Tag: marine invertebrates

Crab feed(ing)!

Posted on by Allison J. Gong

Anybody who has visited one of the sandy beaches in California has probably seen kids running around digging up mole crabs (Emerita analoga). These crabs live in the swash zone at around the depth where the waves would be breaking over your ankles, moving up and down with the tide. They are bizarre little creatures, burrowing backwards into the sand with just their eyestalks and first antennae reaching up into the water.

Although it’s called a mole crab, Emerita‘s external anatomy isn’t very similar to that of other crabs. For one thing, it doesn’t have claws. In fact, its legs are quite unlike the legs that you’d see in a typical crab. Check out Emerita‘s appendages:

External anatomy of Emerita analoga
External anatomy of Emerita analoga

The crab’s head faces to the left in this diagram. The real surprise that these little crabs hide is the nature of the second antennae. Usually the crab keeps these long, delicate antennae protected under its outer (third) pair of maxillipeds. This is why you don’t see them when you dig up a mole crab.

You do see them when the crabs are feeding. As a wave washes over the crab, it extends the second antennae and pivots them them around on ball-and-socket joints. The feathery antennae catch particles in the water, then are drawn underneath the maxillipeds so the food can be slurped off and eaten.

Here’s a top-down view of two Emerita feeding. The purple-grayish thing in the field of view is a sand dollar (Dendraster excentricus).

This side view gives a better angle of what’s going on:

I find these little crabs quite captivating. I love how they rise up when I put food into their tank.  Watching them feed always makes me smile.

Competence

Posted on by Allison J. Gong

In the parlance of invertebrate zoologists, competence is the state of development when a larva has all of the structures and energy reserves it needs to undergo metamorphosis into the juvenile form. In the case of my sea urchins, this means that they have four complete pairs of arms, each with its own skeletal rod, and a fully formed juvenile rudiment, which contains the first five tube feet of the water vascular system. A continuous ciliated band runs up and down all eight arms and provides the water current used both for swimming and feeding. The larva will have been eating well and its gut will be full of food. It will have lost the transparency it had when it was younger and will appear to be more solid-looking in the central area.

The first batch of larvae that I began culturing this season are now 42 days old. Some of these are competent, or very nearly so. Last week I isolated about a dozen of these big guys into a small dish, making it easier for me to observe them closely every day. Today they looked decidedly opaque and dumpy, and although some of them were still swimming others were heavy and tended to rest on the bottom of the dish.

Here’s a photo that I took yesterday:

41-day-old pluteus larva of Strongylocentrotus purpuratus, 2 March 2015. ©Allison J. Gong
41-day-old pluteus larva of Strongylocentrotus purpuratus, 2 March 2015.
©Allison J. Gong

General orientation: This is a ventral view. The animal swims with its arms forward, which defines the anterior portion. Thus the bottom of the cup-shaped body is the posterior. This larva measures ~900 microns along the anterior-posterior axis. Plutei have bilateral symmetry that goes all to hell during metamorphosis, from which the urchin crawls away with typical echinoderm pentaradial symmetry. This wholescale change in body organization is one of the truly amazing things about metamorphosis in these animals. It boggles my mind every time I think about it.

You can see that this pluteus has eight arms. The oblong reddish structure in the middle is the stomach, which has taken on the color of the food the animal has been eating. The strange mixed-up looking structure adjacent to the stomach on the animal’s left side is the juvenile rudiment. Focusing up and down through the rudiment shows that it contains five tube feet. After metamorphosis, the juvenile urchin will use those first five tube feet to walk around as a benthic creature, having spent all of its life up to this point as a member of the plankton.

Today I captured about 20 seconds of a larva feeding. This individual is a day older than the one in the photo above and has more of that opacity that I associate with competence.

This is a dorsal view; if you imagine that you’re looking at the animal’s back, you see that the rudiment is indeed on its left side. The larva’s ciliated band is moving a lot of water, and the little specks that you can see flying around are food cells. There wasn’t enough water in this drop for the pluteus to do any actual swimming, but at this point it’s pretty heavy and would tend to sink to the bottom.

Some time in the next several days these guys are going to start metamorphosing. I will be examining them every day; keep your fingers crossed that I catch them in the act!

 

 

Wasting leather (star)

Posted on by Allison J. Gong

Until recently I hadn’t closely observed what it looks like when a leather star (Dermasterias imbricata) succumbs to wasting syndrome. When I had the outbreak of plague in my table almost 18 months ago now, my only leather star was fine one day and decomposing the next, so I didn’t get to see what actually happened as it was dying.

(Un)fortunately, one of the leather stars at the marine lab started wasting a bit more than two weeks ago, and this time I was able to catch it at the beginning. This animal wasn’t in my care so I didn’t check on it as frequently as I would if it had been living in one of my tables, but one of the aquarists pointed it out to me when it began getting sick.

The first symptom was a lesion on the aboral surface. I say “lesion” but it’s more of an open wound.

Dermasterias imbricata with aboral lesion, 2 February 2015. ©Allison J. Gong
Dermasterias imbricata with aboral lesion, 2 February 2015.
© Allison J. Gong

You can see that the animal’s insides are exposed to the external environment. In the photo above the whitish milky-looking stuff is gonad (I’m pretty sure this animal was a male) and the beige ribbon bits are pyloric caeca, essentially branches of the stomach that extend into the arms. What typically happens along with the development of lesions like this is an overall deflating of the star as the water vascular system and other coelomic systems become increasingly compromised, and the tendency for the animal to start tearing off its arms.

Which results in this, a week later:

Wasting Dermasterias imbricata, autotomizing its arm, 9 February 2015. ©Allison J. Gong
Wasting Dermasterias imbricata, autotomizing its arm, 9 February 2015.
© Allison J. Gong

This poor animal had torn its arm off, and continued to live for a while. I find it fascinating that the lack of a centralized nervous system means that this animal literally didn’t know it was dead. It was finally declared officially dead two days later. Compared to how quickly wasting syndrome kills the forcipulates that I’ve seen (Pisaster, Pycnopodia, and Orthasterias), the leather stars take a long time to die–several days from start to finish, opposed to a matter of hours as I saw with my stars. The leathers didn’t seem to be hit as hard by the first wave of the disease outbreak, either. Is Dermasterias somehow able to fight off the infection a bit longer? It would be interesting to know, wouldn’t it?

Off to the races!

Posted on by Allison J. Gong

Yesterday I drove up the coast to Pigeon Point to do a little poking around. I had originally planned to search for little stars, survivors that had made it through the most recent outbreak of wasting syndrome. But I got distracted by other things and gave up on the stars, for now. I need to do some thinking about the best way to find tiny animals in a very complex 3-dimensional habitat.

I did spend quite a bit of time turning over rocks in tidepools. The most common critters I found were the usual suspects–porcelain crabs, limpets, snails, the odd sculpin or two, and chitons. One rock yielded a gold mine: five chitons of a species I didn’t recognize (which doesn’t mean I haven’t seen it before, just that I didn’t immediately know its name) that demonstrated a most interesting behavior.

Stenoplax heathiana, on underside of rock, 31 January 2015. Photo credit: Allison J. Gong
Stenoplax heathiana, on underside of rock, 31 January 2015.
© Allison J. Gong

I turned the rock over and watched as the chitons ran away from the exposed surface onto the other side. Yes, RAN. I’ve never seen a chiton do anything this fast. Chitons, for the most part, lead apparently inactive lives. When we do get to see them in their natural setting, at low tide, they are usually scrunched down hard on the rock waiting for the water to come back. Obviously they are much more active when covered with water, but we don’t get to see them then. In the lab, where they can be immersed all the time unless they crawl up the walls, they do wander around a bit; however, to see a chiton do much of anything requires time-lapse photography.

Don’t believe that a chiton can run? Well, get a load of this:

This is in real-time, not sped up. Watch the chiton push a limpet and the snail out of the way. Okay, I’ll grant that a limpet and a snail are not the strongest obstacles one could face when trying to flee from the light. But you can’t deny that this chiton seems to be feeling a sense of urgency.

This species, Stenoplax heathiana, spends its days buried in sand on the underside of rocks. It comes out to feed at night, not on algal scums as most chitons do, but on bits of algae that drift by and get caught between rocks. Apparently the chiton can be found exposed in the very early morning. I’m going to have to try finding some this spring when we get our morning low tides back.  Anybody want to come with me?

 

Larvae as . . . particles?

Posted on by Allison J. Gong

On another glorious afternoon low tide the other day, with the help of a former student I collected six purple urchins, Strongylocentrotus purpuratus. Given that we’re in about the middle of this species’ spawning season, I reasoned that collecting six gave me a decent chance of ending up with at least one male and one female that hadn’t spawned yet.

Yesterday, after the urchins had been in the lab for somewhat less than a whole day, I shot them up and waited. Three females began spawning almost immediately (yes!) and one male started a few minutes later. When all was said and done I ended up with four females and two males. It turns out that the largest individual, with a test diameter of almost 10 cm, was a male but didn’t spawn very much at all. I infer from this that he had already spawned in the field before I collected him.

Female (left) and male (right) spawning purple sea urchins (Strongylocentrotus purpuratus). 20 January 2015. Photo credit: Allison J. Gong
Female (left) and male (right) spawning purple sea urchins (Strongylocentrotus purpuratus), 20 January 2015.
© Allison J. Gong

At the current ambient sea water temperature of 14°C, hatching begins around 24 hours post-fertilization. Early this afternoon I checked on the beakers and they had indeed begun hatching. Sea urchins hatch at the blastula stage of development, when they are essentially a ciliated hollow ball of cells. The cilia allow the larvae to swim, but at this size they are at the mercy of even the weakest current. Thus, for the most part they act as particles, getting carried wherever the current takes them.

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. The empty space inside each embryo is called the blastocoel. 20 January 2015.
© Allison J. Gong

As the embryos hatch, they swim up to the top of the beaker, then move down towards the bottom. I call this “streaming.” At this point in our artificial culturing system the embryos are living in still water without any current, so this behavior is due primarily to their ability to swim. There is probably some interesting physics involved, but I’m not enough of a physicist to figure out what’s going on at that level. But whatever it is, it’s a really cool behavior to watch:

Rather mesmerizing, isn’t it? Each of those tiny orange dots is an individual embryo. Once the embryos hit the water column I pour them off into larger jars and begin stirring them. Right now they’re small enough to swim on their own, but once they start feeding and growing they get heavier and would sink to the bottom without some current to keep them suspended. The contraption we use to stir jars of larvae is a manifold of paddles connected to a motor that moves the paddles back and forth, creating the right amount of current to keep the larvae from settling on the bottom without getting beat up by the turbulence.

Here’s the paddle table in action. It’s a noisy SOB.

For now the embryos just hang out in the jars and get stirred. Their first gut, the archenteron, will be visible tomorrow and the larvae will be able to eat on Friday. Stay tuned!

A whole lotta pink

Posted on by Allison J. Gong

The temperate rocky intertidal is about as colorful a natural place as I’ve seen. Much of the color comes from algae, and in the spring and early summer the eye can be overwhelmed by the emerald greenness of the overall landscape due to Phyllospadix (surf grass, a true flowering plant) and Ulva (sea lettuce, an alga). However, close observation of any tidepool reveals that the animals themselves, as well as smaller algal species, are at least as colorful as the more conspicuous surf grass and sea lettuce.

Take the color pink, for example. Not one of my personal favorites, but it is very striking and sort of in-your-face in the tidepools. Maybe that’s because it contrasts so strongly with the green of the surf grass. In any case, coralline algae contribute most of the pink on a larger scale. These algae grow both as encrusting sheets and as upright branching forms. They have calcium carbonate in their cell walls, giving them a crunchy texture that is unlike that of other algae. They grow both on large stationary rocks and smaller, easily tumbled and turned over rocks.

A typical coralline “wall” looks like this:

Coralline rock with critters, 18 January 2015. Photo credit: Allison J. Gong
Coralline rock with critters, 18 January 2015.
© Allison J. Gong

Mind you, this “wall” is a bit larger than my outspread hand. The irregular pink blotches are the coralline algae. Near the center of the photo is a chiton of the genus Tonicella; its pink color comes from its diet, which is the same coralline alga on which it lives. The most conspicuous non-pink items on this particular bit of rock are the amorphous colonial sea squirt (shiny beige snot-like stuff) and the white barnacles on the right.

What really caught my eye today were the sea slugs Okenia rosacea, known commonly as the Hopkins’ Rose nudibranch. Now, it is very easy to love the nudibranchs because they are undeniably beautiful. The fact of the matter is that they are predators, and some of them eat my beloved hydroids, but that’s a matter for another post. Today I saw dozens of these bright pink blotches dotting the intertidal, both in and out of the water:

Okenia rosacea, the Hopkins' Rose nudibranch, emersed. 18 January 2015. Photo credit: Allison J. Gong
Okenia rosacea, the Hopkins’ Rose nudibranch, emersed. 18 January 2015.
© Allison J. Gong
Okenia rosacea, immersed. 18 January 2015. Photo credit: Allison J. Gong
Okenia rosacea, immersed. 18 January 2015.
© Allison J. Gong

Only when the animal is immersed can you see that it is a slug and not a pink anemone such as Epiactis prolifera, which I’ve seen in the exact shade of pink. But anemones don’t crawl around quite like this:

Whenever I see O. rosacea I automatically look for its prey, the pink bryozoan Eurystomella bilabiata. Lo and behold, I found it! The bryozoan itself is also pretty.

The bryozoan Eurystomella bilabiata, preferred prey of the nudibranch Okenia rosacea. 18 January 2015. Photo credit: Allison J. Gong
The bryozoan Eurystomella bilabiata, preferred prey of the nudibranch Okenia rosacea. 18 January 2015.
© Allison J. Gong

Can you distinguish between the coralline algae and the pink bryozoan in the photo? Is it shape or color that gives it away? If you had to explain the difference in appearance between these two pink organisms to a blind person, how would you do it?

Monsters in the making

Posted on by Allison J. Gong

Yesterday I collected three very small Pycnopodia helianthoides stars. When I brought them back to the marine lab I decided to photograph them because with stars this small I could easily distinguish between the original five arms and the new ones:

OLYMPUS DIGITAL CAMERA OLYMPUS DIGITAL CAMERA Pycnopodia juvenile

These guys began their post-larval life with the typical five arms you’d expect from an asteroid. At this stage they are pretty conspicuous because they are the largest arms. The other arms arise in the inter-radial regions between arms. For years now I’ve been wanting to watch juvenile Pycnopodia stars growing their extra arms, and it looks like I finally have my chance. I noted that these stars are all about the same size, but don’t have the same number of arms. It would be interesting to see if the rate of arm appearance and growth is related to how much food the stars have. Hmmm, that sounds like a study I should do.

And then one of the stars started running. And I mean running. Watch:

You might wonder how in the heck they can run so fast, and it’s a valid question. We can actually examine the animal’s scientific name to get an answer. “Pycnopodia” means “dense foot” and “helianthoides” means “sunflower-like.” So these guys have a lot of tube feet, and they use them to run and feed. Imagine how fast we could run if we had more than two feet and could co-ordinate them this well:

So, when these guys (gals?) grow up, they’ll be at least half a meter in diameter with 20-24 arms. With all those tube feet, they’ll be Speedy Gonzales! In fact, they will be the terror of the intertidal–big, fast, and voracious. Anything that can’t get out of their way will be eaten.

We air-breathing land mammals should be grateful that echinoderms never managed to get out of the sea. Can you imagine this monster chasing you down a dark alley, or climbing through your bedroom window?

Fouling communities

Posted on by Allison J. Gong

On 11 March 2011 a magnitude 9.0 earthquake occurred off the coast of Japan. About 14 hours later, at 11:15 a.m. local time a tsunami came through the Santa Cruz Small Craft Harbor. It sank dozens of boats and significantly damaged several of the docks. People were ordered to evacuate the area before the expected arrival of the tsunami, but of course there were those who chose to stay behind and shoot videos like this one (the real action starts at about 1:00):

 

As a result of the damage to the infrastructure of the marina itself, many of the docks have been replaced since 2011, including those that are closest to the mouth of the harbor. For several years now I have been taking marine biology students to the docks to examine the organisms growing on the undersides of the docks, and this year the biological community is finally getting interesting again. These particular organisms are described as “fouling” because they are the ones that colonize the bottoms of boats and have to be scraped off periodically. They are characterized by fast growth rates and short generation times; many of them are also colonial. The first arrivals settle onto the surface of the docks, and later arrivals can take up residence either on the docks or on their predecessors. A healthy fouling community has a rich diversity of marine invertebrates, algae, and the occasional fish. This semester’s trip to the harbor occurred a few weeks ago, and as usual the students were amazed at the amount and diversity of life on the docks. I remembered to bring the waterproof camera and snapped some shots.

This is what you see when you lie on the dock and hang your head over the edge:

OLYMPUS DIGITAL CAMERA

It’s a mosaic of color and texture, really quite beautiful. You can see that mussels are the largest organisms in this community, and in turn are substrate for a variety of other animals.

Peering a bit closer to take notice of individual animals, you start to see things like this:

A perennial favorite because of its beautiful coloring. It eats my hydroids, though, so I don't like it.
Hermissenda opalescens, a perennial favorite because of its beautiful coloring. It eats my hydroids, though, so I don’t like it.

 

One of the colonial hydroids, Plumularia sp. that grow at the harbor.
One of the colonial hydroids, Plumularia sp. that grow at the harbor. This species always grows in this pinnate form. Absolutely gorgeous under the microscope.
These small white anemones (Metridium senile) are about 3 cm tall.
These small white anemones (Metridium senile) are about 3 cm tall.
Feather duster worm, Eudistylia vancouveri, easily one of the most conspicuous animals on the docks.
Feather duster worm, Eudistylia vancouveri, easily one of the most conspicuous animals on the docks.
Colonial sea squirts, Botryllus sp. and Botrylloides sp.
Colonial sea squirts, Botryllus sp. and Botrylloides sp.

Colonial sea squirts, those orange-ish blobs in the last picture, are extremely common in marinas. In this photo, each distinct colored blob is an individual colony, and each colony consists of several genetically identical zooids connected by a protective covering called a tunic. Each teardrop-shaped zooid has its own incurrent siphon (the visible hole) through which it sucks in water, and the zooids in a group within a colony share a single excurrent siphon through which waste water is discharged. In Botryllus, the zooids are arranged into flower-like configurations called systems. In Botrylloides the systems are much less distinctive and wind around over the substrate. I’ve outlined a nice colony of Botryllus in the photo below, so you can see the easily recognized systems.

A colony of Botryllus, with zooids arranged in flower-shaped systems.
A colony of Botryllus, with zooids arranged in flower-shaped systems.

Such a wonderful world of animals and algae, right under our feet. Even people who spend a lot of time around boats don’t pay attention to the stuff on the docks. To me it is a secret garden that is easily overlooked but greatly appreciated when you take a moment to get your face down where your feet are.

Motherhood, snail style (Part 2)

Posted on by Allison J. Gong

It has been almost a month since my big female whelk started laying her eggs, and the embryos seem to be developing nicely. The first time I witnessed this phenomenon I saw the egg capsules begin to turn black, and worried that the eggs inside were dead and decomposing. But the cool thing about Kelletia development is that the larvae themselves become darkly pigmented as they develop, which we see as an overall dingy grayness of the egg capsules:

Kellettia eggs

 

Nosy as ever, I pulled one of the egg capsules off the side of the bin and took it back to my desk for closer examination under my dissecting scope. At the “top” of the capsule (the end that is attached to the bin), the material was quite thin, and I could some vague dark lumps inside. They were slowly moving around, so I knew they were alive.

Individual larvae resemble bubbles with dark stuff inside.
Individual larvae resemble bubbles with dark stuff inside.

 

Viability! This makes me happy and encourages me to “liberate” a few larvae to look at under higher magnification. I squeezed out a few veligers and put them under a coverslip with just enough water to keep their shells from cracking but not enough to let them swim away. Here’s a tip for observing small aquatic critters under a microscope:  If you make their universe (i.e., the drop of water you are observing) small, they will be less able to swim away from you. Flattening the drop of water with a judiciously placed coverslip will also help immobilize the creature, as well as taking best advantage of the microscope’s optics.

Early veliger of Kelletia kellettiiNot too much to look at while stationary, is it? You can see a coiled shell (this is a snail after all) and some blobby structures inside it. At this stage the larva isn’t feeding and relies on yolk reserves provided by the mother when she deposited the eggs. Some of the opaque stuff inside the shell is yolk and other bits are various parts of the digestive system. At about 11:00 just underneath the shell there is an elongated transparent area: the larva’s heart; you can see it beating in the video below. The light mohawk-looking structure facing to the right is the larva’s velum, a lobed ciliated structure that the animal will use to swim after it hatches. The last structure of note is the wedge-shaped thing that points to about 5:00; this is the larva’s foot, on the back of which sits the operculum that is used to close up the shell.

After a bit of trial and error I was able to catch some decent video footage through the microscope of a trapped larva:

Kellettia larva under compound scope

The larva rhythmically extends and retracts its velum. Because of the coverslip the larva can’t go anywhere, but if unencumbered it would be able to use that velum to zip around really fast. It is very difficult to keep up with swimming veligers under a microscope!

My guess is that the larvae will begin hatching on their own in the next couple of weeks. They will be washed out of their tub and down the drain of the seawater table, to take their chances in the big ol’ Pacific Ocean.

Motherhood, snail style

Posted on by Allison J. Gong

This week my female Kellet’s whelk (Kelletia kelletii) started laying eggs. She’s been doing this every summer for the past several years. She lives with one other whelk, presumably the father of her brood, as the eggs are both fertilized and viable even though I’ve never seen the snails copulating.

That’s right, copulating. Whelks are predatory marine snails, some of which get quite large. My big female’s shell is a heavily calcified 12 cm or so; she’s a beefy mother! Her mate is smaller, but other than the size difference I wouldn’t be able to tell them apart. Anyway, whelks copulate, with the male using a penis to transfer sperm into the female’s body. Not very different from the way we humans do things, actually.

So at some point in the recent past my whelks copulated, and this week the female began depositing egg cases on the walls of their shared tub. I first noticed them on Monday, but she may have started over the weekend.

Female whelk (right) laying eggs. ©Allison J. Gong
Female whelk (right) laying eggs.
© 2013 Allison J. Gong

Those pumpkin seed-shaped objects are the egg capsules. Each is actually about the size and shape of a pumpkin seed and has a tough outer covering that contains 20-50 developing embryos. After the entire clutch is lain, which usually takes this particular female a week or so, the mom will leave the eggs to develop on their own.

I’ll keep an eye on these eggs for the next week or so, and might be able to get some photos of the embryos and larvae as they begin developing. Keep your fingers crossed!