmental stages; and (4) settlement and metamorphosis success was low for the Purple x Purple cross survivors. And now we’re down to 16 stars. By this time next week we may be down to zero stars, although those four on the mussel shell might still be hanging on.

We knew going in that the crux of the problem would be feeding the juveniles; I was reasonably certain that we’d be able to get through the larval stages successfully. And this is indeed what has been the case. Right now I feel more than a little disheartened even though the result we got (i.e., we can’t get the damn things to eat once they metamorphose) is far from unexpected. Fortunately it will be months before our brood stock can be spawned again so I have lots of time to decide if it would be worthwhile to try the experiment again. I will need to come up with some new ideas of what to feed the juveniles.