Skip to content

5

Published on 5 Comments on In Memoriam

On the afternoon of July 31, 2020 the world of invertebrate biology and marine ecology in California lost a giant in our field. Professor Emeritus John S. Pearse died after battling cancer and the aftereffects of a stroke.

John Pearse in the intertidal at Soquel Point
2017-05-28
© Allison J. Gong

John was one of the very first people I met when I came to UC Santa Cruz. Before we moved here, my husband and I came and met with John, who was not my official faculty sponsor but agreed to show us around so we could check out different areas for a place to live. In fact, I had applied to the department to do my graduate work in John's lab, but because he was considering retirement the department wouldn't let him take on a new Ph.D. student. But when we needed some help getting acquainted with Santa Cruz, John and his wife, Vicki Buchsbaum Pearse, graciously let us stay at their house and spent a day driving us around town and showing us eateries as well as potential neighborhoods.

By happenstance we ended up living down the hill from John and Vicki. We had met their blue duck, Lily, and I used to fill spaghetti sauce jars with snails from our tiny yard and trudge up the hill to feed them to her. She gobbled them up like they were her favorite treat.

As one of the regional experts in invertebrate biology, John was on all of my graduate committees. There were always a half-dozen or so of us grad students working with invertebrates, and we all tended to hang out together. John was one of the things we shared in common. And even if he wasn't technically on one's committee, he would always be available for consultation or advice as needed.

When John retired, he didn't leave the campus. He remained a presence at the marine lab, and still did field work. He started incorporating young students in his long-term intertidal monitoring research, which morphed into the LiMPETS project. The combination of working with students while producing robust scientific data was the perfect distillation of John's legacy. He said this about LiMPETS:

This is one of the best things I could ever do to enhance science education and conservation of our spectacular coastline. Working with teachers and their students is a wonderful and fulfilling experience.

John S. Pearse, Professor Emeritus
UC Santa Cruz

The last time I saw John was in the summer of 2019, during his annual Critter Count. He started these Critter Counts back in the 1970s, monitoring biota at two intertidal sites in Santa Cruz. These sites have since been incorporated into the LiMPETS program. I'm sure it made John smile whenever he thought of generation after generation of schoolkids traipsing down to the intertidal with their quadrats and transect lines, counting organisms the way he had for so many years.

When I started teaching my Ecology class, John suggested that I take the students out to Davenport Landing to monitor at the LiMPETS site there. That is another of his long-term sites, and he was worried about losing information if it were not sampled at least once a year. My students have done LiMPETS monitoring three years now, and John accompanied us on at least two of those visits. I tried to impress upon the students that having John Pearse himself come out with us was a Big Deal, but am not sure I was able to convince them of how fortunate they were. I bet there are a lot of marine biologists in California who would dearly love to go tidepooling with John. And now no one else will.

John Pearse and Todd Newberry, the other professor who gets the blame for how I think about biology, taught an Intertidal Biology class. I came along on many of the field trips the last year they taught it. I remember getting up before dawn to drive down to Carmel, park in the posh neighborhood streets, and walk down to meet John and Todd in the intertidal. I remember slogging through the sticky mud at Elkhorn Slough, digging for Urechis and hearing John shout "It's a goddamned brachiopod!" from across the flat. I remember bringing phoronid worms back to the lab, looking at them under the scope, and watching blood flow into and out of their tentacles. I remember John taking an undergraduate, Jen, and me out to Franklin Point, and showing me my very first staurozoans. That was probably around 1996, and I'm still in love with those animals.

I'm no John Pearse or Todd Newberry, but I'm a small part of their giant legacy in this part of the world. I strive to instill in my students the joy and intellectual pleasure in studying the natural world that I inherited from John and Todd. Partly to honor them, but mostly because it suits my own inclinations, I'm on a one-woman crusade to bring natural history back into modern science and science education.

I've spent the last two mornings in the intertidal at two of the LiMPETS sites, as part of a personal tribute to John. I thought there would be no greater way to memorialize John than by spending some quality time in the intertidal, where he trained so many young minds. I was thinking of him as I took photos, and thought he would be pleased if I shared them.

Natural Bridges—4 August 2020

Shore crab (Pachygrapsus crassipes)
2020-08-04
© Allison J. Gong
  • Owl limpet (Lottia gigantea)
    2020-08-04
    © Allison J. Gong
  • Purple urchins (Strongylocentrotus purpuratus)
    2020-04-08
    © Allison J. Gong

And because, like me, John had a special affinity for the anemones:

Sunburst anemone (Anthopleura sola)
2020-08-04
© Allison J. Gong
Sunburst anemone (Anthopleura sola)
2020-08-04
© Allison J. Gong

And he would have loved this. What is going on here? How did this pattern come to be?

Anemones (Anthopleura elegantissima and possibly A. sola)
2020-08-04
© Allison J. Gong

And look at this, three species of Anthopleura in one tidepool! Can you identify them?

Tidepool at Natural Bridges
2020-08-04
© Allison J. Gong

Davenport Landing—5 August 2020

It was windy and drizzly this morning. I ran into a friend, Rani, and her family out on the flats; they were leaving as I arrived. I hadn't seen her since before the COVID-19 lockdown began back in March. She was also visiting the tidepools to honor John Pearse. We chatted from a distance and exchanged virtual hugs before heading our separate ways.

It felt like a John Pearse kind of morning. I recorded the video clip I needed for class, collected some algae and mussels for a video shoot tomorrow, and took a few photos.

A typical intertidal assemblage (sea stars, sea anemones, and algae) at Daveport Landing
2020-08-05
© Allison J. Gong

And even though I'm not very good at finding nudibranchs, even I couldn't miss this one. It was almost 4 cm long!

Nudibranch (Triopha maculata) at Davenport Landing
2020-08-05
© Allison J. Gong

The ultimate prize for any tidepool explorer is always an octopus. When I take newbies into the field that's what they always want to see. I have to explain that while octopuses are undoubtedly there and common, they are very difficult to find. You can't be looking for them, unless you really like being frustrated.

But John must have been with me in spirit this morning, because I found this:

Red octopus (Octopus rubescens) at Davenport Landing
2020-08-05
© Allison J. Gong

It was just a small one, with the mantle about as long as my thumb. I found it because I spotted something strange poking out from a piece of algae. It was the arm curled with the suckers facing outward. I touched it, and the arm retracted. It didn't seem to like how I tasted.

And lastly, for me this is the epitome of John Pearse's legacy: Working in the intertidal, showing students how to identify owl limpets. I hope they never forget what it was like to learn from the man who with his wife, literally wrote the book about invertebrates and founded LiMPETS.

John Pearse in the intertidal with my students
2016-04-29
© Allison J. Gong

RIP, John S. Pearse. You left behind some enormous shoes to fill and a legacy that will stretch down through generations. I count myself lucky to have spent time with you in the field and in the lab. While I will miss you sorely, it is my privilege to pass on your lessons. Thank you for all you have taught me.

Published on Leave a comment on Emergence

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.

  • Female whelk (Kellettia kellettii)
  • Male whelk (Kellettia kellettii)

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.

Published on Leave a comment on NEOWISE

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

Published on Leave a comment on An exception to the rule

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.

Published on Leave a comment on Plants and algae as real estate

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.

L: Microcladia coulteri on Mazzaella. R: Smithora naiadum on surfgrass
Davenport Landing
2020-07-07

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.

Published on Leave a comment on Four for the price of one

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.

2

Published on 2 Comments on Feeding babies

For some reason, the barn swallows at the marine lab like building their nests above doors. It seems that little 1/2-inch ledge of the door frame provides support for the mud nest. And the birds don't always choose little-used doors, either. This year a pair constructed their nest above one side of a double-door that people walk through all day. The mother laid and incubated her eggs, but would occasionally get flushed off the nest if someone came through the door. I always tried not to disturb her any more than necessary. The animal is always right, so I figured she knew what she was doing.

The eggs hatched about a week ago, I think. The mom would sometimes leave the nest when people approached, and even though I couldn't see anything in the nest I'd hear little cheeps. Earlier this week I thought I could see little heads poking above the edge of the nest.

It seems there are three baby birds in this nest!

Trio of baby barn swallows in nest
Trio of nestling barn swallows (Hirundo rustica)
2020-06-27
© Allison J. Gong

I haven't spent much time watching the nest closely, because I don't want to scare the mother off and keep her away. Today I was lucky and stuck around just long enough, and with the big camera at hand, to capture both parents returning to feed the babies. The first parent arrived with an insect and landed on the nest. The other parent alit on the door frame.

Parent barn swallows return to the nest
Parents arrive at the nest
2020-06-27
© Allison J. Gong
Parent with insect, and babies waking up
2020-06-27
© Allison J. Gong
Baby barn swallow opening mouth to be fed
Open wide!
2020-06-27
© Allison J. Gong
Parent barn swallow feeding a nestling
So many gaping mouths to feed!
2020-06-27
© Allison J. Gong

After depositing the insect into one of the gaping yellow mouths, the first parent flies off. The second parent doesn't seem to have anything to offer the babies, though.

Three nestling barn swallows and one parent
Not enough bugs to go around
2020-06-27
© Allison J. Gong

Ooh, maybe this parent has food!

Three nestling barn swallows, and second parent flying towards nest
Oh, maybe Dad has something for us!
2020-06-27
© Allison J. Gong

The second parent lands on the nest. . .

Parent barn swallow on nest containing nestlings
We want more!
2020-06-27
© Allison J. Gong

. . . and promptly takes off again. . .

Parent barn swallow leaving nest containing nestlings
Alas, no luck this time
2020-06-27
© Allison J. Gong

. . . leaving the babies alone in the nest again.

Three nestling barn swallows showing yellow gapes
Hungry nestling barn swallows
2020-06-27
© Allison J. Gong
Three nestling barn swallows
2020-06-27
© Allison J. Gong
Three nestling barn swallows
2020-06-27
© Allison J. Gong
Three nestling barn swallows
2020-06-27
© Allison J. Gong

These babies still need to grow feathers, although they are clearly big enough to thermoregulate without a parent sitting on them. Growing feathers takes a lot of metabolic energy, and aside from when the parents arrive with food the nestlings will sleep. But it's funny. They seem able to keep an eye (or maybe an ear) out for the parents flying around, and whenever one flies past the doorway they all perk up and start cheeping. There are lots of swallows at the marine lab right now, and I wonder if these babies can identify their parents from among all the other adults in flight.

They'll grow fast, being fed frequently by their parents. They'll have to get big and strong, to prepare for their migratory trip south in the fall I've never noticed exactly when they leave, I think because by the time they head south they've dispersed from the nest site. I always look forward to their return in the spring, though.

Published on Leave a comment on Felicitous cleavages

This morning as I was doing my rounds at the marine lab I noticed a pile of eggs next to one of the bat stars (Patiria miniata) in a large table. Somebody, or more likely, multiple somebodies, had spawned overnight. I have absolutely zero time to deal with another ongoing project right now, but I have even less self-control when it comes to culturing invertebrate larvae. So I sucked up as many of the eggs as I could, along with a fair amount of scuzz from the bottom of the table, and took a look.

Assortment of bat star (Patiria miniata) embryos
Embryos of the bat star Patiria miniata, about 1 day old
2020-06-19
© Allison J. Gong

As I've come to expect with stars, the early embryonic stages are developing asynchronously. There were unfertilized eggs (obviously not going to develop at all), zygotes that hadn't divided yet, and other stages.

  • Zygote
  • 2 cells
  • 16 cells
  • Many cells
Embryos of the bat star Patiria miniata, at various stages of development
2020-06-19
© Allison J. Gong

The coolest thing, though, will take some explaining. Animals begin life as a zygote, or fertilized egg. The zygote undergoes a number of what are called cleavage divisions, in which the cell divides but the embryo doesn't grow. A logical necessity of these two facts is that the cells get smaller and smaller as cleavage continues.

Now let's go back to the earliest cleavage divisions. One cell divides into two, each of those divides into two, and so on. The cell number starts with 1 and goes to 2, then 4, then 8, then 16, and so on. The process is more or less the same for all animals, but in only a few can these divisions be easily seen. Many echinoderms have nice distinct cleavage divisions and transparent-ish embryos, which is why the old-school embryologists in the early 1900s studied them.

Echinoderms are the major phylum in a group of animals called the deuterostomes. Incidentally, chordates (ahem--us) are also deuterostomes. The word "deuterostome" refers to the fact that during development in these animals the anus forms before the mouth does. That's right, folks, you had an anus before you had a mouth.

Another feature that is generally associated with the deuterostomes occurs in early cleavage. Picture this: A cell divides into two cells. Then each of those divides, resulting in four cells. Geometry dictates that the four cells form a plane. That makes sense, right? When the four cells divide again to make the 8-cell embryo, a second plane of cells is formed on top of the first. The second tier can either sit directly on top of the cells of the first tier (radial cleavage) or be twisted 45º so that the cells sit in the grooves between cells in the first tier (spiral cleavage).

Take a look at this embryo. Do you think it has undergone spiral cleavage or radial cleavage?

8-cell embryo of Patiria miniata
8-cell embryo of Patiria miniata
2020-06-19
© Allison J. Gong

This is a textbook example of radial cleavage. In all the sea urchin embryos I've watched over the years, I've never seen radial cleavage as clear and unambiguous as this. It was one of those moments when you actually get to see something that you've known (and taught) about forever.

So yes, echinoderms and other deuterostomes generally undergo radial cleavage. And I will hopefully have larvae to look after again! They will probably hatch over the weekend. On top of everything else that's going on now, additional mouths to feed are the last thing I need. But fate dropped them into my lap and who am I to argue with fate?

Published on Leave a comment on Becoming badass

Every year we are fortunate to watch a pair of red-tailed hawks (Buteo jamaicensis) raise young in a tree across the canyon. We're not always sure if the parents are the same birds every year, and I think this year's female is a different bird from last year. Her mate may be the male who has used this nest site for a couple of years now, but again, we don't know.

This year the parents raised three youngsters, who have just begun leaving the nest. They prepare for their first flights by making their way to the edge of the nest and flapping their wings to exercise the flight muscles. This is usually fun to watch, as they don't seem to care whether or not a sibling is in the vicinity. This flapping activity begins before the bird is fully feathered, and they look like awkward punk-rocker teenagers, trying to be cool and not even close to pulling it off.

The hawk nest is in a eucalyptus tree. As the time to fledge approaches, one or both of the parents often perches at the top of a nearby cypress tree. Usually the youngsters' first flights are to the cypress tree. Cypress trees may be the ideal location for fledging, because they have lots of soft-ish branches to fall on when the birds biff the landing. The first flights don't go far from the nest, and the birds end up hopping along branches as they flap their wings. So they are called branchers.

With raptors, the females are bigger. Males tend to leave the nest before their sisters, who have more growing to do, so we always assume that the first one to depart is a boy. This year the females lagged by only a day or so behind their brother. And all three of them seem to be progressing pretty quickly, compared to cohorts we've watched in previous years. Good little branchers!

Pair of sibling red-tailed hawks (Buteo jamaicensis), or branchers
2020-06-12
© Allison J. Gong

We watched these two for a while in the early evening. I don't know where the third one was. The branchers watch their parents soar around effortlessly. Here they are at the very top of the cypress tree:

Pair of sibling red-tailed hawks (Buteo jamaicensis), or branchers
2020-06-12
© Allison J. Gong

Okay, my digiscoping skills need work. I did, however, get lucky enough with the spotting scope and my phone to catch a few video clips.

You can see them trying to maintain their footing as the wind blows the tree around. They're able to use their wings for balance, but then they catch a little lift and get knocked about. In the second clip one of the birds is hanging out when its sibling crashes into it. If they were human teenagers, you'd hear one yelling "Look out below!" while the other hollers "Get off me!" Yeah, landing is toughest part of flight!

Over the next few weeks the branchers will get better and better at landing, and their flights will get longer. They will learn how to find thermals and soar. Their parents will continue to provide food for them, but at some point the kids will learn how to hunt on their own. Rodents of the neighborhood, look out! Eventually the branchers will be as badass as their parents. Then they'll disperse to find territories of their own.

Published on Leave a comment on Making babies

Every year, in June, my big whelk lays eggs. I have a mated pair of Kellettia kellettii living in a big tub at the marine lab. I inherited them from a lab mate many years ago now, and they've been nice pets. They've lived together forever, and make babies reliably. As June rolls around I start looking for eggs. This year I want to document the entire process, from egg-laying to larval development. Fortunately, I had the foresight to photograph the parents in May, as I didn't want to disturb the female once she began laying.

Female (left) and male (right) whelks (Kellettia kellettii)
2020-05-18
© Allison J. Gong

The female is significantly larger than the male. I know the big one is the female because that's the one that lays the eggs. I've never managed to catch the whelks copulating, but given the female's track record they either copulate regularly or she is able to store sperm for a long period of time.

In any case, she started laying eggs today. I went in to check on them and there she was!

Female whelk laying eggs
Female whelk (Kellettia kellettii) laying eggs
2020-06-12
© Allison J. Gong

I know from previous years that it can take over a week for the female to lay her entire clutch of eggs. Each of those pumpkin seed-shaped objects is an egg capsule, containing a few dozen embryos. The newly lain capsules are white, as you see above, and will gradually get darker as the embryos develop into larvae. The mother will lay the eggs and then depart. When the larvae are ready to leave the capsule, a small hole will wear through in the top of the capsule and the larvae will swim out. More on that later, hopefully.

I took some time-lapse video of the female, and was able to record her moving over the egg capsules and then leaving. I'd also put some food in the tub, and I think she got distracted.

I think it's really cool to see how well the snail can swivel around on her foot. Snails are attached to their shell at only a single point called the columella, the central axis around which the shell coils. Some snails can extend quite far outside the shell, and they can all pull inside for safety. The dark disc on the back of the foot is the operculum that closes up the shell when the snail withdraws into it.

Tomorrow when I check on things at the lab I'll see if she has resumed laying.

%d bloggers like this: