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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.

My best shot of the comet that has been hanging out near Earth over the past week or so:

Comet NEOWISE
Comet NEOWISE
2020-07-25
© Allison J. Gong

Technical details, for those who care about such things:

  • Nikon D750 with Nikkor 70-200mm f/2.8E FL ED lens, focal length 200mm
  • 10 sec exposure at f/2.8
  • ISO 1000, exposure bias +0.3

Biology is a field of science with very few absolutes. For every rule that we teach, there seems to be at least one exception. I imagine this is very frustrating for students who want to know that Something = Something every single time. It certainly is easier to remember a few rules that apply to everything, than to keep track of all the cases when they don't.

Take, for example, the tube feet of sea stars. Among the generalities that we teach are: (1) sea star tube feet are used for locomotion and feeding; and (2) sea star tube feet are used to stick firmly to rocks and to pry open mussel shells. And we can show many examples of stars clinging to vertical and overhanging surfaces.

Purple sea star sticking to vertical rock surface in the intertidal
Ochre star (Pisaster ochraceus) at Franklin Point
2015-07-15
© Allison J. Gong
Purple sea star sticking to granite boulder in the intertidal
Ochre star (Pisaster ochraceus) at Mitchell's Cove
2019-06-03
© Allison J. Gong

Sometimes we can even find Pisaster doing both at the same time:

Ochre star (Pisaster ochraceus) wrapped around mussel(s) (Mytilus californianus) while clinging to an overhanging surface at Natural Bridges
2020-07-06
© Allison J. Gong

A photo like the one above is merely a snapshot of an event that lasts for hours. What's going on in there? Chances are it's a life-or-lunch battle, with the star trying to pry open the mussel just enough to slide its stomach between the shells while the bivalve is holding its shells clamped shut for dear life.

Each of these behaviors-—sticking to rocks and prying open mussels—is possible because Pisaster ochraceus has suckered tube feet. The tube foot itself has a flattened surface that squishes out a tiny dab of sticky adhesive glue. Together, the tube feet can adhere quite strongly to hard surfaces. I know from experience that it is impossible to pry an ochre star off a rock after it has had a chance to hang on, unless you're willing to damage several dozen tube feet. The tube feet will grow back, but there's no point in causing harm to the animal.

Arm tip of a sea star in a tidepool, showing suckered tube feet sticking to a rock
Tube feet at the arm tip of Pisaster ochraceus
2019-06-18
© Allison J. Gong

So that's the general story we teach in school. For most students, that's the entire story. However, it's always the exceptions, the deviations from the norm, that are the most interesting.

Not every sea star clings to rocks in the intertidal. There are several species that are equally at home on both rocks and sand. And among the rock-clingers, not all are as strong as Pisaster ochraceus. The ochre star's sucker-shaped tube feet are an example of the relationship between form and function: the tube feet's morphology provides the surface area for adhesion that allows the animal to feed and locomote over hard surfaces.

Spiny sand star (Astropecten armatus) at the Seymour Marine Discovery Center
2020-07-15
© Allison J. Gong

As you might expect, sea stars that don't cling to rocks and pry open mussels may not have sucker-shaped tube feet. The spiny sand star, Astropecten armatus, has pointed tube feet! It's hard to see exactly what the tube feet look like in the photo, but here's a video:

See how the tube feet on the underside of that arm end in points rather than suckers? If we revisit the notion of form and function, what questions come to mind when you look at the morphology of the tube feet? And given Astropecten's common name and its habitat, can you think of how it can survive and get around without the sticking power of Pisaster's tube feet?

Observation of Astropecten in its natural habitat would show that it spends a lot of time buried in the sand. It somehow has to get below the surface of the sand, where it feeds on olive snails or other animals that live buried there. How can it do that? Would the generalized sea star sucker-shaped tube feet that we teach to students be useful for burrowing? We can also think about it in a more familiar context: If you had to dig a hole in the ground, would you reach for a plunger? Clearly you wouldn't. You'd use a shovel, or a spade.

Astropecten's pointed tube feet are perfect for punching down between sand grains, enabling the star to work its way down into the sand. The sand star has hundreds of tiny spades at its disposal to use for digging. Circular structures shaped like miniature horse hooves wouldn't be very good at this job, nor would pointed tube feet be very good at sticking to rocks. This animal doesn't obey the "rules" of sea star biology, but form and function, as always, go together.

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.

I'm not the world's most diligent user of iNaturalist, but I do try to upload observations after I've been tidepooling or hiking or poking around outdoors. The other morning I did go to to the intertidal, for only the second low tide series since the COVID quarantine began. State park beaches were closed over the Independence Day holiday weekend, to all except people who could walk there. This rather limited my options, but it was fine because I hadn't been to Natural Bridges in quite a while. It's a site I know well, so I also used the trip to record some video clips to use when I teach Marine Biology in the fall.

My favorite iNat observation for the day is this one:

Bryozoan on a piece of kelp in the shell of a mussel in the mouth of an anemone
2020-07-06
© Allison J. Gong

It's not the prettiest photo, or even the best of the ones I took today. What I like is that it shows four different organisms and demonstrates a few ecological concepts. Let me explain.

The first two organisms are the bryozoan Membranipora membranacea encrusting a small piece of giant kelp Macrocystis pyrifera. This bryozoan really likes to live on giant kelp. In the late summer and fall, it is not uncommon to see kelp thalli so heavily encrusted that blades become brittle and break. The bryozoan also makes the overall kelp thallus both heavier and more brittle than usual, contributing to the annual break up when the winter storms arrive.

The third organism is the mussel, Mytilus californianus, which is probably just an empty shell with the piece of kelp jammed inside.

The fourth organism (or first if you're going from largest to smallest) is the anemone. It is a giant green anemone, Anthopleura xanthogrammica. It's not that uncommon to see them eating mussels, as they are opportunistic predators that will consume anything unfortunate enough to fall onto them. If the mussel shell in indeed empty, then it won't provide the anemone with much in the way of food. However, the bryozoan on the kelp, and even the kelp itself, will. The anemone's gut will be able to digest both of them.

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