It's no secret that I love pelicans. I love watching them soar low over the waves, where they are truly in their element. I love watching them plunge from the air into the water and then bob right back to the surface, because unlike their cormorant relatives, pelicans can't fly underwater. And I love watching them plunk around on land, where they are dumpy and awkward but still somehow elegant.
The other day I ventured out between storms to photograph birds. As per usual I ended up down at Natural Bridges, where pelicans were hanging out on the last remaining rock arch. They were well within the reach of my long lens, so I took a lot of photos.
The best photos I got were of a subadult pelican coming in for a landing.
Landing gear down!
Decreasing air speed:
And. . . touchdown!
A job well done!
The youngster managed a safe landing without knocking one of its compadres into the water. That isn't always the case--those wings can do a lot of damage. But the three adult birds on the left hardly seemed to notice, which means the youngster has learned how to stick the landing without disturbing everyone else in the vicinity. I'm sure that's a lot easier said than done!
The intertidal sculpins are delightful little fish with lots of personality. They're really fun to watch, if you have the patience to sit still for a while and let them do their thing. A sculpin's best defense is to not be seen, so their first instinct is to freeze where they are. Then, if a perceived threat proves to be truly frightening, they'll scoot off into hiding. They can also change the color of their skin, either to enhance camouflage or communicate with each other.
Around here we have a handful of sculpin species flitting around in our tidepools. Sculpins can be tricky to identify even if you have the fish in hand--many of the meristics (things you count, such as hard spines and soft rays in the dorsal fin, or the number of scales in the lateral line) used to distinguish species actually overlap quite a lot between species. The fishes' ability to change color means that skin coloration isn't a very reliable trait. When I was in grad school there was another student in my department who was studying the intertidal sculpins, and she told me that most of the ones we see commonly are either woolly sculpins (Clinocottus analis) or fluffy sculpins (Oligocottus snyderi). I've developed a sort of gut feeling for the gestalt of these species, but I'm not always 100% certain of my identifications.
Anyway, back to the camouflaged sculpins. The ability to change the color of the skin means that sculpins can match their backgrounds, which comes in very handy when there isn't anything to hide behind. Since the environment is rarely uniformly colored, sculpins tend to have mottled skin. Some can be banded, looking like Oreo cookies. The fish in this photo lives in a pool with a granite bottom. The rock contains large quartz crystals and is colonized by tufty bits of mostly red algae. There is enough wave surge for these fist-sized rocks to get tumbled about, which prevents larger macroalgae from colonizing them.
Other shallow pools higher up in the intertidal at Asilomar have a different type of rocky bottom. The rocks lining the bottom of these pools are whitish pebbles that are small enough to be tossed up higher onto the beach. I don't know whether or not these pebbles have the same mineral content as the larger rocks lower in the intertidal, but they do have quartz crystals. The pebbles are white. So, as you may have guessed, are the sculpins!
Other intertidal locations have different color schemes. On the reef to the south of Davenport Landing Beach, you will see a lot of coralline algae. Some pools are overwhelmingly pink because of these algae. Bossiella sp. is a common coralline alga at this location.
What color do you think the sculpins are in these pools?
Give yourself a congratulatory pat on the back if you said "pink"!
Sculpins aren't the only animals to blend in with coralline algae. Some crustaceans are remarkably adept at hiding in plain sight by merging into the background. Unlike the various decorator crabs, which tuck bits and pieces of the environment onto their exoskeletons, isopods hide by matching color.
Turning over algae and finding hidden creatures like these is always fun. For example, I saw these isopods at Pescadero this past summer. See how beautifully camouflaged they are?
Sometimes, when you're not looking for anything in particular, you end up finding something really cool. Last weekend I met up with students in the Cabrillo College Natural History Club for a tidepool excursion up at Pigeon Point. We were south of the point at Whaler's Cove, where a staircase makes for comparatively easy access to the intertidal.
It's fun taking students to the intertidal because I enjoy helping them develop search images for things they've never seen before. There really is so much to see, and most of it goes unnoticed by the casual visitor. Often we are reminded to "reach for the stars," when it is equally important to examine what's going on at the level of your feet. That's the only way you can see things like this chiton:
Mopalia muscosa is one of my favorite chitons. It is pretty common up and down the California coast. However, like most chitons it is not very conspicuous--it tends to be encrusted with algae! This individual is exuberantly covered with coralline and other red algae and has itself become a (slowly) walking bit of intertidal habitat. It is not unusual to see small snails, crustaceans, and worms living among the foliage carried around by a chiton. Other species can carry around some algae, but M. muscosa seems to be the most highly decorated chiton around here. I showed this one to some of the students, who then proceeded to find several others. A search image is a great thing to carry around!
Compared to the rocky intertidal, a sandy habitat can be a difficult place to live. Sand is inherently unstable, getting sloshed to and fro with the tides. Because of this instability there is nothing for holdfasts to grab, so there are many fewer algae for animals to eat and hide in. Most of the life at a sandy beach occurs below the surface of the sand, and is thus invisible to anyone who doesn't want to dig. There's a beach at Whaler's Cove where I've found burrowing olive snails (Olivella biplicata) plowing along just below the surface. I wanted to show them to the students, so I waded in and rooted around. I did find Olivella, but I also found a burrowing shrimp. I think it's a species of Crangon.
Now that is some damn fine camouflage! If the shrimp didn't cast its own shadow, it would be invisible. Even so, it was clearly uneasy sitting on the surface like that. I had only a few seconds to shove the camera in the water and snap a quick photo before the shrimp wriggled its way beneath the sand again.
As I've said before, observation takes practice and patience. To look at something doesn't mean you truly see it. That's why it is so important to slow down and let your attention progress at the pace of the phenomenon you're observing. If the only things that catch your eye are the ones that flit about, then I can guarantee you will never find a chiton in the intertidal. And wouldn't that be a sad thing?
Autumn is migration season in California. We all know that, in the northern hemisphere, birds fly south for the winter and return north for the summer. And indeed, this is a very good time to go bird watching along the Pacific Flyway, as migrating birds stop to rest and feed at places such as Elkhorn Slough. Here in Santa Cruz, autumn is punctuated by the return of monarch butterflies (Danaus plexippus), roosting in eucalyptus trees at Natural Bridges State Beach and Lighthouse Field.
Since 1997 the Xerces Society for Invertebrate Conservation has been tracking monarch sightings on their migrations between the western U.S. and Mexico. They conduct a volunteer butterfly count every Thanksgiving. More recently, community science data sources such as iNaturalist provide much of the information.
This morning, before it got warm, I went to Natural Bridges to see how the monarchs were doing. I wanted to photograph clumps of butterflies dripping from tree branches. It seemed, however, that there aren't as many butterflies as I remember from previous years. The clusters were not nearly as large or as dense as they should be. And the data shown in the figure below do demonstrate a precipitous decline in monarch since 2017. We're still a couple of weeks away from this year's Thanksgiving count, and there is still a chance that the butterflies might arrive in larger numbers.
Trained observers know how to estimate the number of butterflies in a cluster like this. The numbers of butterflies at various roosting sites are aggregated to assess overall population sizes.
This morning I did see one butterfly that had a tagged wing. It was wearing a green Avery round sticker, with some writing in what looks like black Sharpie. The color of the sticker was very close to the green of the surrounding foliage, so I wasn't even able to see the sticker until I downloaded the pictures from the camera.
At first I thought the tag resulted from an official scientific project or undertaking, but it turns out that anyone can tag a monarch. The tags are used to track migration of the butterflies. There doesn't seem to be a central depository of tags and their origins, so knowing the color of the tag doesn't tell me where this particular butterfly came from.
Once the sun hits the butterflies and they begin to warm up, the clusters start breaking apart. Butterflies open and close their wings, exposing the darker dorsal surfaces to the sun and warming up their flight muscles. Sometimes they dislodge one another.
On a cool morning like this, many of the butterflies that fell out of the clump couldn't fly yet, and landed on the ground. The boardwalk is perhaps not the safest place for a butterfly to wind up, but at least in a monarch sanctuary such as Natural Bridges the visitors are knowledgeable and look out for the butterflies' safety.
As I wrote before, the butterflies we see at Natural Bridges this year were not born here. This means that their survival to this point has depended on healthy conditions in the Pacific Northwest and the western slopes of the Rocky Mountains, where they lived as caterpillars and emerged from their chrysalises. This also means that planting milkweed for monarch caterpillars in California won't help the butterflies that we see here, although it would help butterflies that are destined to overwinter elsewhere. What will help local butterflies--monarchs and otherwise, and all nectar-feeding insects, in fact--is planting California native plants, to provide them with the nutrition they have evolved to survive on.
Sometimes dead things can be very informative. Not in the same way as their living counterparts, of course, but there are times when observing a dead specimen reveals details that cannot easily be discerned when the creature is alive. For example, most living birds don't let you get a close look at their feet. Dead birds, on the other hand, don't complain and try to maim you when you spread their toes and look for webbing. What does webbing have to do with anything? It tells you whether and how a bird swims, of course.
Cormorants are fish-eating predators. Like their relatives, pelicans, they do plunge-dive from the air into the water. However, cormorants are much more streamlined than pelicans and also chase their prey underwater. A bird locomoting in water has two options for propulsion--it can use its wings to "fly" underwater or use its feet to paddle along.
Take a look at the foot on that dead cormorant. It is clearly webbed, eminently suitable for a bird that uses its feet to swim underwater. The location of the feet also has functional significance. Note how far back they are on the bird's body. Obviously this helps increase the overall streamlining of the body. Now think about how submarines move through water: the prop of a submarine is also positioned on the back of the boat. That's probably not a coincidence.
Any trip to the beach brings opportunities to see creatures that have washed up. Or are in the process of washing up. Sometimes even (relatively) large animals end up beached. The big scyphozoan medusae, for example, have little control over where the currents take them, and find themselves in shallow water close to shore.
Animals made of jelly do not fare well when they encounter land. There were several of these dinner-plate-sized jellies drifting and pulsing lazily in very shallow water. A few had been left stranded by the receding tide and were already drying up. Even the ones that were still alive would probably never get back to deeper water. Fortunately for them, they are blissfully unaware of their imminent demise--sometimes lacking a centralized nervous system with its all-knowing brain would be a blessing.
Death, of course, is a part of life and a very important part of nature. Even knowing that, it can be disturbing to see dead animals washed up on the beach. For most people, the shells and whatnot of invertebrates don't seem to count as dead things, but everybody recognizes a dead bird. And there is a natural human tendency to feel sorrier for things that are more like us. From a biologist's perspective, keeping track of dead animals on beaches can give us a lot of information about conditions in the sea. There is a sort of standard death rate, but deviations above what is considered normal may signify that something is going on. There are volunteers who make monthly patrols along beaches in the Monterey Bay Area, collecting data on the various carcasses that wash up. These data are used to evaluate the overall health of the waters within the Monterey Bay National Marine Sanctuary. Knowing about dead things can teach us about what's going on with the living things.
People call them air rats or trash birds, but I really like gulls. Especially the western gull (Larus occidentalis), known colloquially among birders as the WEGU. Yes, gulls eat garbage, but that's only because humans are so good at making garbage and leaving it all over the place. Other gulls may travel quite far inland--in fact, the state bird of Utah is the California gull (Larus californicus)--but the WEGU is a California Current endemic species. This means that its natural food sources are the fishes and invertebrates of the California Current, which flows southwards along the west coast of North America. As a result, it lives in only a very narrow strip of coastline, nesting on cliffs and restaurant roofs.
Case in point. Yesterday afternoon I was at Moss Landing with my marine biology students. We had hiked along the road, over the dune to the beach, down the beach a ways, and returned over the dune to circle back to our starting point. The last item of note that we all watched was a western gull hunting along the shoreline of the Moss Landing harbor.
It had grabbed a crab. It looked like a rock crab, but I couldn't tell what species.
The crab wasn't dead, and was thrashing around enough to make it difficult for the gull to get a good grip on it.
The crab gets a reprieve!
But the gull didn't give up. It reached down, came back with the crab in its beak, and then flew off.
Last Wednesday, 23 October 2019, my marine biology students and I visited the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing. We were led through the facilities by Kim Fulton-Bennett, the PR officer. MBARI isn't generally open to the public, so this was a rare opportunity to peek behind the scenes at what goes on at this work-class institution.
We got to see whatever equipment the engineers and technicians had lying around. Outside we saw the top part of an instrument that had been removed from its buoy for routine maintenance.
One of the few personal items we saw was a certain mooring buoy. It was covered with messages and signatures to a man named Roman Marin. I knew him when he was a graduate student, and had taken a marine plankton course for which I was the TA. I ran into him a few years ago on a previous field trip to MBARI, and we chatted for a few minutes. Anyway, Roman died suddenly about a month ago. I remember hearing of his death and thinking how nice a guy he had been.
Here's Kim Fulton-Bennett showing us a sort of mini-rover called a MesoBot. Its job is to dive down to about 1500 meters, explore the mesopelagic, and relay information through a tethering cable back to the mother ship. It's a brand new robot, having been on a only one test dive so far.
And here are some top-down views of the MesoBot:
The MesoBot was being prepped for either additional test dives or the real thing. When it's time to go out to sea it will be loaded into a half-sized shipping container. The other half of the shipping container holds the control room, from which the MesoBot is driven, and a whole bunch of spare parts. When you're two-weeks out to sea and need to replace something, you can't just nip into the nearest Home Depot. Besides, many of the parts that make up these robots are special-built of materials like titanium and can be built only by MBARI engineers.
When it's time to head out to sea, both shipping containers are loaded by crane onto the deck of the research ship. Then off they go!
This is another robot. Nice to see that amidst all this high-tech stuff, they still use ordinary Kim-Wipes at MBARI. Now that's a technology I understand!
Unlike ROVs, which are tethered to a ship and operated remotely by technicians on the ship, autonomous underwater vehicles (AUVs) are programmed before they are deployed. At sea, they roam around according to their program. They may be collecting data for mapping the seafloor, measuring water parameters, or detecting and following a phytoplankton bloom. Kim tells a story of an AUV working off the coast of Oregon, I think. Its job was to map the sea floor. It got itself stuck inside an old lava tube. Since they can only move forward, it couldn't get out. So it sent up an SOS ping and had to be located and then pulled out of the lava tube by an ROV.
This is the lab where AUVs are built:
Kim always takes us inside to see the big testing pool, and it always feels a little creepy to me. The pool is filled with filtered seawater, and engineers use it to test their devices before sending them out into the ocean.
These grids at the bottom of the pool are used to test a robot's cameras:
MBARI is located in Moss Landing, right in the middle of the backwards letter 'C' that is Monterey Bay. Its location is especially strategic because one arm of the Monterey Canyon begins about 100 yards off the jetty at the Moss Landing harbor. This means that the deep sea is relatively easy to get to from this location. One of MBARI's ships, the R/V Rachel Carson, makes day trips into Monterey Bay. Her ship operators, technicians, and scientists can explore the deep sea and come home every night to sleep in their own beds.
Here's Kim pointing out to where the Monterey Canyon begins:
All in all, for anyone interested in marine science and technology, MBARI is the place to be. And even if you're not a marine scientist or a technophile, you certainly can't complain about the view!
When we stop to marvel at the wonders of the natural world, we usually forget about all the life that is going on that we don't get to see. But there is a lot happening in places we forget to look. For example, any soil is an entire ecosystem, containing a variety of small and tiny animals, bacteria, and fungi. In fact, if a fungus didn't send up a fruiting body (a.k.a. mushroom) every once in a while, most observers wouldn't realize it was there at all. We humans tend to behave as though something unseen is something that doesn't exist, and I admit to the very same thinking with regards to my own kitchen: anything stored way up in cupboards I can't reach, may as well not be there at all.
But there are places where we can witness the life occurring below our feet, and floating docks in marinas and harbors are some of the best. Of course, the trick is to "get your face down where your feet are", a piece of advice about how to observe life in tidepools that applies just as well to investigating the dock biota. Once you get used to the idea of lying on the docks, which can be more or less disgusting depending on time of year and number of birds hanging around, a whole new world literally blossoms before your eyes.
Some of the flower-looking things are indeed anthozoans ('flower animal') such as this plumose anemone:
and this sunburst anemone:
Other animals look like dahlias would look if they were made of feathers. Maybe that doesn't make sense. But see what I mean?
This is Eudistylia polymorpha, the so-called feather duster worm. These worms live in tough, membranous tubes attached to something hard. They extend their pinnate tentacles for feeding and are exquisitely sensitive to both light and mechanical stimuli. There are tiny ocelli (simple, light-sensing eyes) on the tentacles, and even casting a shadow over the worm causes it to pull in its tentacles very quickly. This behavior resembles an old-fashioned feather duster, hence the common name. These were pretty big individuals, with tentacular crowns measuring about 5 cm in diamter. Orange seems to be the most common color at the Santa Cruz harbor.
One of the students pointed down at something that he said looked like calamari rings just below the surface. Ooh, that sounds intriguing!
And he was right! Don't they look like calamari rings? But they aren't. These are the egg ribbons of a nudibranch. They appeared to have been deposited fairly recently, so I went off on a hunt for the likely parents. And a short distance away I caught the nudibranchs engaging in the behavior that results in these egg masses. Ahem. I don't know if the term 'orgy' applies when there are three individuals involved, but that's what we saw.
To give you some idea of how these animals are oriented, that flower-like apparatus is the branchial (gill) plume, which is located about 2/3 of the way down the animal's dorsum. The anterior end bears a pair of sensory organs called rhinophores; they look kind of like rabbit ears. You can see them best in the animal on the left.
When you see more than one nudibranch in such immediate proximity it's pretty safe to assume that they were mating or will soon be mating. Nudibranchs, like all opisthobranch molluscs, are simultaneous hermaphrodites, meaning that each can mate as both a male and a female. The benefit of such an arrangement is that any conspecific individual encountered is a potential mate. The animals pair up and copulate. I'm not sure if the copulations are reciprocal (i.e., the individuals exchange sperm) or not (i.e., one slug acts as male and transfers sperm to the other, which acts as female). In either case, the slugs separate after mating and lay egg masses on pretty much whatever surface is convenient. Each nudibranch species lays eggs of a particular morphology in a particular pattern. Some, such as P. atra, lay eggs in ribbons; others produce egg masses that look like strings of miniature sausages.
This is the first time I've seen big Polycera like these. The slugs were about 4 cm long. They eat a bryozoan called Bugula, and there is a lot of Bugula growing at the harbor these days. Maybe that's why there were so many Polycera yesterday. Nudibranchs are the rock stars of the invertebrate world--they are flamboyantly and exuberantly colored, have lots of sex, and die young. They can be very abundant, but tend to be patchy. Quite often an egg mass is the only sign that nudibranchs have been present.
The next time you happen to be at a marina poke your head over the edge and take a look at the stuff living on the dock. Even if you don't know what things are, you should see different textures and colors. With any luck, you'll be pleasantly surprised at the variety of life you find under your feet.
This time of year is when California earns its nickname as the Golden State. It isn't only the dried vegetation blanketing the hillsides. The light itself takes on a golden hue, especially in the morning and evening when the sun is low on the horizon. Photographers call the time periods just after sunrise and just before sunset the 'golden hour' and with good reason. Some of my favorite photos were taken in either the early morning or late evening.
Today the Elkhorn Slough National Estuarine Research Reserve (ESNERR) held an open house event. Booths were set up on the field outside the visitor center, with information on native plants, research projects taking place at the slough, a watershed demonstration, mosquito abatement tactics, face painting for kids, and even a food truck. I hadn't been to the slough since early summer, and when I got the notice about the open house I decided to spend the morning there. I'd hike around a bit, take some pictures, and do some nature journaling.
It certainly was a beautiful morning. It had been swelteringly hot earlier in the week, and fortunately the heat had lessened. There was a strong cool breeze and the sky was a clear blue.
In the spring, when I bring my Ecology students to the slough, the landscape is green. The grasses are green and wildflowers are in bloom. Even the pickleweed looks nice and fresh in the spring. Six months later, however, those same grasses are brittle and brown, and most of the wildflowers have long gone to seed and senesced. The live oaks retain their foliage throughout the year, and after two successive wet winters they are lush and green.
When I arrived at the reserve this morning I spent a few minutes touching base with acquaintances and meeting some new people, then wandered off on one of the trails. It was a little chilly, very welcome after the previous heatwaves, and I sat on a bench to do some painting and looking around. After about half an hour I heard something behind me that didn't sound like the wind blowing through the grasses. It was much more rhythmic and regular--definitely some critter walking through the brush. Very quietly, I stood up and sneaked around the oak tree to see a group of three or four juvenile wild turkeys disappearing into a thicket.
All in all I had a pretty good two hours of bird watching. I don't consider myself a birder, really. I enjoy watching birds, just like I enjoy watching other animals. The competitive aspect of birding is a real turn-off for me. I don't care about keeping a life list and comparing it to anybody else's. That said, I do like to keep note of what I see at a given time and place, because it helps me understand the natural world a little better. For example, the other day I heard my first golden-crowned sparrow of the season, and although I haven't seen it yet, knowing it is there makes me think that autumn has truly arrived.
In past decades, several different groups of people have been working to restore natural habitat to the slough. One of the earlier ideas was to build artificial islands, hoping they would encourage the marsh plants such as pickleweed to recruit and expand to their former abundance. It didn't really work, but the islands do provide places for resident and migratory birds to stop and rest.
More recently, a consortium of stakeholders has worked to restore marshlands closer to the ocean. They filled in areas that had been completely flooded, and pickleweed recruited there on its own. That area has been restored to a much more natural condition, with meandering waterways and pickleweed that isn't drowned by seawater. Elkhorn Slough falls into several jurisdictions at the federal, state, and local levels, and getting these groups to work together for a common goal can be difficult. The success that they have had speaks to their willingness to cooperate. I think it helps that any actions taken are based on science, rather than politics or economics.
Over the summer, a lot of work was done to eradicate non-native plant species. This work is ongoing, and may very well never be finished, but it is good to the ecosystem to try. An island called Hummingbird Island has been rid of invasive eucalyptus trees, and now the only trees there are native live oaks and cypress. The trail I hiked went through several areas where trees has been cut down.
Remember that train I mentioned? Here it is, traveling through the slough at about midday.
Sometimes visitors to the slough don't believe that those tracks are actually used.
Much of the land that the ESNERR sits on used to be a dairy. These barns are, I think, the only dairy buildings that remain. Visitors aren't allowed into Little Barn, but we can walk through Big Barn. It is used for occasional equipment storage and is inhabited by barn owls. Sometimes we find owl pellets on the ground beneath the owl boxes mounted in the barn. It is also not unusual to find pieces of those old-fashioned glass milk bottles near the trails.
When I was a little kid I disliked autumn because the shortening days meant that summer was over and winter was coming. As I grow older, though, and gain a presumably more mature outlook on life, I am more able to appreciate the glory of autumn. I still think spring is my favorite season of the year, but autumn in California is indeed golden and lovely.
We usually think of sea stars as the colorful animals that stick to rocks in the intertidal. You know, animals like Pisaster ochraceus (ochre star) and Patiria miniata (bat star). I see these animals all the time in the intertidal, and if you're a regular reader of this blog you've probably seen the photos that I post here. Given how prominent P. ochraceus and P. miniata can be in the rocky intertidal, it may be a bit of a surprise to learn that not all sea stars live on rocks. In fact, some can't even really stick to a rock.
This morning I was meandering through the Seymour Center when I stopped at a recently refurbished tank. The new inhabitants are a couple of curlfin sole (Pleuronichthyes decurrens) and their secretive and strange roommate. Here's one of the flat fish:
The other fish was hiding up against the wall in one of the back corners and didn't come down until it was feeding time.
The secretive roommate was all but invisible. Here's a photo. Ignore the fish's tail. Do you see anybody else?
Fortunately for all of the tank's inhabitants, feeding time was just around the corner. I knew what would happen, so I stuck my phone on the glass and recorded some video. Keep an eye on the upper left-hand corner. Watching the fish eat is entertaining, too. Just how do they manage with those tiny sideways mouths?
It's not the greatest bit of video, but did you see what happened? That creature emerging from the sand is Astropecten armatus, a sea star that lives in sand. And did you notice how fast it moves? Most of the time it is buried under the sand and usually comes out only to grab food. Every once in a while I'll find it on one of the walls but most of the time it is essentially invisible to human viewers on the other side of the glass.
All spread out, this Astropecten is probably a little smaller than my hand. It has a smooth-ish aboral (i.e., top) surface, lacking the spiny protuberances that Pisaster has. The texture of the aboral surface is similar to that of the bat star, Patiria miniata. The species epithet, armatus, means 'armored' and refers to the row of marginal plates along the perimeter of the body. These plates bear a row of spines that point up and another row that point down. Astropecten is unusual among sea stars for having suckerless tube feet. Its tube feet are pointed, and instead of being super grippy, work to push sand around so the animal can sort of bulldoze its way along. As always, form follows function!
In the wild, A. armatus lives on sandy flats, rarely exposed even at low tide. One of its favorite prey items is the olive snail, Olivella biplicata. Imagine this life-and-death encounter taking place below the surface of the sand: Olivella is burrowing through the sand, minding its own business and unaware that Astropecten is following the slime trail it (Olivella) left behind. Astropecten catches up to Olivella, shoves a couple of arms into the sand around Olivella, engulfs the snail, and swallows it whole. Eventually an empty Olivella shell is spat out. Incidentally, many small hermit crabs, especially Pagurus hirsutiusculus and juveniles of other Pagurus species, live in Olivella shells. I've often wondered why there are so many empty but intact olive snail shells for the hermit crabs to find, and now suppose that Astropecten's method of feeding might have something to do with it.
Interesting star, this Astropecten. I'm really happy that it is on exhibit again, because even most visitors will never see it, watching it come out to feed is always fun.