I had seen the sea lettuces (Ulva spp.) spawning in these high pools at Franklin Point before, and usually cursed the murkiness of the water. But today the water was dead calm, with the tide low enough that there were no waves to slosh into the pools. The result was a gorgeous marbled swirl in the water. The patterns were stunning.
What these photos show is the Ulva releasing either spores or gametes. Without microscopic examination it's impossible for me to know whether these tiny cells are spores or gametes. What I can say is that the spawn is released from the distal ends of the thallus, making the body of the alga look ragged.
The parts of the thallus that have already spawned are now clear. The tissue itself will soon disintegrate, leaving behind only the healthy green parts, which should be able to regrow.
All of these photos were taken in pools where the spawning itself had either completely or mostly stopped. Obviously when the tide comes back all of this yellow spooge will get mixed up. It's only when the water is perfectly still that these streams would form. It was hard stepping around the pools to take the photos, as the last thing I wanted to do was stomp my big booted foot into a pool and disrupt the beautiful patterns. Fortunately the sun angle was a little cooperative this morning, and I was able to find a pool where active spawning was happening.
What appears to be an act of destruction—the alga's brilliant green thallus being reduced to yellow streaks that drift away with the tide—is really an act of procreation. This is terminal reproduction, literally the last thing an organism does before it dies. Salmon do this, as do annual plants. The sheer amount of algal spawn in these tidepools is astounding. Imagine the number of 2-micron cells needed to color the water to this degree. But if reproducing is the last thing you're going to do in your life, you might as well go all in on your way out, right?
Intact shells are a limited resource in the rocky intertidal. Snails, of course, build and live in their shells for the duration of their lives. A snail's body is attached to its shell, so until it dies it is the sole proprietor of the shell. Once the snail dies, though, its shell goes on the market to whoever manages to claim it. Empty shells tend not to remain on the market for long.
Hermit crabs also live inside snail shells. They are the ones that compete for empty shells when they do become available. Here in California, at least, the hermit crabs can't kill snails for their shells; they have to wait for a snail to die. And once a shell comes on the market, it will have a taker even if it's not the ideal size for the crab. It's not at all uncommon to see hermit crabs that can fit only their abdomen into the shell, leaving the head and legs exposed and vulnerable. On the other end of the spectrum, many hermit crabs are so small that they can pull into the shell and not be seen by an inquisitive tidepool visitor. Anybody taking a snail shell home as a souvenir—where such takes are allowed, of course—must be certain that there is no tiny hermit crab hiding deep in the depths.
From a hermit crab's perspective, the best shell is one that is big enough to retreat into but light enough to be carried around. Snail shells come in a variety of shapes and corresponding internal volumes. Turban snails, with their roughly spherical shape, have a large interior space and are coveted by larger hermit crabs. For example, the grainy hand hermit crab (Pagurus granosimanus) seems to really like both black and brown turban snail shells.
Original inhabitant and builder of the shell:
And opportunistic second inhabitant of the same type of shell:
Other snails are not even remotely spherical. Olivella biplicata, for example, is shaped like the pit of an olive. Unlike Tegula, of which both intertidal species are found in rocky areas, O. biplicata burrows in sand. Note the shape and habitat of this olive snail:
These olive snails have a smaller internal volume, and thus tend to house smaller hermit crabs. Young individuals of P. granosimanus can be found in olive snail shells, but they quickly outgrow the cramped quarters and need to find a larger home. Smaller hermits such as Pagurus hirsutiusculus, though, are often found in olive shells.
Any hermit crab that finds itself robbed of its snail shell has a short life expectancy. The front end of the hermit resembles the front end of any crab, with the familiar armored legs, claws, eyestalks, and antennae. But the abdomen is soft and unarmored, covered by only a thin cuticle. The abdomen is coiled to follow the coiling of the snail shell, which allows the crab's body to curl around the columella, the central axis around which the shell spirals. In this way the crab can hang onto its snail shell and resist a tug by a would-be predator. A strong enough tug, though, will rip the crab's front end (head + thorax) away from its abdomen. So if you ever find yourself with a hermit crab in hand, do not be tempted to remove it from its shell by yanking it out!
The next time you encounter gastropod shells in the tidepools and want to know whether the inhabitant is a snail or a hermit crab, watch to see how it moves. Hermit crabs scuttle, as crabs do, while snails glide along very slowly. You would also notice a difference as you pick up the shell: snails stick to the rock with their foot, which you will feel as a suction. Hermit crabs don't stick at all, so if the shell comes away easily it likely houses a crab instead of a snail. See? Easy peasy lemon squeezy!
Sometimes even a well-known site can present a surprise. Here's an example. Yesterday I went up to Davenport to scope things out and see how the algae were doing. This is the time of year that they start growing back after the winter senescence. I also took my nature journal along, hoping to find a spot to sit and draw for a while.
The first thing I noticed was the amount of sand on the beach. Strong winter storms usually carve sand off the beaches, making them steeper. And during the calmer months of summer the beaches are flatter and less steep. Yesterday the beach was very thick and flat. It makes trudging across the sand in hip boots much easier!
The accumulation of sand meant that I could walk around the first point. Unless the tide is extremely low, such as we see around the solstices, the water is too deep for that. But yesterday I walked around it, and it wasn't until I got to the other side that it occurred to me that: (1) hey, I walked around the point; and (2) I could do that only because there was so much sand. See, a thick beach with a lot of sand makes a mediocre low tide feel lower because the water isn't as deep as it would be if the beach were thinner. When the tide isn't low enough for me to walk around the point, I have to clamber down a cliff. The cliff height varies depending on how much sand has built up, obviously, but is about head height for me. Getting down usually involves scooting on my butt and hoping my feet land on something that isn't slippery. As with most climbing, up is easier and less scary than down.
It's hard to imagine the amount of sand there was yesterday. Look at this picture.
See how the rocks in the foreground end? Usually that's the edge of the cliff. Yesterday I could have just taken a tiny step off the top of the cliff onto sand. That's over 1.5 meters of sand in that one spot! If the couple in the background were visiting this area for the first time, they'd have no idea of the conditions that made it so easy for them to get out onto the reef.
There was a lot of sand in the channels between rocks, too.
Normally those channels are deeper. You can see that some anemones were able to reach to the surface of the sand, but many more are buried, along with any other critters and algae unfortunate enough to be attached to the lower vertical surfaces. And while some of them will either suffocate or be scoured off as the sand washes away, many will survive and be ready to get on with life.
The second surprise of the day was a bright orange object. What I could see of it was about as big as my thumb, and at first I thought it was a nudibranch. Then when I crept closer for a better look, what popped into my head was "snailfish". Which was an odd thing, because I'd never seen a snailfish before. But something about the creature's posture looked somehow familiar.
Fortunately I had the presence of mind to take photos before trying to draw this little fish, because this is all I had time to get:
When I spooked the critter it took off really fast, confirming that it was no nudibranch. It was, indeed, a snailfish! It came to rest in a small hole in a rock, from where it looked out at me.
The snailfishes are a very poorly studied group. As a group they are related to the sculpins. There are snailfishes throughout the northern temperate and polar regions, from the intertidal to the deep sea. iNaturalist shows 43 observations of L. florae, eight of which are in California. Before yesterday, none had been recorded at Davenport Landing.
So there you have it, a snailfish! We don't know much about any of the snailfish species, even the intertidal ones. They apparently have pelvic fins modified to from a sucker, similar to the clingfishes, but I didn't have a chance to examine this specimen closely enough to confirm that. I don't know why they are called snailfishes, either. They're not snail-shaped at all.
Now, about that thing up there where I said "snailfish" came to mind even though I'd never seen one before. That happens quite a bit—a name will jump into my head before I've had a chance to think about it. Sometimes I'm wrong, but often I'm right. I know I hadn't seen a live snailfish before, but obviously I'd seen photos of them or I wouldn't have been able to recognize this orange creature as being one. It's fascinating how the brain forms search images, isn't it?
During what has become my daily check to see what's going on in Younger Lagoon, I got totally lucky and was able to see and photograph lots of birds. A morning with mostly cloudy skies meant good light for picture-taking. So I took lots of pictures! Some of these are series and need to be viewed in order to see the action. Sure, I could have just shot videos, but where's the fun in that? Sometimes still photos show a lot more than video.
It was a great day to watch wading birds! Legs and beaks come in varying lengths, and a particular species' combination of beak length and leg length determine where and how the bird forages.
While the long-billed curlew (N. americanus) has the longest beak-length-to-head ratio of any bird, the marbled godwit and whimbrel also have impressively long bills. In the photo below, the three birds with slightly downcurved beaks are whimbrels (Numenius phaeopus) and the one bird with the two-toned straight beak is the godwit (Limosa fedoa). Most of the godwits I've seen have beaks that are a smidge upturned, but this one looks pretty straight to me.
All of these birds forage by probing the sand with their beaks. All sorts of infaunal invertebrates are taken, and the mole crab Emerita analoga is a favored prey item. Obviously a longer beak allows for deeper probing in the sand, and the variation in beak lengths among the shorebird species may allow for niche partitioning. In other words, a long-billed curlew can reach down for prey items that are unavailable for birds with shorter beaks. The flip side of this equation is that birds with the "short" beaks might be better at picking up prey buried that are buried at shallow depths.
Prey are also distributed patchily along the beach itself, from the surf zone to the dunes, and these birds forage in the entire range. The length of the legs determines how far down into the surf zone they can go. When the beach is steep, as it is now at Younger Lagoon, the birds don't have much time to dig around in the surf zone before the next wave comes up. Click through the slide show to see this group of godwits, curlews, whimbrels, and a snowy egret react to an oncoming wave. It's important to note that while these birds do have some waterproofing in their feathers, they do not swim. Nor can they take flight if their feet aren't on the ground. Getting swept up by a wave and carried off the beach would likely be deadly for them.
The long-billed curlew is a favorite of mine, because I can't imagine what it would be like to go through life with a 2-meter beak sticking out of my face. They are fun to watch, and can probe remarkably fast with that long beak. This is one of the phenomena that is best shown by video.
You can watch how the birds forage within the surf zone, as in the slide show above, and also how long-billed curlews probe the sand higher up the beach.
These long-legged wading birds also feed in protected bodies of water and estuaries. All of these species can be seen at Elkhorn Slough as well as on the open coast, as one would expect from the Slough's position along the Pacific Flyway. Some birds migrate to California from far away. Marbled godwits, for example, spend the summer breeding season in the interior regions of North America, and winter along the Pacific, Gulf of Mexico, and Atlantic coasts. The long-billed curlew also breeds in the interior of the continent. Snowy egrets, on the other hand, are year-round residents.
I am grateful to have access to places like Younger Lagoon, where I can spend time outdoors without other people around, remove my mask, and take pictures of birds. I love that the Younger Lagoon Reserve has so many different habitats to explore, from ocean to beach to dunes to coastal scrub, in a small area. Fingers crossed that sooner rather than later, we'll be able to once again bring students there to study the natural world in the Reserve's outdoor classrooms.
On the penultimate day of 2020 I met up with my goddaughter, Katherine, and her family up at Pigeon Point to have two adventures. The first one was to find a marble that had been hidden a part of a game. We got skunked on that one, although the marble was found after we left and the hider had sent an additional clue. The second adventure was an excursion to the tidepools. I've had a lackadaisical attitude towards the afternoon low tides this winter, not feeling enthusiastic about heading out with all of the people and the wind and having to fight darkness. But the invitation to join the marble hunt, on a day with a decent low tide, meant that I could spend a good deal of quality time with Katherine.
It is not unusual for a promising low tide to be cancelled out by a big swell. It happens, especially during winter's combination of afternoon lows and occasional storms. The swell yesterday was pretty big.
Here's the view to the north, from Pigeon Point:
All that whitewash breaking over the rocks is not good for tidepooling, especially with small kids in tow.
This is how things looked to the south of the point:
This is Whaler's Cove, a sandy beach that lies on the leeward side of the point itself. See how the water is much calmer? It's amazing how different the two sides of the point are, in terms of hydrography, wind, and biota. The south side is much easier to get to, especially for newbies or people who are less steady on their feet. Being sheltered from the brunt of the prevailing southbound current means that the biological diversity is, shall we say, a bit subdued when compared to what we see on the north side of the point.
I first took Katherine tidepooling when her sister, Lizzie, was an infant riding in her mom's backpack. Katherine was about four at the time. Her mom and I were suprised at how much she remembered. She recognized the anemones right away, even the closed up cloning anemones (Anthopleura elegantissima) on the high rocks. She remembered to avoid stepping on them—that's my girl!
She wasn't all that keen on touching the anemones, though, even after we told her it feels like touching tape.
She did like the sea stars, too. Purple is my favorite color and I think hers, too, so the purple and orange ochre stars were a hit. It was nice to see two large healthy ones.
I had some actual collecting to do, so it was a work trip for me. Late December is not the best time to collect algae, but I wanted to bring some edible seaweeds back to the lab to feed animals. We haven't had any kelp brought in since the late summer, and urchins are very hungry. They will eat intertidal seaweeds, though, and when I go out to the tidepools I bring back what I can. It will be a couple of months until we see the algae growing towards their summer lushness, but even a few handfuls of sea lettuce will be welcome to hungry mouths.
Katherine and I walked up the beach for a little way to study one of the several large-ish crab corpses on the sand. This one was a molt rather than an actual corpse.
Katherine found the missing leg a little way off, and we discussed why we call these limbs legs instead of arms. "They use their claws to pinch things, like hands," she said. Not wanting to get into a discussion of serial homology and crustacean evolution with a 6-year-old, I told her that calling the claws "hands" isn't a bad idea, since they are used a lot like the way we use our hands. But, I continued, the crab walks on its other limbs like we walk with our legs, so can we call those legs? She was happy to agree with that. I can tell I will have to be careful about how I explain things to her, so that she doesn't come up with some wonky ideas about how evolution works.
In the meantime, Lizzie, the little sister, was having a grand old time. She flooded her little boots without a complaint and, after her mom emptied the water from them, squelched happily along with soggy socks. That girl may very well grow up to be a marine biologist!
Once the sun went behind the cliff it started getting cold. With one child already wet we decided to head back. On our way up the beach we saw this thing, which I pointed out to Katherine:
"What is it?" she asked. When I asked what she thought it was she cocked her head to one said and said, "It looks like a rock." Then I told her to touch it, which she didn't want to do. So I picked it up and turned it over, to show her the underside:
These big gumboot chitons do look more interesting from this side, because you can at least see that they are probably some kind of animal. Katherine had seen some smaller chitons on the rocks, so she had some idea of what a chiton is, but these are so big that they don't look anything like the ones we showed her earlier. Plus, with their shell plates being covered with a tough piece of skin and invisible, there are no outward signs that this bizarre thing is indeed a chiton. Katherine was not impressed.
At this time of year, when the sun decides to go down it goes down fast. But as we were walking back across the rocks the tide was at its lowest, so there was more terrain to explore. Then it was back up the stairs to the cars, where we could get warm and dry.
Oh, and Katherine and her mom and sister were able to find the hidden marble! They also hid one of their own for someone else to find.
As I write these words, a massive and powerful wildfire is raging through the Santa Cruz Mountains, approaching the city of Santa Cruz from the north and west. This morning's stats:
63,000 acres burnt/burning
1157 people fighting the fire (roughly 10% of what is needed to fight a fire of this size)
firebreaks constructed to protect the city and university
firefighters coming from out of the area and out of state
Much of the terrain burning is redwood forest. Big Basin Redwood State Park has burnt extensively. All park buildings and campgrounds have been severely damaged if not destroyed. Up the coast from me at Waddell Creek, the fire burned all the way to the ocean. Rancho del Oso, the nature center at the bottom of Big Basin at Waddell Creek, is in the middle of the forest; I don't know whether or not it still stands.
Each of these leaves tells the story of the destructive power of Nature. Most of them are from tanoak trees (Neolithocarpus densiflorus) or California bay laurel (Umbellularia californica), both of which are very common understory trees in redwood forests. For the past week, charred leaves have been tossed by updraft and carried along the wind, to be deposited miles away. Fortunately they are no longer acting as live embers when they touch down.
My camera gear is all packed up, in case we need to evacuate. I took these photos with my phone when I went to the marine lab this morning. They are completely unaltered. If they look a little too orange, well, that's how everything looks right now.
Why did I feel compelled to take these pictures? I think it's because the damage to Nature caused by Nature should be acknowledged as well as the damage to human lives, homes, and health. What I'm about to say may sound insensitive. I do not want to diminish the human tragedy of lost homes, livelihoods, and health. But I do want to shift my personal focus a little bit, because dwelling on all that has been and could be lost only renders me unable to function. If I can think about the future, perhaps even the long-term future far beyond my own life, I feel more grounded and ready to deal with the now.
What is and has been happening to the redwood forests is absolutely tragic. But the redwoods themselves are fire-adapted and resilient. The forest will recover. Already there are Facebook groups organizing to help the residents who have been displaced, begin the long and arduous process of cleaning up once the fire crews give the okay to do so, and start thinking about long-term monitoring of the forest's recovery. From a purely ecological perspective, it will be fascinating to document the process of secondary succession.
But before any of that can happen, human safety is the top priority. We are far from the end of this ordeal. While the weather has cooperated the past couple of days, with cooler temperatures and higher humidity thanks to the return of the marine layer, the forecast calls for 20-30% chance of lightning weather Sunday through Tuesday. That means more lightning strikes and more fires starting. We were visited by a firefighter yesterday afternoon, who told us that while we were not in the immediate evacuation zone we need to be ready to go. She advised us to do the usual fire prevention stuff—clear out a defensible space around the house, make sure there's no leaf litter or debris on the roof, etc. So we did. And now we stay indoors as much as possible, as the air quality outside is dismal. And we wait.
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.
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.
And of course algae are often the dominant inhabitants in the intertidal.
When bare rock isn't available, intertidal creatures need other surfaces to live on. To many small organisms, another living thing may be the ideal surface on which to make a home. For example, the beautiful red alga Microcladia coulteri is an epiphyte that grows only on other algae. Smithora naiadum is another epiphytic red alga that grows on surfgrass leaves.
We describe algae that grow on other algae (or plants) as being epiphytic (Gk: epi "on" + phyte "plant"). Using the same logic, epizooic algae are those that live on animals. In the intertidal we see both epiphytic and epizooic algae. For many of them, the epizooic lifestyle is one of opportunism--the algae may not care which animal they live on, or even whether they live on an animal or a rock. Some of the epiphytes, such as Microcladia coulteri, grow on several species of algae; I've seen it on a variety of other reds as well as on a brown or two (feather boa kelp, Egregia menziesii, immediately comes to mind). Smithora naiadum, on the other hand, seems to live almost exclusively on the surfgrass Phyllospadix torreyi.
Animals can also live as epiphytes. The bryozoan that I mentioned last time is an epiphyte on giant kelp. Bryozoans, of course, cannot move once established. Other animals, such as snails, can be quite mobile. But even so, some of them are restricted to certain host organisms.
The aptly called kelp limpet (Discurria insessa), lives only on the stipe of E. menziesii, the feather boa kelp. Its shell is the exact same color as the kelp where it spends its entire post-larval life. Larvae looking for a place to take up a benthic lifestyle settle preferentially on Egregia where adult limpets already live. It's a classic case of "If my parents grew up there it's probably a good place for me."
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.
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.
Tecturapalacea 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.
Cute little thing, isn't it? Tectura palacea seems to have avoided being the focus of study, as there isn't much known about it. Ricketts, Calvin, and Hedgpeth write in Between Pacific Tides:
A variety of surfgrass (Phyllospadix) grows in this habitat on the protected outer coast; on its delicate stalks occurs a limpet, ill adapted as limpets would seem to be to such an attachment site. Even in the face of considerable surf, [Tectura] palacea, . . . , clings to its blade of surfgrass. Perhaps the feat is not as difficult as might be supposed, since the flexible grass streams out in the water, offering a minimum of resistance. . . The surfgrass provides not only a home but also food for this limpet, which feeds on the microalgae coating the blades and on the epithelial layers of the host plant. Indeed, some of the plant's unique chemicals find their way into the limpet's shell, where they may possibly serve to camouflage the limpet against predators such as the seastar Leptasterias hexactis, which frequents surfgrass beds and hunts by means of chemical senses.
And that seems to sum up what is known about Tectura palacea. There has been some work on its genetic population structure, but very little about the limpet's natural history. The intertidal is full of organisms like this, which are noticed and generally known about, but not well studied. Perhaps this is where naturalists can contribute valuable information. I would be interested in knowing how closely the populations of T. palacea and Phyllospadix are linked. Does the limpet occur throughout the surfgrass's range? Does the limpet live on both species of surfgrass on our coast? In the meantime, I've now got something else to keep my eye on when I get stranded on a surfgrass bed.
I'm not the world's most diligent user of iNaturalist, but I do try to upload observations after I've been tidepooling or hiking or poking around outdoors. The other morning I did go to to the intertidal, for only the second low tide series since the COVID quarantine began. State park beaches were closed over the Independence Day holiday weekend, to all except people who could walk there. This rather limited my options, but it was fine because I hadn't been to Natural Bridges in quite a while. It's a site I know well, so I also used the trip to record some video clips to use when I teach Marine Biology in the fall.
My favorite iNat observation for the day is this one:
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.