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For animals that do essentially nothing when you see them where they live, chitons have a lot of charm. They are the kind of animal that, once you develop the search image for them, you start seeing everywhere. It helps that they are easily recognized as being chitons because of their eight dorsal shell plates—nothing else looks like them. Depending on species, those shell plates can be smooth or sculpted, and pigmented or not. Patterns of sculpting and pigmentation (or lack thereof) are diagnostic features used to distinguish different species. Some species are reliably consistent in appearance and look the same wherever you happen to see them. Other species show a lot of phenotypic variation, often even at a single site.

One of my favorite chitons is Mopalia muscosa, the mossy chiton. It's one of the easiest of our chitons to identify, because its girdle (the layer of tough tissue in which the shell plates are embedded) is densely covered by long, curved spines. They're called spines, but they're quite soft and flexible. Your basic Mopalia muscosa looks like this:

Mossy chiton with bare shell plates, in the rocky intertidal
Mossy chiton (Mopalia muscosa) at Pigeon Point
2016-04-24
© Allison J. Gong

Mopalia muscosa is one of the species whose appearance is quite variable. Many of them wear algae, usually reds but occasionally greens or browns, on their shell plates. Not all species of chiton do this. I've often wondered why some chiton species wear algae and others do not. This individual is probably fairly old, judging by the worn condition of the shell plates. The plates show signs of erosion, but are not decorated. There are some small pieces of coralline algae amongst the spines of the girdle, though, which I always associate with age. Smaller, and presumably younger, M. muscosa tend not to have algae on the girdle even if they are wearing some on the shell plates.

The degree of shell decoration in M. muscosa varies from none, as above, to heavy encrustation. This individual below has been colonized by only a small bit of coralline algae and perhaps some brown diatom-ish film on the edges of the shell plates:

Mossy chiton (Mopalia muscosa) at Pistachio Beach
2021-02-09
© Allison J. Gong

This next one has only a small bit of coralline alga, but sports a jaunty sprig of something quite a bit larger.

Mossy chiton (Mopalia muscosa) at Asilomar
2019-07-04
© Allison J. Gong

This season's fashionable chiton will go all out with the coralline algae, wearing both encrusting and upright branching forms. Look at this:

Mossy chiton (Mopalia muscosa) at Pigeon Point
2017-06-28
© Allison J. Gong

and this:

Mossy chiton (Mopalia muscosa) at Pigeon Point
2018-01-01
© Allison J. Gong

Sometimes the chitons wear the larger leafy red algae, in addition to or in place of the coralline algae. I always think that these individuals must be very old, by chiton standards.

Mossy chiton (Mopalia muscosa) at Pigeon Point
2020-11-14
© Allison J. Gong

And sometimes the chitons are so covered with algae that they blend in perfectly with the surrounding environment.

Mossy chiton (Mopalia muscosa) at Pistachio Beach
2021-04-06
© Allison J. Gong

These chitons can get very heavily fouled by algae. Is there any benefit to the chiton, to carry around a load of red algae? And if wearing algae is for some reason advantageous, is there a way for a chiton to attract algae to settle on their shell plates? Well, let's think about that. Chitons' main predators would be sea stars, crabs, and birds. Sea stars do not locate prey visually, so camouflage would not be very helpful in avoiding them. Birds such as oystercatchers and surfbirds certainly do pry up chitons and limpets, and blending in with the background just might help a chiton go unnoticed by an avian hunter.

Regarding the matter of how the algae end up living on chitons' bodies, I want to start with the question of how prevalent algal fouling is on Mopalia muscosa, and the extent of fouling on the chitons that are wearing algae. A little research study might be a fun way to spend my time in the intertidal. Pigeon Point is a lovely site on a foggy summer morning, and many of the most heavily decorated M. muscosa in my photo library are from there. Yes, I can foresee several visits up the coast over the next few months. Laissez les bons temps rouler!

This morning I went to Pigeon Point to poke around and do some collecting. It's a favorite site of mine, as it's exposed and dynamic, with the diversity you'd expect. Of the sea stars, the most common by far are the six-armed stars in the genus Leptasterias. They are small (less than 8 cm in diameter, often smaller than 1 cm), somewhat drably colored, and sometimes on the underside of rocks, all of which means that they are not always conspicuous. But once you get the right search image, you see them everywhere.

Six arms, see?

Sea stars are well known for their ability to regenerate lost arms. It is not uncommon to see a star that looks healthy in every way except that one of its arms is shorter than the others. This must happen in Leptasterias, too. Searching through my library of pictures of Leptasterias, I did find a couple of examples of regeneration.

When these stars finish regrowing those arms, they will have the typical number of arms for the genus, which is six.

Today I saw something that I'd never seen before. It was a Leptasterias that was regenerating arms. Only this was weird. It had three full-size arms and was growing four!

Sea star with 3 arms and regenerating 4 arms
Leptasterias star regenerating lost arms at Pigeon Point
2021-04-03
© Allison J. Gong

When (if) this star survives, it will eventually have seven arms. And that's strange. I asked my friend Chris Mah, who is the sea star systematist at the Smithsonian, if it was common for Leptasterias to do this. He said he'd never seen it, either. So it is indeed a rare phenomenon.

Now, there are stars in the genus Linckia that actually reproduce by deliberately leaving behind an arm, which then goes on to regenerate the rest of the body. While they do so they look like comets:

"comet" star. One arm is regenerating the remaining arms and central disc.
Linckia multiflora comet in the Maldives
Ahmed Abdul Rahman and Frédéric Ducarme for MDC Seamarc Maldives (CC BY-SA 4.0)

My regenerating Leptasterias isn't quite a comet, but it is doing something equally strange and wonderful. I really wished I could bring it to the lab and keep an eye on it over the next several months. However, Leptasterias are on the no-take list, I think because their populations are so patchy. It is extremely unlikely that I will ever see that same individual again, so we will never know what happens to it. Unless, of course, I happen to come across a 7-armed Leptasterias at Pigeon Point sometime in the future. If you see it, take a photo and let me know!

3

Way back in 2015 I wrote about some Ulva that spawned in a bowl at the lab, and delved into the mysteries of reproduction in the green algae. This morning I was out at Franklin Point and saw this:

Spawning algae at Franklin Point
2021-04-01
© Allison J. Gong

I had seen the sea lettuces (Ulva spp.) spawning in these high pools at Franklin Point before, and usually cursed the murkiness of the water. But today the water was dead calm, with the tide low enough that there were no waves to slosh into the pools. The result was a gorgeous marbled swirl in the water. The patterns were stunning.

Yellow streams of algal spawn in a shallow tidepool
Spawning algae at Franklin Point
2021-04-01
© Allison J. Gong
Yellow streams of algal spawn in a shallow tidepool
Spawning algae at Franklin Point
2021-04-01
© Allison J. Gong
Yellow streams of algal spawn in a shallow tidepool
Spawning algae at Franklin Point
2021-04-01
© Allison J. Gong

What these photos show is the Ulva releasing either spores or gametes. Without microscopic examination it's impossible for me to know whether these tiny cells are spores or gametes. What I can say is that the spawn is released from the distal ends of the thallus, making the body of the alga look ragged.

Sea lettuce in a tidepool. Some blades are clear.
Sea lettuce (Ulva sp.) at the edge of a tidepool at Franklin Point
2021-04-01
© Allison J. Gong

The parts of the thallus that have already spawned are now clear. The tissue itself will soon disintegrate, leaving behind only the healthy green parts, which should be able to regrow.

All of these photos were taken in pools where the spawning itself had either completely or mostly stopped. Obviously when the tide comes back all of this yellow spooge will get mixed up. It's only when the water is perfectly still that these streams would form. It was hard stepping around the pools to take the photos, as the last thing I wanted to do was stomp my big booted foot into a pool and disrupt the beautiful patterns. Fortunately the sun angle was a little cooperative this morning, and I was able to find a pool where active spawning was happening.

What appears to be an act of destruction—the alga's brilliant green thallus being reduced to yellow streaks that drift away with the tide—is really an act of procreation. This is terminal reproduction, literally the last thing an organism does before it dies. Salmon do this, as do annual plants. The sheer amount of algal spawn in these tidepools is astounding. Imagine the number of 2-micron cells needed to color the water to this degree. But if reproducing is the last thing you're going to do in your life, you might as well go all in on your way out, right?

Intact shells are a limited resource in the rocky intertidal. Snails, of course, build and live in their shells for the duration of their lives. A snail's body is attached to its shell, so until it dies it is the sole proprietor of the shell. Once the snail dies, though, its shell goes on the market to whoever manages to claim it. Empty shells tend not to remain on the market for long.

Hermit crabs also live inside snail shells. They are the ones that compete for empty shells when they do become available. Here in California, at least, the hermit crabs can't kill snails for their shells; they have to wait for a snail to die. And once a shell comes on the market, it will have a taker even if it's not the ideal size for the crab. It's not at all uncommon to see hermit crabs that can fit only their abdomen into the shell, leaving the head and legs exposed and vulnerable. On the other end of the spectrum, many hermit crabs are so small that they can pull into the shell and not be seen by an inquisitive tidepool visitor. Anybody taking a snail shell home as a souvenir—where such takes are allowed, of course—must be certain that there is no tiny hermit crab hiding deep in the depths.

Hermit crab in black turban snail shell
Hermit crab (Pagurus samuelis) in shell of turban snail (Tegula funebralis) at Point Piños
2015-05-09
© Allison J. Gong

From a hermit crab's perspective, the best shell is one that is big enough to retreat into but light enough to be carried around. Snail shells come in a variety of shapes and corresponding internal volumes. Turban snails, with their roughly spherical shape, have a large interior space and are coveted by larger hermit crabs. For example, the grainy hand hermit crab (Pagurus granosimanus) seems to really like both black and brown turban snail shells.

Original inhabitant and builder of the shell:

Brown turban snail partially withdrawn into shell
Brown turban snail (Tegula brunnea) at Pistachio Beach
2021-02-09
© Allison J. Gong

And opportunistic second inhabitant of the same type of shell:

Grainy hand hermit crab in turban snail shell
Grainy hand hermit crab (Pagurus granosimanus) in brown turban snail (Tegula funebralis) shell
2018-06-01
© Allison J. Gong

Other snails are not even remotely spherical. Olivella biplicata, for example, is shaped like the pit of an olive. Unlike Tegula, of which both intertidal species are found in rocky areas, O. biplicata burrows in sand. Note the shape and habitat of this olive snail:

Olive snail
Olive snail (Olivella biplicata) burrowing through sand at Whaler's Cove
2019-11-24
© Allison J. Gong

These olive snails have a smaller internal volume, and thus tend to house smaller hermit crabs. Young individuals of P. granosimanus can be found in olive snail shells, but they quickly outgrow the cramped quarters and need to find a larger home. Smaller hermits such as Pagurus hirsutiusculus, though, are often found in olive shells.

Any hermit crab that finds itself robbed of its snail shell has a short life expectancy. The front end of the hermit resembles the front end of any crab, with the familiar armored legs, claws, eyestalks, and antennae. But the abdomen is soft and unarmored, covered by only a thin cuticle. The abdomen is coiled to follow the coiling of the snail shell, which allows the crab's body to curl around the columella, the central axis around which the shell spirals. In this way the crab can hang onto its snail shell and resist a tug by a would-be predator. A strong enough tug, though, will rip the crab's front end (head + thorax) away from its abdomen. So if you ever find yourself with a hermit crab in hand, do not be tempted to remove it from its shell by yanking it out!

The next time you encounter gastropod shells in the tidepools and want to know whether the inhabitant is a snail or a hermit crab, watch to see how it moves. Hermit crabs scuttle, as crabs do, while snails glide along very slowly. You would also notice a difference as you pick up the shell: snails stick to the rock with their foot, which you will feel as a suction. Hermit crabs don't stick at all, so if the shell comes away easily it likely houses a crab instead of a snail. See? Easy peasy lemon squeezy!

Sometimes even a well-known site can present a surprise. Here's an example. Yesterday I went up to Davenport to scope things out and see how the algae were doing. This is the time of year that they start growing back after the winter senescence. I also took my nature journal along, hoping to find a spot to sit and draw for a while.

The first thing I noticed was the amount of sand on the beach. Strong winter storms usually carve sand off the beaches, making them steeper. And during the calmer months of summer the beaches are flatter and less steep. Yesterday the beach was very thick and flat. It makes trudging across the sand in hip boots much easier!

The accumulation of sand meant that I could walk around the first point. Unless the tide is extremely low, such as we see around the solstices, the water is too deep for that. But yesterday I walked around it, and it wasn't until I got to the other side that it occurred to me that: (1) hey, I walked around the point; and (2) I could do that only because there was so much sand. See, a thick beach with a lot of sand makes a mediocre low tide feel lower because the water isn't as deep as it would be if the beach were thinner. When the tide isn't low enough for me to walk around the point, I have to clamber down a cliff. The cliff height varies depending on how much sand has built up, obviously, but is about head height for me. Getting down usually involves scooting on my butt and hoping my feet land on something that isn't slippery. As with most climbing, up is easier and less scary than down.

It's hard to imagine the amount of sand there was yesterday. Look at this picture.

Flat rock area and sandy area
North of Davenport Landing Beach
2021-02-08
© Allison J. Gong

See how the rocks in the foreground end? Usually that's the edge of the cliff. Yesterday I could have just taken a tiny step off the top of the cliff onto sand. That's over 1.5 meters of sand in that one spot! If the couple in the background were visiting this area for the first time, they'd have no idea of the conditions that made it so easy for them to get out onto the reef.

There was a lot of sand in the channels between rocks, too.

Sand between rocks in the intertidal
Intertidal area north of Davenport Landing Beach
2021-02-08
© Allison J. Gong

Normally those channels are deeper. You can see that some anemones were able to reach to the surface of the sand, but many more are buried, along with any other critters and algae unfortunate enough to be attached to the lower vertical surfaces. And while some of them will either suffocate or be scoured off as the sand washes away, many will survive and be ready to get on with life.

The second surprise of the day was a bright orange object. What I could see of it was about as big as my thumb, and at first I thought it was a nudibranch. Then when I crept closer for a better look, what popped into my head was "snailfish". Which was an odd thing, because I'd never seen a snailfish before. But something about the creature's posture looked somehow familiar.

Orange fish with large head and tail wrapped around the body
Tidepool snailfish (Liparis florae) at Davenport Landing
2021-02-08
© Allison J. Gong

Fortunately I had the presence of mind to take photos before trying to draw this little fish, because this is all I had time to get:

When I spooked the critter it took off really fast, confirming that it was no nudibranch. It was, indeed, a snailfish! It came to rest in a small hole in a rock, from where it looked out at me.

Tidepool snailfish (Liparis florae) at Davenport Landing
2021-02-08
© Allison J. Gong

The snailfishes are a very poorly studied group. As a group they are related to the sculpins. There are snailfishes throughout the northern temperate and polar regions, from the intertidal to the deep sea. iNaturalist shows 43 observations of L. florae, eight of which are in California. Before yesterday, none had been recorded at Davenport Landing.

Map of northeast Pacific coast, showing sighting of tidepool snailfish recoreded in iNaturalist
Observations of tidepool snailfish (Liparis florae) recorded in iNaturalist
2021-02-09
© iNaturalist

So there you have it, a snailfish! We don't know much about any of the snailfish species, even the intertidal ones. They apparently have pelvic fins modified to from a sucker, similar to the clingfishes, but I didn't have a chance to examine this specimen closely enough to confirm that. I don't know why they are called snailfishes, either. They're not snail-shaped at all.

Now, about that thing up there where I said "snailfish" came to mind even though I'd never seen one before. That happens quite a bit—a name will jump into my head before I've had a chance to think about it. Sometimes I'm wrong, but often I'm right. I know I hadn't seen a live snailfish before, but obviously I'd seen photos of them or I wouldn't have been able to recognize this orange creature as being one. It's fascinating how the brain forms search images, isn't it?

According to my notes at the lab, the last time I spawned urchins was December of 2016, making it four years ago. It has always been something I enjoyed doing, but I didn't have a reason to until now.

When the coronavirus pandemic began almost a year ago now, access to all facilities at the marine lab was restricted to a group of people deemed essential. In my case, "essential" had to do with the fact that I keep animals alive. There were many hoops to jump through and inane questions to answer—for example, "What will happen if you don't go in to check on water and food?" and "How many animals will die if you do not have access to the lab, and how much effort [i.e., $$$] would it take to replace them?"—but in the end someone higher up in the food chain exercised some common sense and decided to let me have continuous access to the lab. So I've been at the lab pretty much every day, to check on things and make sure that air and water are flowing.

So over the summer we were running sort of bare-bones operations at the lab. There were many fewer people looking after everyday things. The autoclave broke and wasn't fixed until September. One of the casualties of this less-than-normal vigilance was one of the cultures in the phytoplankton lab. Our Rhodomonas flasks had been contaminated since late 2019, and we were struggling to rescue them. I tried so hard to keep them going ahead of the contamination, but ultimately failed. As of this writing all of the old Rhodomonas cultures have died.

In October, after the autoclave had been repaired, I decided to take action and replace our inevitably doomed Rhodomonas cultures. I found a company that sells small aliquots of many marine microalgae and ordered a strain of Rhodomonas that was isolated in Pacific Grove. May as well see if a local strain of algae works as a food for local larvae, right? The new Rhodomonas cultures seem to be growing well and it's time to see of urchin larvae will eat and thrive on it.

Equipment and glassware used to spawn sea urchins

About a month ago I collected 10 urchins to spawn. Yesterday was their lucky day! Purple sea urchins (Strongylocentrotus purpuratus) are broadcast spawners, and spawning is both inducible and synchronous. We can take advantage of the inducibility to make them spawn when we want, as long as they have ripe gonads. The difficulty is that we can't tell by looking whether or not an urchin is gravid, so all we can do is try to induce them and then hope for the best.

As I've written before, we induce spawning in sea urchins by injecting them with a solution of potassium chloride (KCl). KCl is a salt solution that causes an urchin's gonopores to open and release gametes if the gonads are ripe. I shot up 10 urchins yesterday, and eight of them spawned. An 80% spawning rate isn't bad, but only two of the eight were female and neither of them had a lot of eggs to give.

Since the gonopores are located on the aboral (top) of the urchin, the easiest way to collect eggs is to invert the animal on a beaker of seawater, like so:

Female sea urchin (Strongylocentrotus purpuratus) spawning
2021-01-12
© Allison J. Gong

In nature the eggs, which are a pale orange color, would be whisked away by currents to be (hopefully) fertilized in the water column. In the lab we can collect the eggs in the beaker, as follows:

This is much less damaging to the animal than trying to pipet eggs off the top of the urchin.

We try to collect sperm and keep it dry, so there is no putting males upside-down on beakers of water. Instead we pipet up the sperm and keep it dry in dishes on ice. When it's time to fertilize the eggs we dilute the sperm with filtered seawater and add a small amount to the eggs.

One of my favorite things ever is watching fertilization take place in real time, under the microscope. It truly is one of nature's most amazing phenomena. It is a great thrill to watch the creation of new beings.

In the video you see eggs being bombarded with sperm, probably at much higher concentrations than they would encounter in the wild. It is common knowledge that it takes only one sperm to fertilize an egg, but what would happen if two sperm penetrated an egg at the same time? I've written about polyspermy and the fast and slow blocks thereto, in case you'd like to refresh your memory about what is happening in the video.

A successfully fertilized egg is easily recognized by its fertilization envelope, which is the slow block to polyspermy.

Zygotes of the purple sea urchin (Strongylocentrotus purpuratus)
2021-01-12
© Allison J. Gong

After fertilization, the next step to watch for is the first cleavage division, which occurs about two hours later.

2-cell embryos of the purple sea urchin (Strongylocentrotus purpuratus)
2021-01-12
© Allison J. Gong

Aren't they pretty?

Over the next day or so the cleavage divisions continue, resulting in the stage that hatches out of the fertilization envelope. This stage is a blastula, which is a hollow ball of ciliated cells. The hollow space inside is called the blastocoel, and it is here that the larval gut will soon develop.

Blastula of the purple sea urchin (Strongylocentrotus purpuratus)
2021-01-12
© Allison J. Gong

It's easier to see the 3-dimensional structure of the blastula by watching it spin around.

As the blastula rotates under the coverslip, you can see the ciliary currents that would propel it through the water. You also see some objects that look like sperm and are, in fact, dead sperm, getting caught up in the currents.

The blastula is the same size as the egg. The embryo can't begin to grow until it eats, which won't happen until it has a gut. Over the next few days an invagination will begin at a certain location on the blastula which is called the blastopore; this invagination will eventually form the first larval gut. At that point I will have to start feeding them and calling them larvae.

And just to remind you of our humble beginnings, we begin life in much the same way as sea urchins. That blastopore, or initial opening to the larval gut, is the anus. The mouth doesn't exist until the invagination breaks through to the opposite end of the embryo. So yes, like the sea urchin, you had an anus before you had a mouth!

4

On the penultimate day of 2020 I met up with my goddaughter, Katherine, and her family up at Pigeon Point to have two adventures. The first one was to find a marble that had been hidden a part of a game. We got skunked on that one, although the marble was found after we left and the hider had sent an additional clue. The second adventure was an excursion to the tidepools. I've had a lackadaisical attitude towards the afternoon low tides this winter, not feeling enthusiastic about heading out with all of the people and the wind and having to fight darkness. But the invitation to join the marble hunt, on a day with a decent low tide, meant that I could spend a good deal of quality time with Katherine.

It is not unusual for a promising low tide to be cancelled out by a big swell. It happens, especially during winter's combination of afternoon lows and occasional storms. The swell yesterday was pretty big.

Here's the view to the north, from Pigeon Point:

Looking north from Pigeon Point
View to the north from Pigeon Point
2020-12-30
©Allison J. Gong

All that whitewash breaking over the rocks is not good for tidepooling, especially with small kids in tow.

This is how things looked to the south of the point:

View to the south from Pigeon Point
2020-12-30
©Allison J. Gong

This is Whaler's Cove, a sandy beach that lies on the leeward side of the point itself. See how the water is much calmer? It's amazing how different the two sides of the point are, in terms of hydrography, wind, and biota. The south side is much easier to get to, especially for newbies or people who are less steady on their feet. Being sheltered from the brunt of the prevailing southbound current means that the biological diversity is, shall we say, a bit subdued when compared to what we see on the north side of the point.

I first took Katherine tidepooling when her sister, Lizzie, was an infant riding in her mom's backpack. Katherine was about four at the time. Her mom and I were suprised at how much she remembered. She recognized the anemones right away, even the closed up cloning anemones (Anthopleura elegantissima) on the high rocks. She remembered to avoid stepping on them—that's my girl!

She wasn't all that keen on touching the anemones, though, even after we told her it feels like touching tape.

Giant green anemone in tidepool
Giant green anemone (Anthopleura xanthogrammica)
2020-12-30
©Allison J. Gong

She did like the sea stars, too. Purple is my favorite color and I think hers, too, so the purple and orange ochre stars were a hit. It was nice to see two large healthy ones.

I had some actual collecting to do, so it was a work trip for me. Late December is not the best time to collect algae, but I wanted to bring some edible seaweeds back to the lab to feed animals. We haven't had any kelp brought in since the late summer, and urchins are very hungry. They will eat intertidal seaweeds, though, and when I go out to the tidepools I bring back what I can. It will be a couple of months until we see the algae growing towards their summer lushness, but even a few handfuls of sea lettuce will be welcome to hungry mouths.

Bright green sea lettuce growing with red algae
Sea lettuce (Ulva sp.)
2020-12-30
©Allison J. Gong

Katherine and I walked up the beach for a little way to study one of the several large-ish crab corpses on the sand. This one was a molt rather than an actual corpse.

Rock crab molt on sand
Rock crab (Romaleon antennarium) molt
2020-12-30
©Allison J. Gong

Katherine found the missing leg a little way off, and we discussed why we call these limbs legs instead of arms. "They use their claws to pinch things, like hands," she said. Not wanting to get into a discussion of serial homology and crustacean evolution with a 6-year-old, I told her that calling the claws "hands" isn't a bad idea, since they are used a lot like the way we use our hands. But, I continued, the crab walks on its other limbs like we walk with our legs, so can we call those legs? She was happy to agree with that. I can tell I will have to be careful about how I explain things to her, so that she doesn't come up with some wonky ideas about how evolution works.

In the meantime, Lizzie, the little sister, was having a grand old time. She flooded her little boots without a complaint and, after her mom emptied the water from them, squelched happily along with soggy socks. That girl may very well grow up to be a marine biologist!

Once the sun went behind the cliff it started getting cold. With one child already wet we decided to head back. On our way up the beach we saw this thing, which I pointed out to Katherine:

"What is it?" she asked. When I asked what she thought it was she cocked her head to one said and said, "It looks like a rock." Then I told her to touch it, which she didn't want to do. So I picked it up and turned it over, to show her the underside:

Gumboot chiton (Cryptochiton stelleri)
2020-12-30
©Allison J. Gong

These big gumboot chitons do look more interesting from this side, because you can at least see that they are probably some kind of animal. Katherine had seen some smaller chitons on the rocks, so she had some idea of what a chiton is, but these are so big that they don't look anything like the ones we showed her earlier. Plus, with their shell plates being covered with a tough piece of skin and invisible, there are no outward signs that this bizarre thing is indeed a chiton. Katherine was not impressed.

At this time of year, when the sun decides to go down it goes down fast. But as we were walking back across the rocks the tide was at its lowest, so there was more terrain to explore. Then it was back up the stairs to the cars, where we could get warm and dry.

Beach and lighthouse at Pigeon Point

Oh, and Katherine and her mom and sister were able to find the hidden marble! They also hid one of their own for someone else to find.

At the end of August I got to play animal wrangler for a film production. Back in the late winter I had been contacted by an intern at KQED in San Francisco, who wanted to shoot some time-lapse footage of anemones dividing. We went out and collected anemones, I got them set up in tanks at the marine lab, and then COVID19 hit and everything went on shut-down. The intern finished her internship remotely and went on to her next position, and in the meantime the anemones stubbornly refused to divide.

The KQED lead videographer for the Deep Look video series, Josh Cassidy, who would had recorded the anemones dividing if they had divided and if the marine lab were not closed, asked me over the summer if we could somehow arrange to meet up to film something else. He had heard of some research that showed the emergent property of sea stars bouncing as they walk along on their many tube feet. Is there any way, he asked, that he could film some of the stars at the lab?

Well, filming at the lab was out of the question. Only essential personnel are allowed in the buildings, and there was no way I could sneak in Josh and all of his gear. We discussed options such as meeting up at a beach but I decided that I needed more control of the site to keep things safe for the animals. We ended up borrowing some friends' back yard for the day, which worked out pretty well. They have a covered pavilion, which was ideal because of course it turned out to be hot the day we filmed. I had several bags of frozen seawater to keep things cool-ish, two coolers for the movie stars themselves, a battery-operated air pump, and 30 gallons of seawater on hand.

Filming for production purposes takes a really long time. Even for a short film, we were working most of the day. Because of course most of the stars were uncooperative. They don't have anything even remotely resembling a brain, but damn if they can't bugger things up. I was feeling kind of bad that my animals were being such troublemakers; Josh, fortunately, was much more patient with them.

And here's the film! You'll see my right hand for about 1.5 seconds.

I didn't realize this at the time, but Josh also writes an article for each episode of Deep Look, for the KQED website. For this episode the article describes the research into the biomechanics of sea star bouncing. I'm quoted at the end.

So watch this short film. I hope it helps put a little bounce in your step.

Every summer, like clockwork, my big female whelk lays eggs. She is one of a pair of Kellett's whelks (Kellettia kellettii) that I inherited from a labmate many years ago now. True whelks of the family Buccinidae are predatory or scavenging snails, and can get pretty big. The female, the larger of the two I have, is almost the length of my hand; her mate is a little bit smaller.

Many marine snails (e.g., abalones, limpets, and turban snails) are broadcast spawners, spewing large numbers of gametes into the ocean and hoping for the best. These spawners have high fecundity, but very few, if any, of the thousands of eggs shed will survive to adulthood. We say that in these species, parental investment in offspring extends only as far as gamete production. Fertilization and larval development occur in the water column, and embryos and larvae are left to fend for themselves.

The whelks, on the other hand, are more involved parents. They maximize the probability of fertilization by copulating, and the female produces yolky eggs that provide energy for the developing embryos and larvae. Rather than throw her eggs to the outside world and hoping for the best, the female whelk deposits dozens of egg capsules, each of which contains a few hundred fertilized eggs.

Over a period of about three weeks I shot several time-lapse video clips of the mama whelk laying eggs. Due to the pandemic we need to work in shifts at the lab. Fortunately I have the morning shift, which means I can start as early as I want as long as I leave before 11:00 when the next person comes in. Each 2.5-hr stint at the lab yielded about 30 seconds of video, not all of which was interesting; even in time-lapse, whelks operate at a snail's pace. Still, I was surprised at how active the female could be while she was apparently doing nothing.

The freshly deposited capsules are a creamy white color, as are the embryos inside them. As the embryos and then larvae grow, they get darker. Each of the fertilized eggs develops through the first molluscan larval stage, called a trochophore larva, within its own egg membrane. The embryo, and then the trochophore, survives on energy reserves provided by the mother snail when she produced the egg. These larvae don't hatch from their egg membrane until they've reached the veliger stage.

Pumpkin seed-shaped egg capsule of the whelk Kellettia kellettii, 13 mm tall.
Egg capsule of Kellettia kellettii
2020-06-20
© Allison J. Gong
Veliger larva of Kellettia kellettii
2020-07-25
© Allison J. Gong

The veliger larva gets its name from a lobed ciliated structure called a velum. Gastropods and bivalves have veliger larvae. As you might expect, the bivalve veliger has two shells, and the gastropod veliger has a coiled snail shell. These Kellettia veligers have dark opaque patches on the foot and some of the internal organs. That coloration is what you see in the photo of the egg capsule. You can see below which of the egg capsules are the oldest, right?

Mated pair of Kellettia kellettii and their egg capsules
2020-07-25
© Allison J. Gong

By the time the veligers emerge from the egg capsule, they have burned through almost all of the energy packaged in the yolk of the egg. They need to begin feeding very soon. The current generated by the beating cilia on the velum both propels the larva through the water and brings food particles to the larva's mouth. The velum can be pulled into the shell, and, as in any snail the opening to the shell can be shut by a little operculum on the veliger's foot. As is the case with most bodies, the veliger is slightly negatively buoyant, so as soon as it withdraws into the shell it begins to sink. However, once the velum pops back out the larva can swim rapidly.

Watch how the veliger swims. You can also see the heart beat!

So now the egg capsules are being emptied as the larvae emerge. I'm not keeping the veligers, so they are making their way through the drainage system back out to the ocean. As of now there are no iNaturalist observations of Kellettia kellettii in the northern half of Monterey Bay, so it appears that for whatever reason the whelks have not been able to establish viable populations here. Or it might be that the whelks are here but there aren't enough SCUBA divers in the water to see them.

These little veligers will be very lucky if any of them happen to encounter a subtidal habitat where they can take up residence as juvenile whelks. Even for animals that show a relatively high degree of parental care, the chances of any individual larva surviving to adulthood are exceedingly small. However, for the reproductive strategy of Kellettia to have evolved and persisted, there must be a payoff. In this case, the reward is an equal or greater reproductive success compared to snails that simply broadcast thousands of unprotected eggs into the water. Some gastropods such as the slipper shell Crepidula adunca, take parental care even further than Kellettia; in this species the mother broods her young under her shell until they've become tiny miniatures of herself, then she pushes them out to face the world and find a turban snail to live on. Crepidula adunca does not have a swimming larval stage at all. The fact that we see a variety of strategies—many eggs with little care, fewer eggs with more care, and brooding—indicates that there's more than one way to be successful.

I've written before about the rocky intertidal as a habitat where livable space is in short supply. Even areas of apparently bare rock prove to be, upon closer inspection, "owned" by some inhabitant or inhabitants. That cleared area in the mussel bed? Look closely, and you'll likely find an owl limpet lurking on the edge of her farm.

See?

Owl limpet at edge of her territory, a clear area surrounded by mussels.
Owl limpet (Lottia gigantea) on her farm at Natural Bridges
2017-04-01
© Allison J. Gong

And of course algae are often the dominant inhabitants in the intertidal.

Assemblage of algae in the intertidal
Assemblage of algae north of Waddell Creek
2020-06-09
© Allison J. Gong

When bare rock isn't available, intertidal creatures need other surfaces to live on. To many small organisms, another living thing may be the ideal surface on which to make a home. For example, the beautiful red alga Microcladia coulteri is an epiphyte that grows only on other algae. Smithora naiadum is another epiphytic red alga that grows on surfgrass leaves.

We describe algae that grow on other algae (or plants) as being epiphytic (Gk: epi "on" + phyte "plant"). Using the same logic, epizooic algae are those that live on animals. In the intertidal we see both epiphytic and epizooic algae. For many of them, the epizooic lifestyle is one of opportunism--the algae may not care which animal they live on, or even whether they live on an animal or a rock. Some of the epiphytes, such as Microcladia coulteri, grow on several species of algae; I've seen it on a variety of other reds as well as on a brown or two (feather boa kelp, Egregia menziesii, immediately comes to mind). Smithora naiadum, on the other hand, seems to live almost exclusively on the surfgrass Phyllospadix torreyi.

Animals can also live as epiphytes. The bryozoan that I mentioned last time is an epiphyte on giant kelp. Bryozoans, of course, cannot move once established. Other animals, such as snails, can be quite mobile. But even so, some of them are restricted to certain host organisms.

The aptly called kelp limpet (Discurria insessa), lives only on the stipe of E. menziesii, the feather boa kelp. Its shell is the exact same color as the kelp where it spends its entire post-larval life. Larvae looking for a place to take up a benthic lifestyle settle preferentially on Egregia where adult limpets already live. It's a classic case of "If my parents grew up there it's probably a good place for me."

Limpet on stipe of feather boa kelp
Discurria insessa on stipe of Egregia menziesii
2020-06-07
© Allison J. Gong

The limpets cruise up and down the stipe, grazing on both the epiphytic diatoms and the kelp itself. They can make deep scars in the stipe and even cause breakage. Which makes me wonder: What happens to the limpet if it ends up on the wrong end of the break? Does it die as the broken piece of kelp gets washed away? Can it release its hold and find another bit of Egregia to live on? Somehow I doubt it.

Discurria insessa on stipe of Egregia menziesii
2018-05-16
© Allison J. Gong

The last time I was in the intertidal I encountered another epiphytic limpet. Like the red alga Smithora naiadum, this snail one lives on the narrow leaves of surfgrass. It's a tiny thing, about 6 mm long, and totally easy to overlook, given all the other stuff going on in the tidepools. But here it is, Tectura paleacea. Its common name is the surfgrass limpet, which actually makes sense.

Top view of surfgrass limpet on leaf of surfgrass
Surfgrass limpet (Tectura paleacea) on surfgrass (Phyllospadix torreyi) at Davenport Landing
2020-07-07
© Allison J. Gong

Tectura palacea feeds on the microalgae that grow on the leaves of the surfgrass, and on the outer tissue layer of the plant. They can obviously grow no larger than their home, so they are narrow, about 3 mm wide. But they are kind of tall, although not as tall as D. insessa.

Lateral view of surfgrass limpet on leaf of surfgrass
Surfgrass limpet (Tectura paleacea) on surfgrass (Phyllospadix torreyi) at Davenport Landing
2020-07-07
© Allison J. Gong

Cute little thing, isn't it? Tectura palacea seems to have avoided being the focus of study, as there isn't much known about it. Ricketts, Calvin, and Hedgpeth write in Between Pacific Tides:

A variety of surfgrass (Phyllospadix) grows in this habitat on the protected outer coast; on its delicate stalks occurs a limpet, ill adapted as limpets would seem to be to such an attachment site. Even in the face of considerable surf, [Tectura] palacea, . . . , clings to its blade of surfgrass. Perhaps the feat is not as difficult as might be supposed, since the flexible grass streams out in the water, offering a minimum of resistance. . . The surfgrass provides not only a home but also food for this limpet, which feeds on the microalgae coating the blades and on the epithelial layers of the host plant. Indeed, some of the plant's unique chemicals find their way into the limpet's shell, where they may possibly serve to camouflage the limpet against predators such as the seastar Leptasterias hexactis, which frequents surfgrass beds and hunts by means of chemical senses.

And that seems to sum up what is known about Tectura palacea. There has been some work on its genetic population structure, but very little about the limpet's natural history. The intertidal is full of organisms like this, which are noticed and generally known about, but not well studied. Perhaps this is where naturalists can contribute valuable information. I would be interested in knowing how closely the populations of T. palacea and Phyllospadix are linked. Does the limpet occur throughout the surfgrass's range? Does the limpet live on both species of surfgrass on our coast? In the meantime, I've now got something else to keep my eye on when I get stranded on a surfgrass bed.

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