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!
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:
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!
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 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
And because, like me, John had a special affinity for the anemones:
And he would have loved this. What is going on here? How did this pattern come to be?
And look at this, three species of Anthopleura in one tidepool! Can you identify them?
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.
And even though I'm not very good at finding nudibranchs, even I couldn't miss this one. It was almost 4 cm long!
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:
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.
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.
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.
Sometimes we can even find Pisaster doing both at the same time:
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.
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.
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.
Animal associations can be strange and fascinating things. We're used to thinking about inter-specific relationships that are either demonstrably good or bad. Bees and flowering plants--good. Mosquitos on their vertebrate hosts--bad. In many cases the 'goodness' or 'badness' of these associations is pretty clear. However, there are cases of intimate relationships between animals of different species that cannot be easily categorized as good or bad.
Take, for example, the barnacles on the skin of gray and humpback whales. From the barnacles' perspective the skin of a whale isn't a bad place to live: as the whale swims through the water the barnacle is continually flushed by clean water, which should make feeding easier. But is the whale affected in any way by its barnacle passengers? I suppose they might increase the drag coefficient a little bit and make swimming marginally less efficient, and maybe they itch, although it's hard to imagine that the whale would really care much one way or the other.
A week ago I went to the intertidal up at Pigeon Point. It's a great spot for certain animals, especially the small six-rayed stars of the genus Leptasterias. These stars rarely get larger than 8 cm in diameter and always have six arms. I've been told by a friend who just happens to be a sea star taxonomist at the Smithsonian, that making species identifications in the field is very difficult for this genus, so I've stopped trying. I do know that some of the Leptasterias stars have slender rays and others have thicker rays.
The most common large star at Pigeon Point is the bat star, Patiria miniata. These stars get about as big as my outstretched hand, and come in a variety of colors. Last week I didn't see very many Patiria, but all of them were reddish orange, like this one:
Unless they're so abundant as to be annoying, I like picking up bat stars and looking at their underside. That's because sometimes they have these little dark squiggles in their ambulacral groove:
That little squiggle is a polychaete worm, Oxydromus pugettensis. It is one of many polychaete worms that forms a symbiotic relationship with another animal species. Some symbiotic polychaetes live in the tubes of other worms, or within the shells of bivalves, for example. Oxydromus crawls around inside the ambulacral groove of Patiria, where it feeds on scraps of leftover food from the star's meals. The worms don't like light, and as soon as I picked up this star and flipped it over the worm started burrowing down between the star's tube feet to get back to the dark. The next day I found another star with a worm and was able to take a picture of it before it disappeared.
Oxydromus pugettensis is clearly segmented, evidence of its annelidan roots. It doesn't look very different from many other free-crawling polychaetes. A member of the family Hesionidae, it lives in fine silty sediments in the intertidal as well as in the ambulacral grooves of sea stars. According to one source, it is the most common intertidal member of its family along the California and Oregon coast. For reasons as yet undetermined, P. miniata seems to be the favored host, although I have also seen the worms in the ambulacral grooves of the leather star Dermasterias imbricata.
Over two days at Pigeon Point last week I examined a total of five bat stars, and all of them had worms. One of the stars had three worms! It's possible that more worms were hiding deep within the ambulacral grooves, too. I always wonder how, in this type of association, the partners manage to find each other. How does one "lucky" star end up with three worms? Do the worms every migrate from one star to another? Does the star do anything to attract the worms? In what way(s) would the star benefit from having a few worms in its ambulacral regions? It does seem that the worms don't stick around very long once a star is brought into the lab--I don't know if they die or just leave on their own--but since they also live in the sand maybe they do actively migrate between stars. There hasn't been much work done on these worms in recent decades, probably because of the overall decline in natural history studies. However, I'll keep this worm in mind for my Marine Invertebrate Zoology students this fall, when one of them asks me for help coming up with an idea for his or her independent research project.
It has been a few weeks since I posted about my most recent batches of urchin larvae. Some strange things have been happening, and I'm not yet sure what to make of them. It would be great if animals cooperated and did what I expect; somehow that never seems to be the case. The upshot of all this uncertainty is that there is always something new to learn. I, for one, am not going to complain about that.
One noteworthy thing to report is that my hybrids all died, very quickly and unexpectedly. They had been racing through development and on the dreaded Day 24 they looked great.
And the next time I changed their water, they were all dead. So much for the hybrid vigor I had written about earlier. Teach me to get cocky and think I know what's going on.
Fast forward to Day 52, and some of the cultures are still going strong. I originally set up four matings, and at least some individuals from each are alive. One thing that seems to happen when I start multiple batches of larvae at the same time is that the batch with the fewest numbers does the best. This time my F3xM1 mating was always the least dense culture, but some of them have already begun and completed metamorphosis. And the ones that are metamorphosing are the ones being fed what I expected to be the less desirable food source. As I said, not much of this whole experience is making sense.
The good thing is that I have an opportunity to observe these larveniles in action. As long as they don't get arrested in this neither-here-nor-there stage, they should soon join their siblings as permanent inhabitants of the benthos.
This video contains short clips of three different larveniles. I've arranged the clips from earlier to later stages of metamorphosis. Although these are three separate individuals, you can imagine that each one goes all of these stages.
Having both tube feet (for crawling around the benthos) and ciliated bands (for swimming in the plankton) make these animals unsuited for either habitat. They have gotten very heavy and sink to the bottom, but it doesn't take much water movement to knock them off their five little tube feet. It always amazes me that teensy critters like this, so fragile and easily killed, manage somehow to stick in the intertidal and survive long enough to be grown-up urchins on their own. And yet some of them will. I've seen it happen.
A few days ago I was in the intertidal with my friend Brenna. This most recent low tide series followed on the heels of some magnificently large swells and it was iffy whether or not we'd be able to get out to where we wanted to do some collecting. Our first day we went up to Pistachio Beach, just north of Pigeon Point, where the rocky intertidal is bouldery and protected by some large rock outcrops.
So while the swell was indeed really big, we were pretty well protected in the intertidal. The Seymour Center has a standing order for slugs, hermit crabs, and algae. I was easily able to grab my limit (35) of hermit crabs over the course of the afternoon, and while it's too early in the season for the algae to do much I had my sluggy friend with me to take care of finding nudibranchs, which left me free to let my attention wander as it would.
The very first thing to catch my eye as we go out there was the coenocytic green alga Codium setchellii, which I wrote about last time. I've seen and collected C. setchellii from this site before, but don't remember seeing it in such large conspicuous patches. I need to review what I learned about the phenology of various intertidal algae, but here's a thought. Maybe Codium is an early-season species that gets outcompeted by the plethora of fast-growing red algae later in the spring. Red algae were present at Pistachio Beach but not in the lush (and slippery!) abundance that I'll see in, say, June. I'm willing to bet that Codium will be less abundant in the next few months.
In my experience, the six-armed stars of the genus Leptasterias have always been the most abundant sea stars on the stretch of coastline between Franklin Point and Pescadero. Even though they are small--a monstrously ginormous one would be as large as the palm of my hand--they are very numerous in the low-mid intertidal. I've seen them in all sorts of pinks and grays with varying amounts of mottling. Alas, I don't know of any really reliable marks for identifying them to species in the field.
Unlike other familiar stars, such as the various Pisaster species and the common Patiria miniata (bat stars), which reproduce by broadcast spawning their gametes into the water, Leptasterias is a brooder. Males release sperm that is somehow acquired by neighboring females and used to fertilize their eggs. There isn't any space inside a star's body to brood developing embryos, so a Leptasterias female tucks her babies underneath her oral surface and then humps up over them. Leptasterias also humps up when preying on small snails and such, so that particular posture could indicate either feeding or brooding.
Here's a Leptasterias humped up on a rock, photographed last spring:
The only way to tell if a Leptasterias star is feeding or brooding is to pick it up and look at the underside. I did that the other day and saw this:
Those little orange roundish things are developing embryos. While the mother is brooding she cannot feed, and can use only the tips of her arms to hang onto rocks. Don't worry, I replaced this star where I found her and made sure she had attached herself as firmly as possible before I left her. In a few weeks her babies will be big enough to crawl away and she'll be able to feed again.
Looks like the reproductive season for Leptasterias has begun.
The next day Brenna and I went to Davenport, again hoping to get lucky despite another not-so-low tide and big swell.
Davenport Landing Beach is a popular sandy beach, with rocky areas to the north and south. The topography of the north end is quite variable, with some large shallow pools and lots of vertical real estate to make the biota very diverse and interesting. The big rocks also provide shelter from the wind, a big plus for the intrepid marine biologist who insists on going out even when it's crazy windy. The southern rocky area is very different, consisting of flat benches that slope gently towards the ocean, with comparatively little vertical terrain. The southern end of the beach is always more easily accessible, which is why I almost always go to the north. But this day the north wasn't going to happen. The winter storms had washed away at least a vertical meter of sand between the rock outcrops. That and the not-so-low tide combined for conditions that made even getting out to the intended collecting site a pretty dodgy affair. So Brenna and I trudged across the beach to the south.
Along the way we saw lots of these thumb-sized objects on the beach. At first glance they look like pieces of plastic, but after you see a few of them you realize that they are clearly (ha!) gelatinous things of biological origin. They are slipper-shaped and you can stick them over the ends of your fingers. They have a bumpy texture on the outside and are smooth on the inside.
Any guesses as to what they are?
These funny little things are the pseudoconchs of a pelagic gastropod named Corolla spectabilis. What is a pseudoconch, you ask? If we break down the word into its Greek roots we have 'pseudo-' which means 'false' and 'conch' which means shell. Thus a pseudoconch is a false shell. In this case, 'false' refers to the fact that this shell is both internal (as opposed to external) and uncalcified.
The animal that made these pseudoconchs, Corolla spectabilis, is a type of gastropod called a pteropod (Gk: 'wing-foot'). Pteropods are pelagic relatives of nudibranchs, sea hares, and other marine slugs. They are indeed entirely pelagic, swimming with the elongated lateral edges of their foot. Like almost all pelagic animals, Corolla has a transparent gelatinous body. Even their shell is gelatinous, rather flimsier than most shells, but it serves to provide support for the animal's body as it swims.
You can read more about Corolla spectabilis and see pictures and video here.
Why, you may be wondering, do the pseudoconchs of C. spectabilis end up on the beach, and where is the rest of the animal? The body of Corolla and other pteropods is soft and fragile. When strong storms and heavy swells seep through the area, the water gets churned up and pteropods (and other pelagic animals) get tossed about and shredded. This leaves their pseudoconchs to float on currents until they are either themselves demolished by turbulence or cast upon the beach. Corolla is commonly seen in Monterey Bay, and it is not unusual to find their pseudoconchs on the beaches after a series of severe storms.
Brenna and I were wondering if we could preserve the pseudoconchs somehow. I took several back to the lab and tried to dry them, thinking that they might behave like Velella velella does when dried. Unfortunately, the next day they had shriveled into unrecognizable little blobs of dried snot, and the day after that they had disintegrated completely into piles of dust. Maybe drying them more slowly would work. Something to consider the next time I run across pseudoconchs in the sand.
It has been almost three and a half years since I first documented seastar wasting syndrome (SSWS) in the lab. Since then many stars have died, in the field and in the lab, and more recently some species seem to be making a comeback in the intertidal. This circumstantial evidence may not be reason enough to conclude that the epidemic is over, but I think there is reason to be hopeful. Any disease outbreak eventually runs its course, and despite its death toll there are always at least some survivors. And I have an individual star that was very sick but seems to be recovering.
In September of 2015 one of my bat stars (Patiria miniata) developed the first tell-tale lesion of SSWS on its aboral surface. At the time the lesion was small (less than 10 mm in diameter) and superficial. Knowing that SSWS starts with minor symptoms and rapidly progresses to something horrific within a day or so, I wanted to keep an eye on this star. It held the same morbid fascination as a car accident or any other impending catastrophe.
5 September 2015
24 November 2015
By November 2015 the main lesion hadn't grown much but a few others had developed. The star still wasn't acting sick and was eating every once in a while, although it occasionally ignored the food that I offered.
So far, so good. I was thinking that the star doesn't look too much worse, so maybe it wouldn't keep getting sicker. I checked on it regularly, offered food a few times a week, and left it alone.
4 May 2016
Several months later I noticed that the first lesion had gotten much deeper. The outer dermal layers had been completely compromised, exposing the animal's internal organs (gonad and digestive caecum) to the external environment. This was bad, very bad. Even in stars, internal organs are supposed to be internal, except when stars extrude their stomachs to feed.
This was the point in time when things started going south. The star lost the ability to maintain its internal turgor pressure and became lethargic and floppy. It stopped eating, or even responding to food. It spent most of its time in a corner of the seawater table where it lives, although a few times I saw it wrapped around one of the hoses that feeds the table. However, its body never started disintegrating the way I'd seen with other SSWS victims.
19 January 2017
Fast-forward another several months. About a month ago the sick bat star began perking up a bit when I placed food near the tip of one of the arms. A week later it actually wrapped its arm around the food, and I assume ate it. It has since been eating about once a week, after fasting for at least eight months. I began to think it would recover.
Today I had some time to photograph the star again, and it really appears to be doing much better!
The lesions are apparently healing over; at any rate, the internal organs are no longer exposed to the outside. The body margin between the arms has a few small divots, but they look superficial. Lately the star has been more active, too, cruising around the table instead of hunkering down in a corner. I'm going to keep feeding it to see if it continues to improve.
One of the most remarkable things about many animals with a decentralized nervous system, such as echinoderms and cnidarians, is their ability to regenerate lost parts and repair damage to their bodies. This bat star is a prime example. It has been sick for almost a year and a half now, and for at least half that time it hasn't eaten. Yet it somehow had the metabolic reserves to heal a major wound to its body wall. That's some astounding resilience there. I am very impressed, and you should be, too.
Sea urchins have long been among my favorite animals. From a purely aesthetic perspective I love them for their spiky exterior that hides a soft squishy interior. I also admire their uncanny and exasperating knack for getting into trouble despite the absence of a brain or centralized nervous system. Have you ever been outsmarted by an animal without a brain? I have. It's rather humbling.
Red sea urchins (Mesocentrotus franciscanus) and purple sea urchins (Strongylocentrotus purpuratus) share a common geographic range along the northeastern Pacific but generally live in different habitats. S. purpuratus is the common urchin in tidepools, while reds are almost always subtidal (although I have seen them in the intertidal on very low minus tides). The two species' habitats do overlap a bit, as the purple urchin can live in subtidal kelp forests alongside the reds. There is a commercial fishery for the gonads of red urchins, which are prized as uni by sushi aficionados. I've tried uni once, and it tasted exactly the way I imagined the gonads of a sea urchin would taste. Not a fan. I'd much rather make a different use of urchin gonads.
The other week I collected some urchins from the field, hoping that they'd have nice full gonads. Gametogenesis in many marine invertebrates, including sea urchins, is governed at least partly by annual light cycles. Provided they have sufficient food, purple urchins have ripe gonads and spawn in the winter, from December through March. Reds spawn in the spring, from March through June. In my experience the best time to induce spawning of purps in the lab is December or January, when the urchins have developed gonads but likely haven't spawned yet. There is no way of knowing the sex of any given urchin or the condition of its gonads, so this exercise is somewhat of a crap shoot even with the best of planning.
Today I shot up my eight field-collected purps, hoping to get at least one male and one female out of the deal. I got lucky with the timing, as one of the smallest urchins was a female and began spewing out eggs. This little female gave a lot of eggs! She was followed by three males and two more females. So out of my eight purps I ended up with three of each sex, and a spawning rate of 75% ain't bad.
I set up some mating crosses and fertilized all of the eggs. I divided the little female's eggs into two batches and fertilized them with the sperm of two different males (M1 and M2). Each of the other females' eggs was fertilized by M1, who gave huge amounts of sperm. When I checked on the eggs about two hours post-fertilization most of them had gone through the first cleavage division and seemed to be developing normally and on schedule.
Just for the hell of it I decided to shoot up some of the red urchins we have in the lab. I didn't really think they'd spawn, as it's not the season for them to be gravid. Red urchins are large, heavy animals with long and sharp spines and they are much more difficult to handle. Four of the five that I shot up did nothing, as expected. It took a long time, but just as I was about to give up on them the biggest red began dribbling out a couple thin streams of sperm. I examined the sperm under the microscope and they were very active and healthy. Fortunately I hadn't returned the purps to their tanks, and two of the female were still putting out some eggs. I rinsed the purp eggs into a clean beaker, pipetted up some of the red sperm, and added it to the eggs.
Sea urchin eggs are covered by a thick jelly coat. In the video you can see many of the red urchin sperm embedded in the jelly coat of the egg. Despite the frantic activity of the sperm, fertilization (as evidenced by the rising of the fertilization envelope off the surface of the egg) took much longer than it does when eggs and sperm come from the same species.
Look at that beautiful zygote! Fertilization success in this hybrid cross was low, only about 50%. The eggs that did get fertilized went through the first cleavage division after about two hours later, which is right on time.
It remains to be seen whether or not the few hybrid embryos I have continue to develop. I have a colleague who has hybridized red and purple urchins successfully in the past, and has raised the offspring to adulthood. I don't have any expectations of great success with this little experiment, but it would be very informative to raise known hybrid urchins. I've seen animals in the field that look like hybrids and there's no reason to assume that hybridization between these two free-spawning species never occurs. The adults can be found living side-by-side subtidally, and there's enough overlap in their reproductive seasons that some individuals of each species could very well spawn at the same time. On the other hand, hybridization that can be forced in the lab doesn't necessarily occur in the field. I dumped a lot of red urchin sperm on those purple urchin eggs, and such high sperm concentration may overcome any mechanisms of reproductive isolation that exist under real-life conditions.
Well, we can't—at least, not very well. I suppose we can eat it in small amounts, but sand itself is one of the most nutrient-poor substances imaginable. Sand is, after all, ground up bits of rock. It would provide certain minerals, depending on the type of rock, but none of the essential macronutrients—carbohydrates, proteins, and lipids—that animals need to survive.
When I was a kid I thought that sand dollars were called sand dollars because I'd find their broken tests on sandy beaches. I knew they lived in sand, hence the name. As I started studying marine invertebrates in college I learned that sand dollars don't just live in the sand; they also eat sand. In addition to organic matter, usually in the form of detritus, sand dollars eat sand to create ballast. This makes them heavy and keeps them from being picked up and carried away by waves. It is also why, if you come across an intact sand dollars test and break it open, sand will fall out of it.
I have a batch of recently settled Dendraster excentricus, the common sand dollar in northern California. They began metamorphosing only 30 days post-fertilization. As the larvae settled and transformed into tiny sand dollars, I decided to try to figure out what to feed them. These animals aren't grown commercially and there doesn't seem to be a definitive answer on how to raise them. One of the suggestions I got was "Well, we know they eat sand, so feed them sand."
Which is what I did. The first time I just sprinkled a bit of sand in the dish with the juvenile sand dollars. Then I looked under the microscope to see that the sand grains were about 10 times the size of the animals. Oops. But the sand dollars didn't look unhappy so I let them be. I decided that they also needed something organic to eat so I ground up a small piece of Ulva and dropped some of the resulting slurry on them.
The second time I offered sand to the sand dollars I ground it up in a mortar and pestle that I scrounged from the lab next door. Let me tell you, grinding sand makes a sound that is every bit as horrible as you imagine. At least it produced smaller particles that the sand dollars might be able to eat. I continued to offer Ulva mush in addition to the fine sand. If they end up eating either sand or Ulva, I can provide that pretty easily. The question is, how do I know whether or not they're eating?
How many sand dollars can you find in the above photo? They are exactly the same color as the sand. I don't have real proof that these little guys are eating sand; even their poops would look like the sand. The animals do tend to clear the space in their immediate vicinity, but I think that might be due to the action of the tube feet and spines rather than consumption of either sand or Ulva. In this video clip you will see that the sand dollars are very active, even though all the motion doesn't seem directed the way it does in urchins at this stage.
They do a lot of waving around, but don't actually walk. They do, however, seem to like being tilted up a bit, similar to the way adult sand dollars position themselves when in calm water:
I do have circumstantial evidence that my sand dollars are eating something. The first ones metamorphosed at 30 days post-fertilization. Today is day 51 post-fertilization, which means some of the animals have been post-larvae almost as long as they were larvae. I know it takes about a week for newly metamorphosed sea urchins to form their new guts and begin feeding, and I assume it's the same for sand dollars. In fact, because these sand dollars raced through larval development so quickly I expected their juvenile mouths to break through quickly as well. If this were the case, then these animals should have had complete and functional guts for almost two weeks now. The fact that they're not dead or dying makes me think that they have to be eating.
Call it a hunch, call it intuition, call it wishful thinking. I'm not sure how they're doing it, but I think they're fine. Next week I hope I can find time to measure them.
And I don't mean plague as in "too many stars to know what to do with," but as in "disastrous sickness that you don't want to catch." Some of the stars in my seawater table have been succumbing to some awful disease lately. A week ago today I noticed that many stars had been busy cannibalizing one of their compadres. Sometimes this just happens, and it doesn't necessarily indicate that things are about to go south. But when I looked more closely I noticed that the victim, instead of just being eaten, had autotomized its arms. Autotomy occurs in most sea stars and other invertebrates, and in fact is used as a method of clonal replication in some stars and many cnidarians. The species of star that is being affected by this plague (Pisaster ochraceus, the common ochre star) isn't one that readily autotomizes except in response to some external stress, such as a predator pulling on an arm.
So something was going on in this table. On Monday (Labor Day) I popped in for a quick check and although nobody had lost any arms I couldn't be absolutely sure that everything was okay. Some of the Pisasters were a little squishy and had arms that were a little twisted. On Tuesday morning there was no autotomy but in the afternoon a star had lost an arm, greatly disturbing the student lab assistant who discovered it. On Wednesday the table looked like an asteroid battlefield:
Many of the other Pisasters were also showing signs of sickness: curly arms (visible in the yellow star in the lower right corner of the photo above. Another ominous sign is that some of the apparently sickly stars were kind of squishy, indicating that the water vascular systems were somehow compromised.
Severed arms littered the table. The autotomized arms retain mobility for quite a while after being cast off--they literally don't know that they're dead.
After removing the corpses and cleaning the table as best I could I was able to take a closer look at the survivors. I noticed that most of the remaining Pisaster stars had twisty or crossed arms, and some showed pretty severe stretching in the interambulacral area ("armpit" between adjacent rays), which I think is the first stage of autotomy.
The disease progresses very rapidly, and within an hour a star in this condition had pulled off one arm and was working on another.
Unfortunately, this disease also affects other species. My Orthasterias koehleri (rainbow star) decided to join the fun. When I arrived Wednesday morning it was intact. It dropped an arm. I went away for about 40 minutes to take care of tasks in a different building, and when I returned it had lost two more arms:
Alas, my one and only Orthasterias succumbed later in the day and was dead on Thursday. Interestingly, the disease does not seem to affect either Patiria miniata (bat stars) or Dermasterias imbricata (leather stars). In fact, the Patiria have been eating pretty well over the past week, scavenging on the carcasses of the plague victims. I don't know if eating the diseased tissue will cause problems later on.
On Friday I lost two more Pisasters and isolated the Patiria and Dermasterias into tanks. A colleague of mine calls this the Molokai treatment, and I probably should have done it sooner, but I figured that at this point all the stars in the table were exposed to whatever pathogen is causing this disease so at that point why bother? However, I will need to sequester the healthy stars in order to disinfect the table once the disease has run its course, so into tanks they went.
After checking on the stars Saturday morning I am cautiously optimistic that the plague may have run its course. One more Pisaster, that was looking sickly the day before, had died, but my last two appeared healthy. Their arms were not curly, I didn't see any interambulacral stretching, and they felt nice and hard when I poked at them. All of these are good signs, but I will continue to keep close watch on them. If they make it to Monday we just might be out of the woods.
As of today, one week after I noticed the first severe symptoms, I have lost 80% of my Pisaster collection. To put that in to context, this mortality rate is every bit as bad as some villages that were virtually wiped out by the medieval Black Death.