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1

This spring and summer the local beaches have at times been covered by what appear to be small, desiccated, blue or white potato chips. They would typically be seen in windrows at and just below the high-tide line, or blown into piles. The most recently washed up ones are a dark blue-violet color, while the ones that have been on the beach for more than a day or two are faded to white.

Windrows of Velella velella (by-the-wind sailor) washed up on the beach at Point Piños, 9 May 2015. © Allison J. Gong
Windrows of fresh Velella velella (by-the-wind sailor) and algal detritus washed up on the beach at Point Piños, 9 May 2015.
© Allison J. Gong
Desiccated Velella velella on the beach at Franklin Point, 22 April 2015. © Allison J. Gong
Desiccated Velella velella on the beach at Franklin Point, 22 April 2015.
© Allison J. Gong

These animals are Velella velella, commonly called by-the-wind sailors. Taxonomically they are in the Class Hydrozoa of the Phylum Cnidaria. Other members of this class are the colonial hydroids and siphonophores (such as the Portuguese man-o'-war, Physalia) as well as the freshwater hydras that you may have played around with in high school. Technically speaking, Velella isn't a jellyfish. Actually, if we want to get uber-technical about it, there's no such thing as a jellyfish at all; or if there is, it's a vertebrate (i.e., some kind of actual fish) rather than a cnidarian. Most of the gelatinous creatures that people generally refer to as "jellyfish" are in fact the medusae of cnidarians.

That said, Velella is a special kind of hydrozoan. Its body consists of an oblong disc, 3-10 cm long, with tentacles and such hanging down and a sail sticking up. The little sail catches the wind that propels the animal:

Single Velella velella washed up on beach at Franklin Point, 22 April 2015. © Allison J. Gong
Single Velella velella washed up on beach at Franklin Point, 22 April 2015.
© Allison J. Gong

How do so many of these animals end up on the beach? The answer is that they float on the surface of the ocean and are at the mercy of the winds, hence their common name. This is an extremely specialized habitat called the neuston. Organisms living here have to be adapted to both aerial and marine factors. In fact, the blue pigment in these animals is thought to act as a sunscreen, reflecting the blue (and probably UV) wavelengths and protecting the underlying cells. We all know that UV radiation damages DNA, right? That's why we wear sun protection. Other cnidarian inhabitants of the neuston are things like Physalia and Porpita porpita (blue buttons), which are also blue in color. A former boss of mine used to say that for every hydroid there's a nudibranch that lives on it, eats it, and looks just like it. Porpita isn't exactly a hydroid, but it does have a predatory nudibranch, Glaucus atlanticus, which is (of course) blue-purple! Glaucus eats Velella, too.

Porpita porpita (left) and its predator, the nudibranch Glaucus atlanticus. Diameter of P. porpita approx. 2 cm.
Porpita porpita (left) and its predator, the nudibranch Glaucus atlanticus. Diameter of P. porpita approx. 2 cm.

 

 

 

 

 

 

 

 

The Monterey Bay Aquarium Research Institute (MBARI) has, of course, one of the best video explanations of what Velella is all about. I certainly can't do any better, so you should watch this:

By the way, MBARI's YouTube channel is like marine biology and oceanography porn. Just sayin'. If you have some time to kill on the Internet, you could certainly do worse than to spend it there!

Today the Pisaster larvae that Scott and I are following are a week old. Happy birthday, little dudes! Yesterday we did the twice-weekly water change and looked at them. They're getting big fast since we started feeding them on Saturday when their mouths finally broke through. At this stage they are sort of jellybean-shaped and extremely flexible--they don't have the calcified skeletal rods that sea urchin larvae have so they bend and flex quite a lot. They are also beautifully transparent, which allows us to see their guts in fine detail. We can even watch them swallow food cells!

Front view of Pisaster ochraceus bipinnaria larva, age 7 days, 8 June 2015. © Allison J. Gong
Front (ventral) view of Pisaster ochraceus bipinnaria larva, age 7 days, 8 June 2015.
© Allison J. Gong

In profile view you can see that the larvae are shaped sort of like fat C's. Here's a side view of a different individual:

Right side view of bipinnaria larva of Pisaster ochraceus, age 7 days. © Allison J. Gong
Right side view of Pisaster ochraceus bipinnaria larva, age 7 days.
© Allison J. Gong

In the short term (over the next couple of weeks or so) the larvae will continue to get longer. Their guts won't change much, but their coelomic systems will develop and become more complex. I'll try to capture that in photos and drawings to share with you.

 

3

This morning I went on a solo trip to one of my favorite intertidal sites up the coast a bit. I've been busy with stuff at the marine lab and my house is a construction zone this summer so it was really nice being alone in nature for a couple of hours before most people had gotten out of bed.

I didn't find what I was looking for but did see some great stuff that I wasn't looking for, which is just as rewarding.

The approach to the beach over the dunes is always spectacular even on a gloomy morning. I find this color palette very soothing.

The hike over the dunes, 5 June 2015. © Allison J. Gong
The hike over the dunes, 5 June 2015.
© Allison J. Gong

The site itself is rocky with a sandy bottom. Depending on the severity of recent storm action there can be more or less sand. Winter storms wash sand away, while in the summer the sand tends to accumulate and can bury the rocks to surprising depths.

Surfgrass bed (Phyllospadix sp.) and rocks at Franklin Point, 5 June 2015. © Allison J. Gong
Surfgrass bed (Phyllospadix sp.) and rocks at Franklin Point, 5 June 2015.
© Allison J. Gong

It may be an optical illusion, but when I'm scrunched down in amongst the rocks it appears that the waves are breaking at heights quite a bit above my head. Most of the water's force is dissipated as the waves wash over the rocks, and unless I've wandered out too far, by the time it gets to me all I need to worry about is whether the surge will overtop my boots. Which has indeed happened and makes for a cold squelchy morning.


And now for some happy snaps!

A small mid-intertidal pool at Franklin Point, 5 June 2015. © Allison J. Gong
An example of intertidal biodiversity at Franklin Point. The most conspicuous organisms are Ulva (sea lettuce), coralline algae (the pink stuff), small acorn barnacles, the tube-dwelling worm Phragmatopoma californica, and small anemones in the genus Anthopleura. 5 June 2015.
© Allison J. Gong
I love my hip boots!  © Allison J. Gong
I love my hip boots!
© Allison J. Gong
Pagurus hirsutiusculus hermit crab in shell of the snail Olivella biplicata, 5 June 2015. © Allison J. Gong
Pagurus hirsutiusculus hermit crab in shell of the snail Olivella biplicata, 5 June 2015.
© Allison J. Gong
A beautifully camouflaged kelp crab (Pugettia producta) hiding in plain sight, 5 June 2015. © Allison J. Gong
A beautifully camouflaged kelp crab (Pugettia producta) hiding in plain sight, 5 June 2015.
© Allison J. Gong

Because, really, doesn't everybody have a favorite red alga? This is mine. It presses gorgeously and is so damn beautiful!

Erythrophyllum delesserioides, 5 June 2015. © Allison J. Gong
Erythrophyllum delesserioides, 5 June 2015.
© Allison J. Gong

At one point I saw a worm-like thing thrashing around in a shallow pool. Turns out it was a polychaete worm, probably in the genus Nereis, doing epic battle with a predatory nemertean worm (Paranemertes peregrina). By the time I figured out what was going on and stuck my camera in the water the interaction had more of less come to an end. The polychaete did get away without apparent damage, but it was moving pretty slowly afterward. In this video Nereis is the segmented worm that's doing all the wiggling, and Paranemertes is the purple and beige unsegmented worm that you can sort of make out in the top of the frame. I wish I had been swifter on the uptake with the camera.


And the pièce de résistance for this trip:  A little sea hare! This guy was so small (about 2.5 cm long) that at first I thought it was a clump of red algae. Then I saw the little rhinophores (those ear-like projections that give them their common name) and recognized it as a sea hare. Amazingly cute!

A little sea hare (Aplysia sp.), 5 June 2015. © Allison J. Gong
A little sea hare (Aplysia sp.), 5 June 2015.
© Allison J. Gong

I was lucky enough to capture some video of this critter crawling around.

Aside from the rhinophores it doesn't look hare-like at all, does it? I wonder about common names sometimes.

All in all, it was a great morning. An early morning low tide is the best reason I can think of to crawl out of bed at 04:30!

It's becoming quite clear that I don't have to worry about having too many sea star larvae to deal with. While the embryos from my F1 x M1 (Purple x Purple) cross had hatched this morning, nothing from the F2 x M1 (Orange x Purple) cross looked promising. I'm about ready to write off these guys and dump them all down the drain, but will give them until tomorrow to pull themselves together and do something that doesn't look all wonky.

In the meantime, it's really fun looking at the good embryos from the F1 x M1 mating. They hatched out of their fertilization envelopes and have become elongated, sort of like stubby Tylenol caplets. This elongation defines a functional anterior-posterior axis, and the animal swims with its anterior end forward.

Gastrulating embryo of Pisaster ochraceus, 4 June 2015. © Allison J. Gong
Gastrulating embryo of Pisaster ochraceus, 4 June 2015.
© Allison J. Gong

Gastrulation is the process of forming the first larval gut, or archenteron. Remember how yesterday the embryo was a hollow ball of cells called a blastula? In these echinoderms gastrulation is simply an invagination into the blastula. Imagine poking your finger into an inflated balloon:  The balloon is the blastula and your finger forms an invagination, or channel, through it. In embryos, gastrulation begins at a site on the blastula called the blastopore; this is where you'd stick your finger into the balloon in our analogy.

Most animal guts have two openings, a mouth and an anus. You understand what happens at each of those openings. The archenteron is a gut, one of whose openings is the blastopore. The fate of said blastopore is to be either the mouth end or the anus end of the archenteron. In echinoderms, the major invertebrate phylum that makes up a larger grouping of animals called the deuterostomes, the blastopore becomes the anus, with the mouth breaking through as the process of gastrulation finishes. And lest you think that possessing an anus before a mouth is somehow less evolved than the reverse would be, you might be interested in knowing that we humans are also deuterostomes. That's right, each of you reading this blog, as well as the one who writes it, built an anus first and a mouth second.

These sea star embryos swim really fast! I had to squash them under a cover slip to snap some halfway decent pictures, and even then it wasn't easy to slow them down or chase them around on the slide. You can get a feel for how fast they can move in this short video clip:

The archenteron appears to wobble because it doesn't go straight through from the blastopore to the apex of the embryo. The mouth will break through along one of the sides, resulting in a curved gut. I suspect that when I look at the embryos tomorrow they will have graduated to the status of larvae, with complete guts. Then I get to start feeding them and watching them grow.

I've been fielding questions about my recent sea star spawning work from people I've shared this blog with, which is a lot of fun! To streamline things and make the info available to anybody who might be following, I decided to put together a very brief FAQ-like post to address the most recent questions.

Question:  Can you watch the eggs divide in real time?

In a time-lapse sense you can watch cleavage divisions occur, but not in real time. What I can do is set up a slide on the microscope and leave it there for a while. The gradually warming temperature speeds up development to the point that I can sort of see the division in real time. Of course, the danger is that the embryo will cook on the slide. I generally figure that once I've pipetted some embryos onto a slide and dropped a cover slip on top of them, they're goners (it's not really possible to remove the cover slip without damaging the cells underneath it) so I feel marginally less bad about sacrificing a few to the gods of observation.

Questions:  I’m fairly certain that the stars can go back to the sea, but are you able to keep their eggs with them, too? How difficult is that transport?

Actually, my scientific collecting permit specifically states that I'm not allowed to return animals to the wild. If I needed to, I could apply for additional permits but it has never been necessary for the work I do. Surplus eggs and larvae, therefore, are discharged into the seawater outflow at the lab and do return to the ocean but the parents remain in my care.

Question:  Are orange and purple stars usually able to cross with each other?

As far as anyone has been able to determine, the color of stars has zero effect on whether two individuals' gametes are able to do the nasty together. The sea stars that I'm working with--Pisaster ochraceus, the ochre star--are broadcast spawners, meaning that each individual spews his/her gametes into the water, where fertilization and development occur. The stars are also synchronous spawners, meaning that if one individual in an area begins spawning other stars in the immediate vicinity will also spawn. After all, it does take two to tango, and to spawn while nobody else does is a tremendous waste of energy.

So yes, a purple star and an orange star should be able to mate without any problems... at least not any problems due to the parents' colors.

Question:  If so, what color do they end up being, statstically?

This is a very interesting question. Two of my colleagues are going to spawn Patiria miniata (bat stars) next week to address this. Their plans are to cross a Blue female with an Orange male, an Orange female with a Blue male, and both pure-color matings. They did a preliminary version of this experiment a couple of years ago but didn't end up with enough juveniles at a size that color could be ascertained; thus they couldn't calculate any statistically meaningful color ratios.

Questions:  Do you suppose that the wasting disease could be now in the genetic makeup? Any thoughts (unofficial of course) about this?

My thought is sort of the opposite, actually. The animals that we brought in from the field are all survivors of SSWS; if anything, I'd expect them to be resistant to whatever causes the plague, and to (hopefully) pass on this resistance to their offspring. Of course, there's no way of knowing if and how exposure to SSWS affects the quality of the gametes. It's quite possible that these survivors are less fit after the SSWS outbreak than they were before.

Question:  Purple Male with Purple Female developed well and purple Male with Orange female didn’t…some sort of incompatibility?

Well, given what I saw today the Orange (female) x Purple (male) cross almost certainly did not work. Fertilization occurred, but almost none of the embryos had any indication of normal development. Since we know the Purple male was able to mate successfully with the Purple female, we can infer that his sperm were fine. It could be that there was something going on with the Orange female's eggs; there were a lot of them, but maybe their quality just wasn't very good. Or perhaps we somehow mistreated and wrecked them the other day.

Any other questions? Use the Comments section to ask them, and I'll address them in a future post.

Wow, they weren't kidding about "early developmental asynchrony" in sea stars! This morning I looked at the embryos that I had started almost 24 hours earlier, and noticed two things right off the bat:

Thing #1:  Within the F1 x M1 (Purple female x Purple male) mating , developmental rates among full siblings were all over the map. Some embryos had progressed to the blastula stage, which is essentially a hollow ball of ciliated cells, while others were still in the early cleavage stages and rather a lot hadn't divided at all. In fact, with 24 hours of hindsight I can see that several of these eggs had not even been fertilized.

Embryos of Pisaster ochraceus, age 24 hrs. 3 June 2015. © Allison J. Gong
Embryos of Pisaster ochraceus, age 24 hrs. 3 June 2015.
© Allison J. Gong

My first reaction upon looking into the microscope and seeing all these assorted blobs was, "Oh, crap." But then I looked more closely at some of the embryos and realized that they had become blastulae!

Here's a picture of a blastula. This embryo is freely swimming inside its fertilization envelope, although it doesn't have a lot of space (remember that narrow perivitelline space from yesterday? that's all the elbow room it has). The hollow space in the center of the embryo is the blastocoel 'sprout cavity.' Given that the embryo hasn't grown (or even hatched) yet, it's still ~165 µm in diameter, the size of the original egg.

Blastula of Pisaster ochraceus, 3 June 2015. © Allison J. Gong
Blastula of Pisaster ochraceus, 3 June 2015.
© Allison J. Gong

The stage that precedes the blastula (a hollow ball of cells) is called a morula (a solid ball of cells). The embryo that is partially visible in the bottom of the above photo may be a morula. Imagine the following sequence of events: (1) an egg is fertilized by a sperm, forming a zygote; (2) the zygote undergoes a number of cleavage divisions, with the cells becoming more numerous and smaller in size; (3) at some stage a solid ball of small cells, the morula, is formed; (4) as cell division continues, the cells migrate toward the outside of the sphere, forming a cavity (the blastocoel) in the middle.

The blastula is a ciliated stage, and in this video clip you can see the cilia moving. I shot this video at only 100X magnification to capture as much depth of field as possible, and suggest viewing at full-screen. This should enable you to see the three-dimensional structure of the embryo, and that it is indeed a sphere.


Thing #2:  The F2 x M1 mating (Orange female X Purple male) isn't doing well at all. I looked at several slides and didn't see any embryos that were developing normally. They had all been fertilized, as I could see the fertilization envelope surrounding each egg, but most had not even divided. The ones that had divided were all strange and just plain wrong. Here, see for yourself:

24-hr embryos of Pisaster ochraceus, 3 June 2015. © Allison J. Gong
24-hr embryos of Pisaster ochraceus, 3 June 2015.
© Allison J. Gong

Many of the eggs are blurry because they're below the focal plane of the microscope. But see how many of them are undeveloped? And how, in the ones that have started dividing, the cells are disorganized and of different sizes? Typical echinoderm cleavage, as I see in echinoids (our local urchins and sand dollars) and in my other crossing of these ochre stars, results in a blastula made up of cells that are all approximately the same size. Most of these embryos, on the other hand, appear to consist of one large cell and a bunch of tiny ones.

I assume that these abnormal-looking-to-me embryos will not hatch, although I could be pleasantly surprised tomorrow. I don't yet have much of an intuition about these Pisaster ochraceus embryos, so this is a huge learning experience for me. I do expect to see hatching in the F1 x M1 cross tomorrow. Fingers crossed!

2

A recent college graduate and fellow marine lab denizen (Scott) and I are collaborating on a project to quantify growth rates in juvenile Pisaster orchraceus stars. This is one of the intertidal species whose populations in the field and in the lab were decimated by the most recent outbreak of sea star wasting syndrome (SSWS). We are interested in seeing how quickly the stars grow once they metamorphose and recruit to the benthos, and hope that the information will help researchers guesstimate the age of the little stars that are now being seen in the field. This would in turn tell us whether the little stars are survivors of SSWS or post-plague recruits. I keep seeing people refer to them as "babies," but they could very well be several years old. We just don't know, hence this study.

Large, healthy specimen of Pisaster ochraceus at Davenport Landing. 20 May 2015. © Allison J. Gong
Large, healthy specimen of Pisaster ochraceus at Davenport Landing. 20 May 2015.
© Allison J. Gong

But before we get to measure juvenile growth we have to get through larval development, which is perfectly fine by me because I'm always up for observing marine invertebrate larvae. Two weeks ago Scott and I ventured into the field in search of prospective parents. We brought back eight individuals from two different sites, making sure to leave many more in place than we took away. It was actually rather gratifying to see how many hand-sized-or-larger P. ochraceus there were. This morning we met at 07:30 to shoot up the stars with magic juice and then wait for them to spawn.

We have injected the stars (Pisaster ochraceus) and are waiting for them to spawn. 2 June 2015 © Allison J. Gong
We have injected the stars (Pisaster ochraceus) and are waiting for them to spawn. 2 June 2015.
© Allison J. Gong

It has been a while since I tried to induce spawning in Pisaster, and I had forgotten how much longer everything takes compared to the urchins. For one thing, the magic juice itself isn't the same stuff that we use on the urchins, and works by an entirely different mechanism. The stars' response to the magic juice takes 1.5-2 hours, whereas if the urchins aren't doing anything 30 minutes after getting shot up they either need another injection or simply don't have gametes to share.

However, despite my misgivings the animals spawned. Two large females gave us enormous quantities of eggs, and three more donated trivial amounts that we didn't end up using.

This purple individual is the one we designated Female 1. See the huge piles of salmon-pink eggs?

Large purple female Pisaster ochraceus, spawning. 2 June 2015 © Allison J. Gong
Large purple female Pisaster ochraceus, spawning. 2 June 2015.
© Allison J. Gong

and

Large orange female Pisaster ochraceus, spawning. 2 June 2015 © Allison J. Gong
Female 2, a large Pisaster ochraceus, spawning. 2 June 2015.
© Allison J. Gong

Although we had to wait for a male to spawn, we finally did get some sperm and fertilized the eggs at about 12:30. Another thing I had forgotten was that Pisaster eggs, when shed, are lumpy and strange. I was used to the urchin eggs, which are usually almost all beautifully spherical and small. The stars' eggs are about twice as big, at ~160 µm in diameter. The lumpiness doesn't seem to hamper the fertilization process, as you can see below.

Fertilized eggs of Pisaster ochraceus, 2 June 2015 © Allison J. Gong
Fertilized eggs of Pisaster ochraceus, 2 June 2015.
© Allison J. Gong

In this photo you can see the fertilization envelope surrounding most of the eggs. In stars the perivitelline space (the space between the egg surface and the fertilization envelope) is very narrow, which makes it difficult to see the envelope; in urchins the space is much larger, and as a result the envelope quite conspicuous. The rising of the fertilization envelope off the surface of the egg is referred to as the slow block to polyspermy, a mechanical barrier that keeps multiple sperms from penetrating any individual egg. There's also a fast block to polyspermy, but it happens on a molecular level milliseconds after a sperm makes contact with the egg surface; you can't see it happen in real time.

Cleavage in stars proceeds much more slowly than it does in urchins, too. In embryological terms, "cleavage" refers to the first several divisions of the zygote, during which the cell number increases as the cell size decreases. This inverse relationship between cell size and number logically has to occur because the embryo can't get any larger until it has a mouth and begins to feed, which won't happen for at least a couple of days. It took our zygotes about four hours to undergo the first cleavage division.

2-cell embryo of Pisaster ochraceus, 2 June 2015 © Allison J. Gong
2-cell embryo of Pisaster ochraceus, 2 June 2015.
© Allison J. Gong

I left the slide on the microscope to warm up and speed development a bit, and about 45 minutes later was rewarded with this mishmash of embryos at different stages. Nine hours after we started this whole process, there were 2-cell, 4-cell, and 8-cell embryos, as well as eggs that had not divided yet.

Embryos of Pisaster ochraceus, about four hours post-fertilization. 2 June 2015 © Allison J. Gong
Embryos of Pisaster ochraceus, about four hours post-fertilization, 2 June 2015.
© Allison J. Gong

This asynchrony in early development is another way that stars differ from urchins, and it takes some getting used to. I expect that development will become more synchronized as the embryos continue to cleave, and that hatching will occur for all of them at about the same time, probably before Thursday. At least it won't take another 9-hour day to see how far they've come.

 

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