At this time of year low tides occur in the afternoon. Later in the spring they will shift to mornings. There are a few reasons that I really prefer morning low tides to those that occur in the afternoon: (1) the time of the low gets about 50 minutes later every day, so as the tide series progresses you start fighting loss of daylight; (2) the wind tends to pick up in the afternoon, making it colder and causing ripples on the surface of pools that make it difficult to see; (3) the intertidal is more crowded with human visitors on the afternoon lows. I had decided to use today’s low tide to photograph a particular clump of barnacles at Natural Bridges, and figured that it would be a quick trip because all the extraneous human activity would get on my nerves.
Turns out I found my barnacle clump pretty quickly, but it had been overgrown with tube worms (Phragmatopoma californica) and I wasn’t sure I could see the trait that I was looking for.
At least, I’m pretty sure I was in the right spot, looking at the same barnacles I’d seen in January. In any case, this year for whatever reason we have a bumper crop of Phragmatopoma. They are very abundant and appear to be expanding their range within the intertidal. Somebody should be keeping an eye on that. Ahem.
It was a beautiful afternoon, so when I had finished taking photos for “work” I sat around to bask in the sun and watch the surf.
As I sat quietly, the animals got used to my presence and went about their business as if I weren’t there. To me this is one of the best things about being in nature, the opportunity to disappear and watch animals do their thing without being noticed.
After this bird cooperated so nicely, I challenged myself to catch as many different bird species in a single photograph. I got three in a single frame, twice:
Pelicans are so cool. Their populations were hit hard by DDT but have recovered beautifully in recent decades. To watch them skim the waves is one of life’s great pleasures. But my favorite photo of all the pelicans I shot today was this one of a pelican against the afternoon sky:
The luck with birds didn’t stop when I left the beach, either. As I was walking back I came across a great blue heron (Ardea herodias) standing so still that at first I thought it was a statue even though I knew there wasn’t a statue in that spot.
When all was said and done, it ended up being a good afternoon. I got my attitude adjusted, saw some cool stuff, and left the intertidal feeling better than I did when I arrived. Thank you, Mother Nature, for the much-needed trip outside myself and opportunity to get my head straight.
While much of America was glued to the television watching a football game, I went out to the intertidal at Davenport Landing to do some collecting and escape from Super Bowl mania. The Seymour Center and I have a standing agreement that some animals–small hermit crabs and certain turban snails, for example–are always welcome, which gave me an excuse to look for them. I also needed to pick up some algae for labs that I’m teaching later this week, so it was an easy decision to be alone in nature for a couple of hours.
As usual, I was easily distracted by the animals, especially the anemones. They are simply the most photogenic animals in the rocky intertidal. And we have an abundance of beautiful anemones in our region; I feel very lucky to photograph them where they live. I would like to share them with you.
Along the central California coast we have four species of anemones in the genus Anthopleura. Two of them, A. xanthogrammica and A. sola, are large and solitary; in other words, they do not clone. The geographic ranges of these two species overlap in central California. Anthopleura xanthogrammica has a more northern distribution, from Alaska down to southern California, while A. sola typically lives from central California into Mexico.
I’ve seen these congeneric anemones living side-by-side in tidepools at Natural Bridges and at Davenport. Here is a photograph from yesterday. The animals are almost exactly the same size, and are separated by about 30 cm. Can you tell which is which?
The pièce de résistance yesterday was a treasure trove of Anthopleura artemisia anemones. I’d seen and photographed them several times before, and always appreciated the variety of colors they come in. For some reason, though, yesterday they really caught my eye. I had a number of “Wow!” moments.
These stark white tentacles are new to me. The anemone measured about 4 cm across. In every other aspect it looks like A. artemisia, and I’m almost entirely certain that’s what it is. It does feel special to me. I will hopefully be able to keep an eye on this individual and see if its colorless tentacles are a temporary or long-term condition. And now that my eye has been primed to see the colors that A. artemisia comes in, I may notice more unusual color morphs.
One of the best things about teaching is the opportunity to keep learning. Case in point: yesterday I attended an all-day teacher training session for the LiMPETS program, so that I can have my Ecology students participate in a big citizen science project in the rocky intertidal later this spring. In the Monterey Bay region LiMPETS is organized and run out of the Pacific Grove Museum of Natural History, where yesterday’s training took place. LiMPETS has two ongoing citizen science projects, one looking at populations of mole crabs (Emerita analoga) on sandy beaches and the other monitoring population of several invertebrate and algal species on rocky shores. Of course, my interests being what they are I signed up for the rocky intertidal monitoring project.
We spent the morning learning about the history of the program and how to identify the organisms that are monitored, then after lunch went out to Point Pinos to collect some data and work through the process that we need to teach to our students. The day before we’d had a high surf advisory on the coast, and yesterday the swell was still big. We hiked out to the study site and set up the transect line, which runs from the top of a rock through the entire range of tidal heights to the low intertidal.
Where Emily is standing is about 10 meters along the transect line. The monitoring protocol calls for sampling at every meter on the transect. One of the other teachers, Phaedra, and I were the only ones wearing hip boots, so we volunteered to work at the lowest spot. We thought we’d start with the 10-meter quadrat and hopefully get down to the 11-meter quadrat once the tide receded a bit more. Then we got hit by a few big waves and decided that discretion is the better part of valor and gave up. It was a pretty easy decision to make, especially after the quadrat got washed away and we had to go fetch it when the waves brought it back.
All told the group collected eight quadrats of data. We had a little time to poke around (i.e., take pictures) before heading back to the museum for data entry.
Codium is an interesting alga. These cylindrical structures are composed of many filaments, which in turn contain multi-nucleate cells. Yes, the cells contain multiple nuclei. Codium fragile has the common name “dead man’s fingers,” I suppose because. . . well, I actually have no idea. As far as I can tell they don’t feel anything like a dead man’s fingers, or the way I imagine a dead man’s fingers would feel.
There were quite a few empty abalone shells scattered among the rocks. As we were hiking out I found this shell. When I tried to pick it up I found that it was still alive, and well stuck to the rock. This is a very good sign, as the black abs have been suffering from withering syndrome, in which the animal gradually loses its ability to hang on.
All in all, this workshop was a lot of fun. If I have to give up an entire Saturday to do training, it couldn’t get much better than spending at least part of it in the intertidal. And Point Pinos is such a fabulous intertidal site that I certainly wouldn’t turn down an opportunity to explore there again.
BEWARE: This is a mini-rant. Continue at your own risk.
Several times over the past year or so I’ve heard the term “king tide” being tossed about in the general media. I remember looking up the term when I first heard it, back in December 2014, and came across the following definition, which I cribbed from the EPA’s website: The king tide is the highest predicted high tide of the year at a coastal location. Okay, I thought then, every year there is going to be one highest high tide and why not call it a “king tide”? A king, after all, is the biggest of the cheeses, the headiest of the honchos, the top of the heap. I could live with that, although I generally steer clear of hokey terms and wouldn’t dream of using “king tide” in my classroom.
In 2015, however, it seemed that we heard about “king tides” about half a dozen times. WTF is up with that? Obviously, the highest tide of the year can’t occur more than once in a year, right? So why did I read reports of “king tides” in January, around Thanksgiving, and at Christmas last year? Part of the problem is that the meaning of the term itself has morphed into something else. Instead of reserving “king tide” for only the highest tide of the year, writers are now using it to refer to any old spring tide. I detest this trend the same way I detest grade inflation—it gives an ordinary natural occurrence more importance than it deserves and doesn’t make it clear what’s going on.
Okay then, let’s clarify.
First of all, what are spring tides, anyway?
Well, spring tides are the extreme low and high tides that we get every two weeks or so. Spring tides and the intervening neap tides, during which both low and high tides are of intermediate height, are due to the gravitational pull of the sun and moon on Earth’s water. Obviously the sun, being orders of magnitude more massive than the moon, has much more gravitational pull than the moon; however, the moon is much closer to the earth and has a much stronger effect on our tidal cycles.
The top of the figure above depicts what is going on during spring tides. During a new or full moon the gravitational pulls of the sun and moon are aligned, causing higher-than-average high tides (and correspondingly lower-than-average low tides). When the moon and sun are forming a right angle with respect to the earth their respective gravitational pulls cancel each other out a bit and result in intermediate high and low tides. These neap tides occur during the first- and third-quarter moon phases. Even people who don’t live near the ocean have experienced the different phases of the moon, and have some understanding that the lunar cycle is about 28 days long. Thus every month we can expect two cycles of alternating spring and neap tides.
Oh, and spring tides get their name from the fact that the tide level bounces up and down like, well, a spring. And the amplitude of the tides increases and decreases throughout the month, as does a spring when you pull it, let it settle, and then give it another pull.
The take-home message is that EVERY MONTH we have extreme high and low tides. You could even say (though I certainly wouldn’t) that we have a “king tide” every month, since one of the high tides is going to be the highest of the month. Kinda takes the oomph out of the phrase, doesn’t it? What’s the fun of being a king if there are 11 other kings? Nobody gets to be THE king, which is kind of the whole point of being a king in the first place, isn’t it?
So what are the reporters trying to convey?
Digging a little deeper into pages from NOAA and other reputable sites, I think the intended message is that the effects of ordinary spring tides will be augmented by El Niño and climate change. Such effects include increased coastal erosion and flooding. When a spring high tide coincides with a big storm surge, which has happened here in Santa Cruz the past couple of days, the threat of flooding becomes quite real. The National Weather Service issued a high surf advisory for yesterday and today. The surf was indeed big when I went out to check things at the marine lab this morning.
In the context of a spring high tide combined with a big storm-driven surge, I can live with the term “king tide,” although I still don’t like it and won’t use it myself. A tide is a tide and has specific direct causes; same with a storm surge. Mixing them together and slapping the label “king tide” on the conflation gives people the wrong impression of what’s going on and implies that somehow the tide and the surge are the same thing. They are not; they are two independent phenomena that occasionally happen at the same time, that’s all. I am an educator and it’s my job to impart scientific information in both academic and informal settings. But I feel that my job is made more difficult when the media get all hyped up about an impending king tide and either state or imply that it will be the highest high tide of the year, and then we read about it again a few months later, and yet again during the following spring tide series. It’s both bogus and lazy.
The new moon is tonight, which of course means that we are in spring tides. Yesterday afternoon my friend and colleague Scott joined me for my first visit to the intertidal in 2016. And where to go for this inaugural field excursion of the new year, but to Franklin Point? Low tide was at 15:53 yesterday, so we met up at 14:00, stopped to fill up the gas tank, and headed up the coast. Expecting it to be crazy windy as afternoons tend to be on the coast, I had dressed in extra layers. Scott and I were surprised to emerge from the car and find it wasn’t windy at all, so even though the air temperature was cool at least we didn’t have to deal with any significant amount of windchill factor.
Hiking over the dunes we saw Unusual Thing #1–a bridal photo shoot. A couple of stretches of the trail are covered by a boardwalk, and on the first of these we encountered a bride decked out in full regalia–wedding dress, flowers, hair, make-up–and two photographers. They were very nice and let us pass through in our decidedly inelegant boots and field gear. I didn’t think it would be very nice to take their picture. However, I did think that they’d lucked out and gotten a great day for photography: the aforementioned lack of wind meant that the bride wasn’t freezing in her slip of a wedding dress, and the afternoon light was flat so there were no shadows or harsh glare.
Descending onto the beach we came across Unusual Thing #2–an elephant seal.
It is e-seal haul-out time at Año Nuevo State Park a few miles down the road from Franklin Point, and I’ve seen them on the beach a few times before. This was the first time I’d seen an adult male, though, and he was HUGE! Without being stupid and going over to stand next to this animal it’s hard to depict how large he is, and unfortunately there wasn’t anything in the vicinity to give a sense of scale. So trust me, or look it up for yourself, male elephant seals are ginormous. This big guy was taking a siesta, and we could hear him snoring. He did wake up and lift his head to look at us, but we gave him plenty of room as we walked past and he returned to his nap.
One of the reasons I wanted to see Franklin Point after the El Niño storms of the past week was to see how much sand had been washed away from the beach. Sand typically accumulates on California coastal beaches during the dry storm-less months of summer and autumn, only to be flushed away by storms the following winter. After a particularly violent storm or a series of storms occurring in a short time, very large amounts of sand can be removed from a beach. For the past four years we haven’t had much of a winter storm season (hence the awful drought) and the beach at Franklin Point has been tall and gently sloped. I’d grown accustomed to this state of affairs, which makes what we saw yesterday qualify as Unusual Thing #3–rocks that had been covered with sand for years and are now exposed.
To set the stage, here’s a picture that I took on an afternoon low tide last year on 17 March 2015:
Can you see how much steeper the beach is in yesterday’s photo? And those rocks on the left side? They are not visible in the photo from last spring because they were under sand!
You can see exactly how high the sand was last summer. What’s really exciting is that these rocks represent pristine habitat that has yet to be exploited. I can look at primary ecological succession this spring! Well, at least until the sand returns and buries the rocks again.
As we meandered among the rocks in the intertidal, Scott and I both noticed an abundance of abalone shells. Fairly early on we spotted this black ab shell lying emersed above the water line:
We were actually surprised to see that the animal was alive. Healthy living abalone are firmly attached to rocks, tucked into crevices. This one wasn’t attached to anything, just lying on the sand. We picked it up, turned it over, and found the body of the animal shriveled up and filling up only about half of the space it should have occupied. It didn’t respond to gentle pokes but wasn’t dead yet, or at least not dead enough to pass the stink test for deadness.
Withering syndrome is a bacterial disease that inhibits digestive function in abalone. To stave off starvation the infected animal begins to digest its own body tissues. As a result the entire body shrinks and eventually the foot can no longer stick to rocks. In California it affects black abs and red abs (H. rufescens). Until the recent years of warmer-than-usual water black abs (H. cracherodii) had been most common in southern California, but I’ve been seeing more of them in the past few years. Now it looks like the disease that plagues them has accompanied them up the coast. It’s not surprising, given the current El Niño conditions.
This gives me another thing to keep an eye out for in my intertidal excursions. I’ll start keeping track of abalone and see if withering syndrome becomes more prevalent. Might as well start with this afternoon’s low tide!
About two and a half months ago, the ongoing disaster of sea star wasting syndrome raised its ugly head again when one of my bat stars (Patiria miniata) developed lesions on its aboral surface. Here’s what it looked like then:
See how the lesion is sort of fluffy? It looks as though tissue may be sloughing off the surface. Wanting to see how the syndrome would progress, I let it remain in its table and kept an eye on it. Every so often I took it out and examined it, and nothing really seemed to change. The animal continued to eat, retained its internal turgor pressure, and none of its table mates became sick. Eventually I sort of forgot about it.
Until two of my students last week asked if I had any pictures of sick sea stars that they could borrow for their end-of-the-semester project. This question jump-started my brain and I remembered this particular bat star, and told the students they could come to the lab and take their own pictures of it. . . that is, if it were still alive. They were able to visit me this past Monday and together we looked at the animal.
Lo and behold! it’s not dead, and actually looks pretty good.
The star has a few pale areas in addition to the original lesions, but overall doesn’t seem sick at all. It’s nice and firm, righted itself quickly when we placed it in the bowl with its oral surface up, and crawled around very actively.
Not only that, but take a closer look at the lesion itself:
The lesion appears to be somewhat sealed off, as if the epidermis has recovered. I gently poked the surface of the lesion with my forceps, and it feels a little firm and nothing squirted out of or peeled off the surface of it. I think it’s analogous to a scab that forms over a skinned knee. Of course, while a scrape on my knee would heal after a few days, sea stars have a much slower metabolism so I’m not really surprised that it would take over two months for this individual to show signs of a healing lesion.
Of course, I could be entirely wrong about what’s going on with this lesion. It’s the same size as it was back in September, so I’m not convinced that it’s healing. However, it seems that closure of the wound is better than a wide-open gaping sore that leaves the animal’s innards exposed to the external environment. If, over the next several weeks the edges of the wound begin to come together, then I’ll be more confident that this animal is on the road to recovery. In this season on Thanksgiving, this is something to be grateful for.
You may have heard that earlier this month the California Department of Fish and Wildlife postponed the scheduled opening of the commercial Dungeness crab season. Gasps of dismay were heard all over the state from Californians whose Thanksgiving traditions include cracked crab, as well as from the folks who make a living fishing for them. The closure is due to the detection of domoic acid (DA) in the crabs. DA is a naturally occurring toxin produced by some species of diatoms in the genus Pseudo-nitzschia. DA is ingested by filter-feeding animals such as mussels, and due to the process of bioaccumulation occurs in higher concentrations in the tissues of animals that feed at higher trophic levels. Humans can be affected by DA also, which is why state officials warn people not to collect and eat mussels when DA levels are high enough to be concerning.
Since the crab fishery closure I’ve been wanting to do my own informal assessment of Pseudo-nitzschia in the water, but with one thing and another I didn’t have the time or opportunity until today. This morning I collected a plankton sample and gave myself a few hours to play with it before I had to start grading papers. Pseudo-nitzschia was present but not incredibly abundant, especially compared to what I saw this past August. Today’s Pseudos were in chains of 3-4 cells, instead of the 12 cells that were common in the summer.
But it turns out that Pseudo-nitzschia wasn’t the most interesting thing I found in the plankton today. Just about at the time that I was supposed to stop playing and start grading, I saw one of these:
This was a big cell, measuring 250 µm long and 80 µm wide. Right away it had a diatom look about it: the visible protoplasm was golden-brown, the color of diatoms; it didn’t have any cilia or flagella; and it was scooting along very slowly, the way a pennate diatom does. But it wasn’t anything that I recognized, which made it all the more intriguing. I made an executive decision to investigate further, even if it meant not getting my papers graded. Damn the consequences, science was calling!
I did some poking around, searching through photo databases of local diatom species, not having much success. Since this was a new (to me, at least) critter, it warranted not just a photo and video but an entry in my real lab notebook:
Besides, spending time with a microscope, notebook, and pencil feels more like doing science than when I take pictures. And it has been a while since I’ve been entirely stumped, so I was having fun.
It turns out that this diatom isn’t all that uncommon in Monterey Bay. I happened across a report of a diatom named Tropidoneis antarctica that had been detected in a plankton tow off our very own Santa Cruz Wharf about a week ago. BINGO! I had a name for my mystery critter, learned something new, and got to play for a morning. And notice that I spelled the genus name wrong in my notebook? Oops.
And, by the way, the papers did all get graded. I am (un)fortunately far too responsible to have let them not get graded. I’m working on that, though. Give me another 50 years or so and I’ll be as flaky and unreliable as the next guy.
A few weeks ago I made a pilgrimage to the Great Tidepool in Pacific Grove, where Ed Ricketts did much of his collecting in the 1920-40s. Ricketts is a legend among students of the intertidal here in California, but he is known to a much wider audience as the inspiration for the character Doc in John Steinbeck’s novels Cannery Row and Sweet Thursday. Steinbeck and Ricketts were good friends, and in the spring of 1940 the two of them hired a seiner out of Monterey and her captain and crew for a six-week trip to collect intertidal invertebrates from the Sea of Cortez. The journal from that trip, published in 1951 as The Log from the Sea of Cortez, is a classic work of biology, philosophy, and adventure–one of my all-time favorite books and a definite recommended read.
For my birthday, I was treated to a tour of the Pacific Biological Laboratories on Cannery Row in Monterey. This is where Ricketts lived and worked. The original building on this site was completely destroyed in late 1936 by a fire that began at an adjacent cannery; Ricketts managed to escape with his typewriter but lost almost all of his collections, research notes, and scientific library. Fortunately for posterity, Ricketts’ book on intertidal ecology, Between Pacific Tides, had already been sent to the publisher. Ricketts rebuilt his home and lab, which is the building that currently occupies the site. The city of Monterey provides free docent-led tours of the Lab on the second Saturday of every month.
I was primarily interested in Ricketts the scientist, although Ricketts the music-lover, poet, and philosopher was also discussed in the tour. We did get to see the building and back yard, including what the docent referred to as the “holy of holies,” Doc’s lab itself.
I love this old stuff, even though I probably don’t want to know what was in any of these jars. Nor do I really want to be able to read the label on this bottle (okay, yeah, I really do):
I imagine that all the hazardous stuff was removed once the building became a museum, but the romantic in me wants to believe that these bottles still contain some essence of the work that went on in this room. Besides, I’ve encountered bottles that appear to be of not-much-younger vintage in old labs, and while they’re undoubtedly scary they are also fascinating.
This is the very desk that Steinbeck and Ricketts purchased to take on their voyage to the Sea of Cortez. Unfortunately, they hadn’t measured the berths on the boat they hired, and the desk didn’t fit anywhere. It spent the entire voyage lashed down and covered with a tarp.
Ricketts’ back yard holds a big rusted boiler that he used to render the livers of basking sharks (the smell must have been ungodly awful), as well as a series of concrete basins that he used as holding tanks for the animals he collected. The Pacific Ocean breaks literally against what would have been his garden wall if he’d had a garden.
Visiting this place made me aware that I hold a teensy bit of Ricketts’ legacy in my hands whenever I teach about marine invertebrates or marine ecology. I certainly don’t have Ricketts’ poetic way of writing about these animals, but I hope that my students come away with a glimmer of what I love about them. And that I can be a conduit through which Ricketts’ holistic view of the world he observed is transferred to another generation of naturalists. It’s a big job, but somebody’s gotta do it.
Today my most recent batches of urchin larvae are six days old. Yesterday being Monday, I changed their water and looked at them under the scopes. I was pleased to be able to split each batch into two jars, as the larvae have already grown quite a bit; I now have a total of four jars to take care of. This makes me inordinately happy. Having only two jars is risky, as it wouldn’t take much for both of them to crash, but for some reason I feel more confident of success with four jars. It’s probably one of those all-your-eggs-in-one-basket things.
These larvae are perfectly formed. At this point they are shaped essentially like squared-off goblets, with four arms sticking up at the corners of the goblet. They will continue to grow arms in pairs until they have a total of eight (four pairs). The stomachs (the round-ish pale red structures in the middle of the body) are big and round; the color of the stomachs is due to the food that the larvae are eating. And can you see the skeletal rods extending into each of the arms? Each of the eventual larval arms will be supported by one of these rods, and additional rods will serve as cross-braces going horizontally across the body.
Ever wondered what these animals eat? In the wild they would be feeding on whatever phytoplankton they can catch. In the lab we have several types of phytoplankton growing in pure culture, but trial and error has taught us that urchin larvae do best on a diet of the cryptophyte Rhodomonas sp.
The red color of the cultures is due to the color of the cells. When the larvae eat this food their stomachs turn pinkish. Rhodomonas cells are about 25 µm long and have two flagella that they use to zip around. Here’s a short video of a drop of Rhodomonas culture on a slide:
They sort of look like sperms, but the cells are much larger than sperms, the flagella are much shorter than the single flagellum of a sperm, and their swimming isn’t quite right to be sperms, either.
The larvae themselves live in glass jars in one of the seawater tables that I converted into a paddle table. The larvae are negatively buoyant and would sink to the bottoms of the jars if left unstirred, and the gentle back-and-forth motion of the paddles keeps them, and their food, suspended in the water column.
See my four jars? They are a sign of short-term success. There’s still a lot of time for things to go south with these larvae, and I certainly don’t take for granted that I’ll be able to keep them alive for the duration. But today, as my students were dissecting urchins in lab, I was able to show them the offspring of said urchins. I hope to keep the larvae alive through the end of the semester, to show the students as much as I can of larval development in one of my favorite animals.
Having obtained decent-ish amounts of gametes from sea urchins, the next step is to get eggs and sperm together. The first thing I did was examine the spawned eggs to make sure they were round and all the same size. Lumpy eggs or a variety of sizes of eggs indicates that they are probably not fertilizable. These eggs from F1 looked just about perfect:
Note that the eggs are all similarly sized (80 µm in diameter) and round. These look good to go.
The next step is to dilute the sperm in filtered seawater and introduce a small amount to the eggs. The sperm need to be diluted because, believe it or not, in this case too much of a good thing is bad. There’s a phenomenon called “polyspermy” which is pretty much exactly what it sounds like: an egg being penetrated by more than one sperm. Polyspermy leads to wonky development down the road, and while it probably rarely happens in the field, where sperm would be diluted immediately upon being spawned, it definitely does occur in the lab. However, eggs are smart and have evolved a couple of mechanisms to prevent polyspermy.
The fast block to polyspermy occurs within a few seconds of the fusion of the sperm and egg plasma membranes. As the sperm nucleus begins to enter the cytoplasm of the egg, Na+ ion channels in the egg membrane open and cause a depolarization of the egg membrane; this depolarization makes the egg impenetrable to other sperm. However, the egg membrane cannot remain depolarized indefinitely, so after about a minute the slow block to polyspermy takes effect.
The slow block is the rising of the egg’s vitelline layer above the surface of the egg, creating what we call the fertilization membrane. This envelope acts as a physical barrier against additional sperm. The really cool thing about studying fertilization in sea urchins is that you can watch it happen in real time. I mean, how often do you get to observe the formation of a brand new life at the moment that is is being formed?
In this video there are 2.5 eggs in the field of view. Concentrate on the two whole eggs. The one on the top has already been fertilized, which you know because you can see the fertilization membrane surrounding it. You can also see a lot of sperm zooming around. Keep an eye on the lower of the whole eggs; can you see the rising of its fertilization membrane?
Of the two female urchins that spawned for me this morning, F2 had only a few eggs to give but her fertilization rate was 100%. F1, on the other hand, spawned a lot of eggs but only about 50% of them were fertilized. I have no explanation for this. Sometimes (quite a lot of times, actually) things simply don’t work.
That said, at our local ambient temperature the first cleavage division occurs about two hours post-fertilization. That’s when I saw this:
A few hours later the embryos had progressed to what I think is the 16-cell stage. At this point it starts getting difficult to distinguish the different cells without focusing up and down through the embryo. But if you know what you’re looking at, the three-dimensional structure does make some sense. In the embryo below I can talk myself into seeing two rings of eight cells each, one ring lying on top of the other.
If the embryo is at the 16-cell stage, then it has undergone four cleavage divisions. The early divisions of an embryo are called “cleavages” because the cells divide in half to form equal-sized daughter cells. In other words, the cell cleaves. During cleavage the embryo doesn’t grow, which means that the average cell size necessarily decreases. Cleavage divisions will continue for a total of about 24 hours, resulting in a stage called a blastula.
