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All semester I've been taking my Ecology students out in the field every Friday. We've visited rivers, forests, natural reserves, endemic habitats, and fish hatcheries--none of which fall into my area of expertise. This year I have several students interested in various aspects of food production, natural/holistic health practices (which sometimes conflict with actual science!), mycology, as well as some who haven't yet decided in which direction to take their academic endeavors. Until very recently I haven't been able to share with my students much of what I really know, which is marine biology. I did have them learn the organisms that live on docks at the harbor, but that was to study the process of ecological succession rather than natural history.

Yesterday, finally, I took the class into my real field, the rocky intertidal. This year it happened that the best Friday to do our annual LiMPETS monitoring was at the end of the semester. We welcomed the new regional LiMPETS coordinator, Hannah, to our classroom on Thursday for some training. Students learned about the history of the LiMPETS program, some natural history of the rocky intertidal in California, and got to practice some organism IDs with photo quadrats of actual intertidal areas.

The real fun, of course, occurs in the field where the organisms live. So we went here:

LiMPETS monitoring at Davenport Landing
2019-05-10
© Allison J. Gong
Sampling along the vertical transect
2019-05-10
© Allison J. Gong

We didn't have a very good student turnout, unfortunately, but the ones who did show up were diligent workers and we got everything finished that Hannah needed. Most of the time was spent sampling along the permanent vertical transect line. This line is sampled at 3-meter increments along a line that runs from the high intertidal into the low. The same quadrats are sampled every time, and the data collected are used to determine how specific sites change over time. The most difficult part of the monitoring is finding the eye bolts that mark where the transects begin!

Sampling along the vertical transect
2019-05-10
© Allison J. Gong

I admit, I was a little bummed at the low turnout and late arrival of my students. But the intertidal is the intertidal, and it didn't take long for me to adjust my attitude. I worked up a handful of quadrats with Hannah, then let the students do the bulk of the heavy lifting. This was their field trip, after all. So I wandered around a bit, remaining within hearing distance in case I was needed. I needed to find some stuff!

I just want to show some of the animals and algae in the intertidal yesterday. I didn't realize how much I missed this basic natural history stuff until I got to spend some time simply looking at things.

Such rich life to see! One of the students was astounded when she learned that we could visit sites like this only a few days each month. "At dinnertime today the spot where you're standing will be under several feet of water!" I told her. Mind blown.

Intertidal biota at Davenport Landing
2019-05-10
© Allison J. Gong

Looking more closely, there were, as usual, interesting zonation patterns to observe. One was the restriction of large brown algae to the vertical faces of rocky outcroppings.

The kelp Laminaria setchellii at Davenport Landing
2019-05-10
© Allison J. Gong

In the mid-intertidal, mussels (Mytilus californianus) rule the roost. They are often (but not always) accompanied by gooseneck barnacles (Pollicipes polymerus). The barnacles, for reasons discussed in this earlier post, always live in clumps and are most abundant in the lower half of the mid-intertidal mussel beds.

Gooseneck barnacles (Pollicipes polymerus) and mussels (Mytilus californianus) at Davenport Landing
2019-05-10
© Allison J. Gong

During the training session on Thursday, Hannah told the students that Pollicipes is easily identifiable because the barnacles look like dragon toes. I think I can sort of see that. They are scaly and strange enough to be dragon toes.

Gooseneck barnacles (Pollicipes polymerus) at Davenport Landing
2019-05-10
© Allison J. Gong

The algae are taking off now, and the site is starting to look very lush.

Mishmash of algae at Davenport Landing
2019-05-10
© Allison J. Gong

Even algae start as babies! These balloon-shaped things are young Halosaccion glandiforme thalli, surrounded by other red algae. The large blades belong to Mazzaella flaccida, which makes up a large portion of algal biomass in the mid-intertidal zone.

Halosaccion glandiforme and Mazzaella flaccida at Davenport Landing
2019-05-10
© Allison J. Gong

The tidepools at Davenport Landing are good places to see fish, if you have the patience to sit still for a while and watch. This woolly sculpin (Clinocottus analis) posed nicely in the perfect pool for photography--deep enough to submerge the camera, with clear, still water.

Woolly sculpin (Clinocottus analis) and purple urchins (Strongylocentrotus purpuratus) at Davenport Landing
2019-05-10
© Allison J. Gong

And I was finally able to take a good underwater shot of a turban snail carrying some slipper shells. I've already written about the story of this gastropod trio in case you need a refresher. I'm still waiting to see a taller stack of slipper shells some day.

Black turban snail (Tegula funebralis) with slipper shells (Crepidula adunca) at Davenport Landing
2019-05-10
© Allison J. Gong

It was impossible not to feel satisfied after spending some time looking at these creatures. My attitude was mercifully adjusted, and we all departed feeling that we'd done a good morning's work. Our small group of students was able to collect a full set of data for Hannah. That ended up being a very important accomplishment, as Hannah doesn't have any other groups monitoring at Davenport this spring. This means that our data will probably be the only data collected this year at this site. I'm glad the tide and weather conditions allowed us to stay out there as long as we did.

1

For a number of reasons--a lingering injury to my bum knee, scheduling difficulties, and ongoing postconcussion syndrome--I missed the autumn return of the minus tides. At this time of year the lowest tides are in the afternoon, and at the end of the day I just didn't have the energy to deal with field work. It took until today, the winter solstice, for me to find my way back to the intertidal. An additional motivating factor was a request from both the Seymour Center and Seacliff State Beach for critters to populate their displays. So off I went!

Davenport Landing beach
Davenport Landing Beach
21 December 2018
© Allison J. Gong

Over the past day or so a storm system blew through the area. It didn't drop any rain on us in Santa Cruz, but earlier this week the National Weather service issued a small craft advisory and suggested that people stay off the beach, due to a combination of big swell and high tides. Usually when I go collecting at Davenport I go to the reef on the north end of the beach, which has more varied vertical topography and a similar, but generally richer, biota than the gently sloping benches to the south. However, the big swell had washed away a lot of the sand, leaving the beach steeper than it would be in the summer, and even the -1.0 ft tide didn't make the reef safely available to someone not clad in a wet suit.

So I trudged across the beach and went to the south instead. It gave me an excuse to poke at the stuff that had been washed up onto the beach and look for nice pieces of algae to take to the Seymour Center. Algal pickings are rather slim in the winter, but I did find several decent small clumps that will do nicely in the touch table. One noteworthy find was a dead gumboot chiton (Cryptochiton stelleri). There were four such corpses washed up on the beach, in varying states of decay and stench.

Cryptochiton stelleri
Dead gumboot chiton (Cryptochiton stelleri)
21 December 2018
© Allison J. Gong

Cryptochiton stelleri is the largest of the chitons, routinely growing to length of 20 cm. It's a hefty beast, too. The chitons as a group have their greatest diversity in the intertidal, but Cryptochiton is a subtidal creature. Unlike the intertidal residents, Cryptochiton's sticking power is pretty weak. Living below the worst of the pounding of the waves, it generally doesn't have to cling tightly to rocks. However, because it doesn't stick very well, Cryptochiton often gets dislodged by strong surge, especially during spring tides. Then they get tumbled by the waves and wash up dead on the beach. I don't think I've ever seen a live Cryptochiton washed up.

The reef to the south of the beach consists of flat benches that slope down to the ocean. There are some channels and a few pools, but otherwise there is no real topography. Of course, for creatures living in the intertidal, there is topography--the nooks and crannies, as well as vertical faces, provide a variety of microhabitats.

Intertidal benches on the south end of Davenport Landing
21 December 2018
© Allison J. Gong

Mopalia lignosa is one of the intertidal chitons that I'm always delighted to find because it's not as common as some of the others, and it's a beautiful animal. The species epithet lignosa means 'wood' and refers to the patterning on the dorsal shell plates.

Mopalia lignosa
21 December 2018
© Allison J. Gong

As usual, there were spectacular anemones to be seen. And I saw something new! Anthopleura sola, the sunburst anemone, is one of the large aclonal anemones that is very common. At Natural Bridges there is a brilliant fluorescent A. sola in a pool on one of the benches I visit. I've been keeping an eye on this animal for a couple of years now, just to reassure myself that it's still there and doing well. The animal is hardly hidden, but it feels like a little insiders' secret that not everybody knows about.

For the first time, I saw fluorescent A. sola at Davenport Landing. Three of them, in fact! And boy, were they all bright!

Fluorescent Anthopleura sola anemone
21 December 2018
© Allison J. Gong
Another fluorescent Anthopleura sola anemone
21 February 2018
© Allison J. Gong

The third fluorescent anemone was closed up. There were just enough partial tentacles visible to see that it is indeed a fluorescent specimen.

A third fluorescent Anthopleura sola anemone
21 December 2018
© Allison J. Gong

Now, I don't spend as much time at the south end of the beach as I do on the north side, but until today I had never noticed these fluorescent animals. Could I have missed them all this time? It's kind of hard to miss a neon green animal the size of a cereal bowl! At any rate, now that I know they exist and hopefully remember where they are, I'll be able to keep an eye on them, too.

When low tides occur at or before dawn, a marine biologist working the intertidal is hungry for lunch at the time that most people are getting up for breakfast. And there's nothing like spending a few morning hours in the intertidal to work up an appetite. At least that's how it is for me. Afternoon low tides don't seem to have the same effect on me, for reasons I can't explain. A hearty breakfast after a good low tide is a fantastic way to start the day.

Sea anemones are members of the Anthozoa (Gk: 'antho' = 'flower' and 'zoa' = 'animal'). These 'flower animals' are the largest cnidarian polyps and are found throughout the world's oceans. They are benthic and sedentary but technically not sessile, as they can and do walk around, and some can even detach entirely and swim away from predators. The anthozoans lack the sexual medusa stage of the typical cnidarian life cycle, so the polyps eventually grow up and have sex. In addition to the sea anemones, the Anthozoa also includes the corals, sea pens, and gorgonians.

With their radial symmetry and rings of petal-like tentacles, the sea anemones do indeed resemble flowers. You've seen many of my anemone photos already. Here's one more to drive home the message.

Anthopleura artemisia at Pistachio Beach
27 January 2017
© Allison J. Gong

Sea anemones are cnidarians, and cnidarians are carnivores. Most of the time  anemones in the genus Anthopleura feed on tiny critters that blunder into their stinging tentacles, although the occasional specimen will luck into a much more substantial meal. I've watched hermit crabs crawl right across the tentacles of a large anemone (Anthopleura xanthogrammica), and while the anemones did react by retracting the tentacles, the crabs easily escaped their grasp.

Of course, not all potential prey items are so fortunate. Sometimes even big crabs get captured and eaten, like this poor kelp crab (Pugettia producta):

Kelp crab (Pugettia producta) being eaten by an anemone (Anthopleura sp.) at Davenport Landing
8 March 2017
© Allison J. Gong

There's no way to know exactly how this situation came to be. Was the crab already injured or weakened when the anemone grabbed it? Or was the anemone able to attack and subdue a healthy crab? I've always assumed that the exoskeleton of a crab this size would be too thick for the rather wimpy nematocysts of an Anthopleura anemone to penetrate, but maybe I'm wrong. A newly molted crab would be vulnerable, of course; however, they tend to stay hidden until the new exoskeleton has hardened, and the crab in the above photo doesn't appear to have molted recently.

Even big, aggressive crabs can fall prey to the flower animals in the tidepools. I'd really like to have been there to watch how this anemone captured a rock crab!

Giant green anemone (Anthopleura xanthogrammica) eating a rock crab, possibly (Romaleon antennarium) at Natural Bridges
17 June 2018
© Allison J. Gong

And crabs aren't the only large animals to be eaten by sea anemones. Surprisingly, mussels often either fall or get washed into anemones, which can close around them. Once a mussel has been engulfed by an anemone, the two play a waiting game. Here's what I imagine goes on inside the mussel: The bivalve clamps its shells shut, hoping to be spit back out eventually; meanwhile, the anemone begins trying to digest the mussel from the outside; sooner or later the mussel will have to open its shells in order to breathe, and at that point the anemone's digestive juices seep inside and do their work on the mussel's soft tissues. When the digestive process is finished, the anemone spits out the perfectly cleaned mussel shells.

Giant green anemone (Anthopleura xanthogrammica) digesting a clump of mussels (Mytilus californianus) at Natural Bridges
17 June 2018
© Allison J. Gong

In the photo above, the anemone is working on a clump of several mussels. I can't see that any of these mussels have been compromised, but the pale orange stringy stuff looks like mussel innards and slime. It could be that several mussels are still engulfed within the anemone. There is always a chance that an anemone will give up on a mussel that remains tenaciously closed, and spit it out covered with slime but otherwise unharmed. I assume that hungry anemones are less likely to give up their meals than ones that have recently fed.

So how, exactly, does an anemone eat a mussel, or a crab? The answer lies within the anemone's body. Technically, the gut of an animal is outside its body, right? Don't believe me? Let's think it through. An animal with a one-way gut can be modeled as a tube within a tube, and by that reasoning the surface of a gut is contiguous with the outer surface of the body. Our gut is elaborated by pouches and sacs of various sizes and functions, but is essentially a long, convoluted tube with a mouth on one end and an anus on the other. Sea anemones, as all cnidarians, have a two-way gut called a coelenteron or gastrovascular cavity (GVC), with a single opening serving as both mouth and anus. Anemones, being the largest cnidarian polyps, have the most anatomically complex gut systems in the phylum.

Imagine a straight-sided vase with a drawstring top. The volume of the vase that you'd fill with water and flowers represents the volume of the anemone's gut. Anemones can close off the opening to their digestive system by tightening sphincter muscles that surround the mouth; these muscles are analogous to the drawstring closure of our hypothetical vase. Now imagine that the inner wall of the vase is elaborated into sheets of curtain-like tissue that extend towards the center of the cavity. These sheets of tissue are called mesenteries. They are loaded with various types of cnidocytes that immobilize prey and begin the process of digestion. The mesenteries greatly increase the surface area of tissue that can be used for digestion. The mesenteries are also flexible and can wrap around ingested prey to speed things up.

This anemone (below) that was eating both a mussel and a piece of kelp:

Sunburst anemone (Anthopleura sola) having brunch at Davenport Landing
4 May 2018
© Allison J. Gong

Those frilly ruffles are the mesenteries. You can see how greatly they'd increase the surface area of the gut for digestion. They are also very soft, almost flimsy. Here's a close-up shot:

Gastric mesenteries of the sea anemone Anthopleura sola at Davenport Landing
4 May 2018
© Allison J. Gong

Maybe I'm especially suggestible, but seeing these animals working on their own meals makes me hungry, too. After crawling around the tidepools for a few hours I'm always ready for a second breakfast or brunch of my own.

Bon appétit!

This week I celebrate the return of the early morning low tides! I was very much looking forward to this tide series, and even though I am in class on Tuesday, Thursday, and Friday mornings I wanted to go out on as many of the tides as possible. On Wednesday morning I went out to Natural Bridges to meet up with one of my students, Maddie, who is studying anemones for her independent research project. The tide wasn't particularly early at 07:08, but there was nobody out there. No surfers, even. The only person I saw out there was Maddie.

There are few things better than an overcast morning in the intertidal. Peaceful, calm, not windy, and uncrowded. I could feel the stress melting away as the only sounds I heard were the coming and going of the surf and the high-pitched 'cheeps' of the oystercatchers.

18 April 2018
© Allison J. Gong

Natural Bridges is probably the intertidal site that I know the best. It's close to home, so access is easy. It is a state park and a marine protected area, so collecting of any sort is not allowed and the tidepools are about as undisturbed as can be, considering that it is heavily visited. And in the early morning the intertidal is just wonderful. Visiting there and having time to slow down and really pay attention is a real treat for me.

And perhaps the homecoming I felt this morning is due to the fact that just last week I gave a talk to the docents at Natural Bridges State Park. There's something about this particular group that inspires me and rekindles my interest in this special site.

It is now springtime, and the intertidal is in the full flush of reproduction. The algae are starting to regrow and hinting of the lush coverage that we'll see in the next few months.

Ulva sp. at Natural Bridges
18 April 2018
© Allison J. Gong

There are several species in the genus Ulva, referred to as the sea lettuces. They come in a variety of morphs, but all are variations on the same theme: a thin sheet, two cell layers thick. Some Ulva species have blades that are large, while in other species the sheets are rolled into thin tubes or short tufts. Many of them look alike, making field ID problematic, so with few exceptions I simply call them all Ulva sp.

The other common green alga at Natural Bridges is one of the filamentous green, Cladophora columbiana. It has a short thallus, rising from the rock surface like a stout pincushion, which is what it feels like. It grows in little clumps among the mussels in the mid-intertidal.

The green alga Cladophora columbiana and little periwinkle snails, Littorina sp., at Natural Bridges
18 April 2018
© Allison J. Gong

Today I saw Cladophora with little periwinkle snails, an association that, in my experience, is unusual. The periwinkles are small, less than 10 mm from aperture to apex, and I tend to think of them as a high intertidal species. Cladophora can also occur in the high-mid intertidal but for some reason seeing them together with the periwinkles took me by surprise. There were many of the little snails crawling around in the mid zone, on bare rock or on other animals.

In fact, today was a good day to see lots of animal recruitment. Several areas of rock in the mid-intertidal that were recently devoid of animal life have been colonized by mussels or acorn barnacles.

Small acorn barnacles at Natural Bridges.
18 April 2018
© Allison J. Gong

Most of the individuals in this field of barnacles are Chthamalus dalli/fissus. Those are the small, light brown barnacles. The taller whitish barnacle near the center of the photo is Balanus glandula. But see all the teensy barnacles below and slightly to the left of the Balanus? Those are new recruits, 1-2 mm in diameter. If you click on the photo for a larger view, you can see that while most of the recruits are Chthamalus, there are a few Balanus in there as well. And notice that some of the recruits have landed on other barnacles. This is a smart decision for them. As I've described before, barnacles can't reproduce unless they have close neighbors of the same species. Settling on an established conspecific adult is one way to guarantee that a young barnacle will have potential mates when it grows up.

The largest barnacle in the intertidal around here is the pink barnacle, Tetraclita rubescens. It is fairly common at Natural Bridges, and quite conspicuous because of its size and pink color.

A pink barnacle, Tetraclita rubescens, encrusted with Balanus glandula and Chthamalus fissus/dalli at Natural Bridges
18 April 2018
© Allison J. Gong

And take a look at this owl limpet! She's carrying a whole world on her back.

An owl limpet (Lottia gigantea) encrusted with barnacles, at Natural Bridges
18 April 2018
© Allison J. Gong

Speaking of owl limpets, their tendency to monopolize territories in the intertidal can strongly affect the makeup of the community. It's not just the barnacles that recruit to the intertidal in the spring; mussels do the same, and often quite spectacularly. The disappearance of predatory ochre stars (Pisaster ochraceus) due to sea star wasting syndrome (SSWS) allowed mussels to expand lower into the intertidal, where they would ordinarily be eaten. The ochre stars have been reappearing in the past few years, and hand-sized P. ochraceus are now very common at Natural Bridges. We would now expect predation to cause the lower edge of the mussel bed to retreat back up a bit.

Mussels cannot recruit to Lottia farms because the limpets routinely cruise around their territories and scrape off any newly settled larvae. Lottia farms occur in what would otherwise be prime real estate for mussels, except for the fact that the larvae landing there never get a chance to become established. However, even a big owl limpet doesn't live forever, and when one dies a whole swath of now-vacant area becomes available.

Mussel bed with recent recruits at Natural Bridges
18 April 2018
© Allison J. Gong

Those two bare patches in the photo above are former Lottia farms. I looked for the owl limpets and didn't find them. And note that band of young mussels running horizontally in the middle of the photo. They are young mussels, relatively clean of encrusting mussels or algae, but aren't new recruits. I'd guess that they've been there a few months. Whatever the age of the mussels, they are taking advantage of the space that used to be occupied and defended by an owl limpet. Or maybe two owl limpets, as that space would be a very large farm for a single limpet.

After two days of class taking me out of the intertidal, I get to spend the next two mornings back out there. I have some collecting to do!

2

Who do you think makes these tracks in the sand?

15 February 2018
© Allison J. Gong

Any guesses?

Here's another photo, taken from farther away to give you a bigger picture of the scale of things.

15 February 2018
© Allison J. Gong

Believe it or not, the maker of these trails is the little black turban snail, Tegula funebralis. They are one of my favorite animals in the intertidal, for a number of reasons:

  1. I always root for the underdog and the under-appreciated, and these snails are so numerous in the intertidal that they are practically invisible. People literally do not see them. I know, because I ask.
  2. They are very useful creatures to keep as lab pets. I throw a few of them into each of my seawater tables, except for the table that contains a resident free-ranging sea star, and they do a fantastic job keeping algal growth to a tolerable minimum. They're my little marine lawnmowers!
  3. They come in very handy when I'm teaching invertebrate zoology. Students study them live to observe behavior, and the snails are not shy. They are very tolerant of being picked up and gently prodded, and soon emerge from their shells and carry on their little snail lives. Students also dissect them in lab to learn about gastropod anatomy.

So yes, these tracks in the sand are made by T. funebralis in the high intertidal. In areas where a layer of sand accumulates either at the bottom of a pool or on a flat exposed rock, it is not uncommon to see a turban snail pushing sand out of the way as it crawls along, like a miniature snow plow.

A black turban snail (Tegula funebralis) plowing through sand on a high intertidal rock at Natural Bridges
15 February 2018
© Allison J. Gong

Tegula funebralis and its congeners are called turban snails because their shells are shaped like turbans. Given their small size (a big T. funebralis would have a shell height of 2.5-3 cm), pushing sand around must be a tiresome chore. They do it because they have no choice. Most grazing gastropods, such as turban snails and limpets, can feed only when they are crawling. There may very well be a nice yummy layer of algal scum on the surface of this rock, but the snail has to push the sand out of the way before it can feed on it.

Here's another photo, taken at the snail's level.

Tegula funebralis plowing through sand at Natural Bridges
15 February 2018
© Allison J. Gong

This snail is pushing through a wall of sand as tall as itself! I don't know about you, but I sure as heck couldn't do that. Props to these little snails!

 

2

Although the world's oceans cover approximately 70% of the Earth's surface, most humans interact with only the narrow strip that runs up onto the land. This bit of real estate experiences terrestrial conditions on a once- or twice-daily basis. None of these abiotic factors, including drying air, the heat of the sun, and UV radiation, greatly affects any but the uppermost few meters of the ocean's surface so most marine organisms don't need to worry about them. Despite the apparent paradox of where they live, intertidal organisms are also entirely marine--they cannot survive prolonged exposure to in air or freshwater. So how do they manage to live here?

Some organisms have a physiological tolerance for difficult conditions. These tidepool copepods and periwinkle snails, for example, are able to survive in the highest pools in the splash zone, where salinity can be either very high (due to evaporation) or very low (due to rain or freshwater runoff), dissolved oxygen is often depleted due to high temperature, and temperature itself can be quite warm. Sculpins and other tidepool fishes cope with low oxygen levels by gulping air and/or retreating to deep corners of their home pools.

Of course, animals that can locomote have the option of moving to a more favorable location. Other creatures, living permanently attached to their chosen site, aren't quite so lucky. Let's take barnacles as an example.

Nauplius larva of the barnacle Elminius modestus
© Wikimedia Commons

Barnacles have two planktonic larval stages: the nauplius and the cyprid. The nauplius is the first larval stage and hatches out of the egg with three pairs of appendages. It can be distinguished from the nauplius of other crustaceans by the presence of two lateral "horns" on the anterior edge of the carapace. The nauplius's job is to feed and accumulate energy reserves. It swims around in the plankton for several days or perhaps a couple of weeks, getting blown about by the currents and feeding on phytoplankton.

Cyprid larva of a barnacle

After sufficient time feeding in the plankton, a barnacle nauplius metamorphoses into the second larval stage, the cyprid. A cyprid is a bivalved creature, with the body enclosed between a pair of transparent shells. It has more appendages than the nauplius, and these are more differentiated. If the nauplius has done its  job well, then the cyprid also contains a number of oil droplets under its shell. These droplets are of crucial importance, because the cyprid itself does not feed. For as long as it remains in the plankton it survives on the calories stored in those droplets. The cyprid's job is to return to the shore and find a suitable place on which to settle. Somehow, a creature about 1 mm long, being tossed about by waves crashing onto rocks, has to find a place to live and then stick to it.

Returning to the topic of the challenges that marine organisms face when they live under terrestrial conditions, let's see how these barnacles manage. Along the northern California coast we have a handful of barnacle species living in the intertidal. In the higher mid-tidal regions at some sites, small acorn barnacles of the genera Balanus and Chthamalus may be the most abundant animals.

Mixed population of the acorn barnacles Balanus glandula and Chthamalus dalli/fissus at Davenport Landing
27 June 2017
© Allison J. Gong

However, nowhere is a particular pattern of barnacle distribution more evident than at Natural Bridges. Here, the barnacles in the high-mid intertidal are small, and concentrated in little fissures and cracks in the rock.

I think most of these small (~5 mm) barnacles are Balanus glandula:

Small acorn barnacles (Balanus glandula) at Natural Bridges
11 October 2017
© Allison J. Gong

And here's a closer look:

Small acorn barnacles (Balanus glandula) at Natural Bridges
11 October 2017
© Allison J. Gong

If all of the rock surfaces were equally suitable habitat, the barnacles would be distributed more randomly over the entire area. Instead, they are clearly segregated to the cracks in the rock. Each of these barnacles metamorphosed from a cyprid into a juvenile exactly where it is currently located. The cyprid may be able to move around to fine-tune its final location, but once the decision has been made that X marks the spot and the cyprid has glued its anterior to the rock, the commitment is real and lifelong. The barnacle will live its entire life in that spot and eventually die there. It is quite probable that cyprids landed in those empty areas on the rock, but they didn't survive to adulthood.

How did this distribution of adult barnacles come to be?

There is one very important biological reason for barnacles to live in close groups, and that is reproduction. They are obligate copulators, which I touched on in this post, and as such need to live in close proximity to potential mates. But today I'm thinking more about abiotic factors. In a habitat like the mid-mid rocky intertidal, desiccation is a real and daily threat. Even a minute crack or shallow depression will hold water a bit longer than an exposed flat surface, giving the creatures living there a tiny advantage in the struggle for survival. No doubt cyprid larvae can and do settle on those empty areas of the rock. However, they likely die from desiccation when the tide recedes, leaving only the cyprids that landed in one of the low areas to survive and metamorphose successfully. There are other factors as well, such as the presence of adult individuals, that make a location preferable for a home-hunting cyprid. In addition to facilitating copulation, hanging out in a cluster slows down the rate of water evaporation, giving another teensy edge to animals living at the upper limit of their thermal tolerance.

Lower in the intertidal, where terrestrial conditions are mitigated by more time immersed, barnacles and other organisms do indeed live on flat rock spaces. But at the high-mid tide level and above, macroscopic life exists mostly in areas that hang onto water the longest. Pools are refuges, of course, but so are the tiniest cracks that most of us overlook. Next time you venture into the intertidal, take time on your way down to stop and salute the barnacles for their tenacity.

The intertidal portion of my participation in Snapshot Cal Coast 2017 is complete. I organized four Bioblitzes, two of which consisted of myself and Brenna and the other two for docents of the Seymour Marine Discovery Center (Tuesday) and the docents of Año Nuevo and Pigeon Point State Parks (Wednesday). The four consecutive days of early morning low tides have been exhausting for a concussed brain and a body dealing with bronchitis for the past several weeks. Good thing the low tide arrives 40-50 minutes later, or I'd probably be dead by now. And even so, I tried to take advantage of the later tides to venture a bit farther afield, so I still ended up getting up at the butt-crack of dawn.

But oh, so totally worth it!

Day 3: Davenport Landing with docents from the Seymour Marine Discovery Center, Tuesday 27 June 2017, low tide -1.1 ft at 08:03

Davenport Landing Beach is a sandy beach with rock outcrops and a fair amount of vertical terrain to the north, and a series of flat benches (similar to those at Natural Bridges) to the south. To get to the good spots at the north end you have to do some cliff scrambling, unless the tide is low enough that you can walk around the rock, which happens maybe once or twice a year. Because it's easier to get around on the benches to the south, that's where I took my group for the Bioblitz. The difference in topography also results in some differences in biota and distribution/abundance of organisms; overall biodiversity is probably equivalent at both sites, but certain species are more abundant at one site versus the other.

Intrepid citizen scientists at Davenport Landing
27 June 2017
© Allison J. Gong

The morning we went to Davenport was sunny and (almost) warm. This makes for plenty of light for photography, but also lots of glare of the surface of pools and the wet surfaces of organisms themselves. My most successful photos are the ones I took with the camera underwater. Wanting to improve my skills at identifying algae, I concentrated most of my efforts on them while not ignoring my beloved invertebrates.

Encrusting coralline algae on submerged rock
27 June 2017
© Allison J. Gong

Coralline algae are red algae whose cells are impregnated with CaCO3. This gives them a crunch texture that is unusual for algae. Corallines come in two forms, encrusting and upright, and can be one of the most abundant organisms in the high and mid intertidal. There are several species of both encrusting and upright corallines on our coast, and most of the time they aren't identifiable to species by the naked eye. Sometimes I can distinguish between genera for the upright branching species. However, the encrusting species require microscopic examination of cell size, crust thickness, and reproductive structures, none of which can be observed in the field.

Bullwhip kelp, Nereocystis luetkeana, at Davenport Landing.
27 June 2017
© Allison J. Gong

Some algae are so distinctive that a quick glance is all it takes to know exactly who they are. With its tiny holdfast, long elastic stipe, and single large pneumatocyst, bullwhip kelp doesn't look anything like the other kelps in California. Like most kelps, N. luetkeana lives mostly in the very low intertidal or subtidal, where under certain conditions it can be a canopy-forming kelp. About a month ago I noted a big recruitment of baby Nereocystis kelps in the intertidal on the north side of Davenport Landing Beach. I speculated then that they probably wouldn't persist into the summer. I'll have to take a morning soon to go up and check on them. Anyway, on our Tuesday Bioblitz we found this big N. luetkeana growing in the intertidal. The stipe was about 1.5 meters long and the pneumatocyst was a little smaller than my closed fist. Given that this individual recruited to that spot and has persisted for a few months, probably, it has a good chance of continuing to survive into the fall. Winter storms, especially if they're anything like the ones we had this past year, will most likely tear it off, though.

Coralline algae aren't the only pink things in tidepools. There are pink fish!

Sculpin in tidepool at Davenport Landing.
27 June 2017
© Allison J. Gong

Sculpins are notoriously difficult to ID if you don't have the animal in hand to count things like fin rays and spines. Someone on iNaturalist may be able to ID this fish, but I don't think the photo is very helpful.

And, just because they're my favorite photographic subjects in the intertidal, here's a shot of Anthopleura sola:

Anthopleura sola at Davenport Landing
27 June 2017
© Allison J. Gong

As of this writing, 10 participants in this Bioblitz have submitted 204 observations to iNaturalist, with 70 species identified. I know that some people haven't upload their observations yet, and expect more to come in the next couple of weeks. The docents enjoyed themselves, to the extent that two of them accompanied Brenna and me to our fourth Bioblitz at Pigeon Point.


Day 4: Whaler's Cove at Pigeon Point with rangers (and one docent) from Pigeon Point and Año Nuevo state parks, Wednesday 28 June 2017, low tide -0.6 ft at 08:53

Usually when I go to Pigeon Point I go to the north side of the point, either scrambling down the cliff next to the lighthouse or about half a mile north to Pistachio Beach. When the park rangers and I were organizing this Bioblitz they suggested going to Whaler's Cove, as the access is very easy due to a staircase and would be much easier for docents who aren't used to climbing down cliffs. It ended up being a good decision, as there was much to be seen.

Bioblitzes and iNaturalist are all about photographing individual organisms (as much as possible) so that they can be ID'd by experts in particular fields. This is the 'tree' level of observation I mentioned in my previous post. I find that when I'm taking photos with the intent to upload them to iNaturalist the photos themselves tend to be rather boring. The intertidal is such a dynamic and complex habitat that photos of single species tend to lack the visual interest of the real thing. I've learned that one of my favorite things to see is organisms living on other organisms.

See what I mean?

A nicely decorated mossy chiton, Mopalia muscosa, at Pigeon Point.
28 June 2017
© Allison J. Gong

Four of this chiton's eight shell plates are completely covered with encrusting coralline algae. It is also wearing some upright corallines and at least two other red algae, one of which is Mastocarpus papillatus. This photo produced six observations for iNaturalist.

Which is not to say that single-subject photos are always boring. When the subject is as weighty as this gumboot chiton (Cryptochiton stelleri), it deserves its own photo or two.

Cryptochiton stelleri at Pigeon Point
28 June 2017
© Allison J. Gong

Ventral view of Cryptochiton stelleri
28 June 2017
© Allison J. Gong

The largest chiton in the world, Cryptochiton typically lives in the subtidal or the very low intertidal. Unlike other chitons, it doesn't stick very firmly to the substrate. I was able to reach down and pick up this one with very little effort. In the subtidal this lack of suction isn't a handicap, as water movement there is less energetic compared to the intertidal, and Cryptochiton does quite well. But it doesn't really look like a chiton at all, does it? That's because its eight dorsal shell plates are covered by a thick, tough layer of skin called the mantle. In most chiton species the mantle is restricted to the lateral edges of the dorsal surface. The girdle, as it's called, exposes the shell plates to some degree. We don't see Cryptochiton's shell plates, but if you run your finger down the middle of the dorsum you can sort of feel them underneath the mantle.

Okay, now for some more 'forest' pictures.

Intertidal biota at Pigeon Point
28 June 2017
© Allison J. Gong

I love this one. There's a lot going on in this small area. The greenish-brown algae are actually a red alga, Mazzaella flaccida. There are two large clumps of stuff in the photo. The clump on the left, consisting of round lumps, is a clone of the aggregating anemone Anthopleura elegantissima. The other clump is a mass of tubes of the polychaete worm Phragmatopoma californica. These two clumps were formed in very different ways, reflecting the vastly different biology of the animals that made them.

Anthopleura elegantissima is one of four species of Anthopleura anemones we have in California and is the only one to grow by cloning. It does so via longitudinal fission, in which an anemone literally rips itself in half. I wrote about them last year. Note that in this aggregation, all of the anemones are about the same size. That's because they're all clones of each other and share the exact same genetic makeup.

Whereas a clone of A. elegantissima represents a single genotype formed by cloning, clumps of Phragmatopoma arise by gregarious settlement. Each of the tubes in a clump is occupied by a single worm, which recruited to that spot as a larva and settled down to live its life. When it comes time to look for a permanent home, the planktonic larvae of Phragmatopoma are attracted by the scent of adult conspecifics. The larvae settle on the tubes of existing adults and undergo metamorphosis. Each worm builds its tube as it grows, using some kind of miraculous cement that sticks sand grains together, much as a mason stacks bricks to build a wall. One of the remarkable things about this construction is that the cement is secreted by the animal's body and starts out sticky and then hardens, all in seawater. It's a likely candidate for Best Underwater Epoxy around. Interestingly, Phragmatopoma can build its tube only as a growing juvenile. Adult worms that are removed from their tubes do not build new ones, and soon die.

Here's another nice clump of Phragmatopoma:

Intertidal biota at Pigeon Point
28 June 2017
© Allison J. Gong

Whaler's Cove at Pigeon Point
28 June 2017
© Allison J. Gong

See that pile of rocks out there? That's where we were blitzing. Given the not-so-lowness of the tide I didn't know if we would be able to make it out there. We were lucky, though, and were able to spend ~30 minutes out on that little point.

So far, the Pigeon Point Bioblitz has yielded 204 observations for iNaturalist, with three participants (so far!) identifying 77 species. Several of my observations were of red algae that I did not recognize; hopefully an expert will come along to ID those for me. Snapshot Cal Coast 2017 continues through this weekend. My intertidal Bioblitzes are over, but I hope to contribute one last set of observations by collecting and examining plankton on Sunday.

1

This is the second year that the California Academy of Sciences has sponsored Snapshot Cal Coast, a major effort to document and characterize the biodiversity of the California coast. To this end the Academy has organized several Bioblitzes at various sites in northern California, and solicited volunteers to lead their own Blitzes, either as individuals or with groups. A Bioblitz is a citizen science activity in which people take photographs of organisms or traces of organisms (shells, scat, tracks, etc.), then upload their observations into iNaturalist. Experts then identify the organisms in the observations, and the data are publicly available to anyone who wants to use them.

For Snapshot Cal Coast 2017 I have four Bioblitzes planned for the intertidal. Here are some of my observations made in the first two.

Day 1: Natural Bridges, Sunday 25 June 2017, low tide -1.7 ft at 06:27

My friend Brenna joined me on an early low tide at Natural Bridges. The intertidal topography at Natural Bridges consists of a series of gently sloping benches that are riddled with potholes of various sizes and depths. For the purposes of this Bioblitz I decided to confine my observations to the geological structure that I call the peninsula, which sticks out farther into the ocean than the edges of the benches.

Aerial view of intertidal benches at Natural Bridges, with the "peninsula" circled in red.
26 June 2017
© Google Maps

The peninsula is most easily accessible when the tide is at least as low as -1 ft, although large swell can make it entirely unsafe to do so at even very low tides. Fortunately the swell wasn't big enough to keep me from the peninsula yesterday, and I confined most of my observations to this location. I've found that making observations for Bioblitzes requires a different kind of attention and focus than either collecting or observing for more general purposes. In the spectrum of forest-to-trees levels of observation, Bioblitzes are all about individual trees. When left to my own devices I tend to move quite fluidly between forest-level observations (e.g., broadscale ecological patterns) and tree-level observations (e.g., what organism is that?), and confining myself to only tree-level observations was, well, confining. It's undoubtedly a good discipline, but one that I find a little stifling.

Here are some of the "trees" I saw at Natural Bridges.

Anthopleura sola
25 June 2017
© Allison J. Gong

Haliotis cracherodii, the black abalone
25 June 2017
© Allison J. Gong

I've been keeping an eye on this abalone for a couple of years now. It has gotten bigger and in the last year has become heavily encrusted with other animals and algae. Right now it is sporting lots of acorn barnacles (both large and small), at least one tube of Phragmatopoma californica, limpets, encrusting and upright coralline algae, and other red algae.

The red alga Smithora naiadum 
25 June 2017
© Allison J. Gong

Smithora naiadum is a red alga whose thallus consists of small flat blades. It grows only as an epiphyte on seagrasses, in this case the surfgrass Phyllospadix scouleri. Later in the summer many surfgrass leaves will be almost entirely covered with Smithora.

My favorite observation of the morning was this little hermit crab.

Pagurus hirsutiusculus, the so-called hairy hermit crab
25 June 2017
© Allison J. Gong

I love how this hermit is clinging to a piece of giant kelp. It lives in a shell of the olive snail Olivella biplicata, as many of its conspecifics do. These shells get to a bit over 2 cm in length, and their narrow diameter means there isn't much empty space inside. Fortunately, P. hirsutiusculus is one of the smaller hermit crabs and doesn't need much space.

An extreme low tide like yesterday's has two benefits. The most obvious is that more real estate is exposed, thus more area to explore. The second benefit of a really low tide is time. Much of the biodiversity of the intertidal is in the low-mid and low zones; the lower the tide, the longer it takes for the ocean to return and reclaim its property. I was able to spend the better part of two hours out on the peninsula, which doesn't happen every year. Lucky me!


Day 2: Franklin Point, Monday 26 June 2017, low tide -1.5 ft at 07:15

To get to the beach at Franklin Point you have to hike ~10 minutes over the dunes along a maintained trail. The views along the way are often quite spectacular, even when it's foggy. This morning it was unusually clear, and I wished I had brought along my big camera. For example, looking north towards Pigeon Point I saw this:

View towards Pigeon Point from the Franklin Point trail
26 June 2017
© Allison J. Gong

I mean, come on. How much more beautiful can a vista be?

The intertidal at Franklin Point has changed dramatically over the past year. Heavy storms over the 2016-2017 winter removed about two vertical meters of sand from the beach, exposing rocks that had been buried for years. Even today, months after the peak of the storm season, you can see bare rock that has yet to be heavily colonized by living things.

Mostly bare rock at Franklin Point
26 June 2017
© Allison J. Gong

Primary succession is the sequence of species' arrival and eventual replacement in an area that has never hosted life before. These rocks may very well have served as habitat for organisms years ago, but in my memory they had been buried in sand until the recent storms. Their exposure provides an opportunity to observe primary succession in this very dynamic habitat.

The first organisms to arrive and take hold in any newly available habitat are primary producers. Makes sense, as there is no food for heterotrophs yet. In the case of the intertidal the first visible organisms are algae. The algae at Franklin Point have been going like gangbusters all spring and into the summer. Faunal diversity, on the other hand, has been rather low. I spent quite a while looking at and photographing algae, many of which I couldn't identify in the field.

My favorite red alga, Erythrophyllum delesserioides, at Franklin Point
26 June 2017
© Allison J. Gong

A young specimen of Egregia menziesii at Franklin Point
26 June 2017
© Allison J. Gong

Some things were entirely unfamiliar to me. For example, I'd never seen coralline algae encrusting on the tips of another red alga. And yet, here it is:

Coralline algae
26 June 2017
© Allison J. Gong

As I mentioned above, animal life at Franklin Point has been rather depauperate this year. HOWEVER, I did get to let out a few whoops of triumph when I found this:

The staurozoan Haliclystus sp. at Franklin Point
26 June 2017
© Allison J. Gong

These animals, staurozoans, are incredibly difficult to photograph. Not only are they the same color as many of the algae they live with and attach to, but they like areas where the water is constantly moving back and forth. Plus, the pools and channels where I found them were cloudy with Ulva spooge. I took a lot of pictures of backscatter and blurry staurozoans.

Here's another shot:

Haliclystus sp. at Franklin Point
26 June 2017
© Allison J. Gong

Staurozoans are the strangest and by far the coolest cnidarians. Their common name 'stalked jellyfish' harkens back to when they were considered scyphozoans, close kin to moon jellies (Aurelia) and the like. They are now known to be in their own group, the Staurozoa, related to but not part of the Scyphozoa.

I don't really know why I'm so enamored of the staurozoans. Maybe it's because they are rare and poorly understood. I know them only from Franklin Point and one sighting at Carmel Point. The systematics of the staurozoans is in flux; I'm not brave enough to assign a species epithet to this critter, but a colleague who is one of the people working on this group suggests that it is H. sanjuanensis, a species that has not yet been formally described. All of the staurozoans I saw today were this brownish-red color, but in previous years I've also seen them in a brilliant bottle green. Those would probably be easier to see among all the red algae, but with my luck the green ones would all be hanging out with Ulva.

The very last part of the hike to the intertidal is a steep decline down the dune to the beach. Getting down is easy, you just sort of ski down. Getting up is much more of a challenge. Ever try to climb a sand dune? Each step gets you about a quarter of a step above the last one, so it's hard work, especially when the dune is steep. There have been times that I've hiked all the way out to the beach, only to turn around and go back because I didn't think I'd be able to climb back up the dune in my hip boots. And since I have bronchitis right now by the time I got back to the top today it felt as though I had climbed Mt. Everest.

See?

It's steeper than it looks, especially on the way up
26 June 2017
© Allison J. Gong

All told, I added about 150 observations to iNaturalist these first two Bioblitzes. I'm not really into making observations just to make observations, so for me that 150 is a good two days' production. Now I need to rest up for tomorrow's low tide.

 

1

It seems that most years, the Memorial Day weekend brings some of the lowest spring tides of the year, and 2017 certainly fits the bill. I've been out for the past two days, heading out just as the sun is starting to rise, and already I've seen enough to whet my appetite for more. And with plans for the next few days, I'm pleased to say that my dance card is completely full for this tide series. There are a lot of stories building out there!

Gathering (orgy?) of dogwhelks (Acanthinucella punctulata) at Davenport Landing
27 May 2017
© Allison J. Gong

At this time of year everything is growing and reproducing. Many of the larvae I've seen in the plankton have parents that live in the intertidal; makes sense that those parents should be having sex now. Barnacles, for example, copulate when the tide is high. I've seen them go at it in the lab, but never in the field, as they don't mate while emersed. This morning I interrupted a pair of isopods locked in a mating embrace, and they swam off, still coupled together, when I disturbed them. Other animals were much less shy. Lifting up a curtain of Mazzaella to see what was underneath, I spotted a small group of dogwhelks (small, predatory snails). I can't be certain, but suspect they were having an orgy.

A short distance away I found the inevitable result of the dogwhelk orgies.

Acanthinucella punctulata with eggs, Davenport Landing
27 May 2017
© Allison J. Gong

Each of those urn-shaped objects is an egg capsule, containing a few dozen developing embryos. After the snails copulate the mating individuals go their separate ways. The females lay these egg capsules in patches in the mid-intertidal, usually on a vertical surface under the cover of algae to minimize the risk of desiccation.

For many years now, some of my favorite animals have been hydroids. I worked in a hydroid lab as an undergraduate, and this is when I fell in love with the magic of a good dissecting microscope. A whole new world became visible, and I found it easier than I ever imagined to fall under the spell of critters so small they can't be seen with the naked eye. I still do.

The ostrich-plume hydroid Aglaophenia struthionides, at Davenport Landing
27 May 2017
© Allison J. Gong

Hydroid colonies come in a variety of forms, shapes, and colors. Most of them are small and cryptic, resembling plants more than any 'typical' animal, and aren't easily seen unless you're looking for them. One intertidal species, however, is pretty conspicuous even to the casual tidepool visitor or beachcomber. It often gets torn off its mooring and washes up on the beach.

A hydroid colony is the benthic polyp stage of the standard cnidarian life cycle. The polyp represents the clonal phase of the life cycle and reproduces by dividing to make several copies of itself. In a colony such as a hydroid, the polyps remain connected to each other and even share a common digestive system. The polyps don't reproduce sexually. That function is reserved for the medusa stage of the life cycle. Some hydroid colonies produce free-swimming medusae, and others hang onto reduced medusa buds or structures so un-medusa-like that they're called gonangia. Aglaophenia is a hydroid that houses its sexual structures in gonangia that are located on the side-branches of the fronds.

Here's a closer view of a single frond of the Aglaophenia colony. I had to bring it back to the lab to look at it under the scope.

Frond of a colony of Aglaophenia struthionides, showing gonangia
27 May 2017
© Allison J. Gong

The gonangia look like leaves, or pages of a book, don't they? After working a low tide I'm always hungry, and when the lows are early in the morning I'm often cold and sleep-deprived as well. That's my excuse for not dissecting open one of the gonangia to see what's inside.

Even the algae are getting into the act of reproducing and recruiting. This spring I've noticed a lot of baby bullwhip kelps (Nereocystis luetkeana). Nereocystis is one of the canopy-forming kelps in subtidal kelp forests along our coast, but every year some recruit to the low intertidal. However I don't remember seeing so many baby Nereocystis thalli in the tidepools. The smallest one I saw this morning had a pneumatocyst (float) the size of a pea! In mature thalli, the float might get as big as a cantaloupe.

A baby Nereocystis thallus, at Davenport Landing
27 May 2017
© Allison J. Gong

Intertidal nursery area for Nereocystis luetkeana, Davenport Landing
27 May 2017
© Allison J. Gong

Nereocystis doesn't usually persist or get very large in the intertidal. It is more common to see detached thalli washed up on the beach than to see a living bullwhip kelp longer than about 2 meters in the intertidal. Whether or not this particular nursery area results in an established population remains to be seen. I'm betting 'No' but could very well be proved wrong. Only time will tell.

This past Monday I did something rare for me: I returned to the same intertidal site I had visited the previous day. I enjoyed myself so much the first time that I wasn't able to refuse an invitation to go out there again. The site, Pigeon Point, is one of my favorites, especially in all of its spring glory as it is now. It has always been a hotspot especially for macroalgal diversity, and so far this year appears to be living up to its reputation. The day before I collected several reds that I got to spend the next two days trying to identify.

Three intertidal gastropods at Pigeon Point. Top circular object: Thylacodes squamigerus; yellow elongated object in middle: Doriopsilla albopunctata; bottom purplish-black snail: Tegula funebralis.
1 May 2017
© Allison J. Gong

On Monday I was less overwhelmed by obsessed with algae and able to focus more on the animals, and was delighted to find a small cluster of Thylacodes squamigerus, the strange and fascinating vermetid snail. Nearby one of the vermetid snails was a yellow nudibranch (Doriopsilla albopunctata) and one of the common turban snails (Tegula funebralis). The chance proximity of three different gastropods brought to mind the incredible diversity of this group of molluscs.

The Gastropoda are the largest group within the phylum Mollusca, and can claim a fossil record that dates back to the early Cambrian, some 540 million years ago. They have been extremely successful throughout that long time and are the only molluscan group to have established lineages in both freshwater and on land (of the other molluscs, only the bivalves have made it into freshwater, with the remaining groups restricted to the sea). As you might expect, this evolutionary history has given rise to a mind-boggling array of body types and lifestyles. Let's investigate this diversity by taking a closer look at the three gastropods in the photo above.

Gastropod #1 (Thylacodes squamigerus): Very few people, on seeing this animal for the first time, would guess that it's a snail. Most would say that it's a serpulid worm. The tube is calcareous, as it is for serpulid worms, and winds around over rocks in the intertidal.

Tube of the vermetid snail Thylacodes squamigerus at Pigeon Point
1 May 2017
© Allison J. Gong

A close look at the opening of the tube, however, reveals snail-like rather than worm-like features. Thylacodes even has a snail's face, although I'll admit it isn't easy to see if you don't know to look for it. And despite crawling under a ledge with my camera, I didn't get the best view of a face. In this photo, however, you can at least see one of the cephalic tentacles:

View into the tube of Thylacodes squamigerus at Pigeon Point
1 May 2017
© Allison J. Gong

Living in a tube cemented onto a rock means that Thylacodes can't go out and find food. It must instead catch food and bring it in. Thylacodes does so by spinning threads of sticky mucus that are splayed out into the water, where they capture plankton and suspended detritus. The threads are then reeled in and everything--mucus and food--is eaten by the snail. Thylacodes tends to occur in groups, and individuals within an aggregation contribute threads to a communal feeding net, which presumably can catch more food than the sum total of all the snails' individual efforts.

Pretty unexpected for a snail, isn't it?

Gastropod #2 (Tegula funebralis): The black turban snail is probably one of the most common and commonly overlooked animals in the intertidal. People don't see them because these snails are, literally, everywhere from the high- down into the mid-intertidal. They are routinely stepped over as visitors rush to the lower intertidal, and ignored again as these same visitors leave the seashore. I love them. I keep them in the lab as portable lawnmowers for the seawater tables. They are incredibly efficient grazers, keeping the algal growth down. Plus, I think they're cute!

If there's such thing as a 'typical' marine snail, T. funebralis may very well be it. This little snail exemplifies several of the traits we use to define the Gastropoda: it lives in a coiled shell, it uses a radula for scraping algal film off rocks (yum!) and is torted. The shell is easy enough to understand, as everyone has seen a snail at some point, even if it was a terrestrial snail. The radula and torsion, however, may take a little explaining.

A congregation of Tegula funebralis at Mitchell's Cove
8 June 2016
© Allison J. Gong

Many molluscs have a radula, a file-like ribbon of teeth that can be stuck out of the mouth and used for feeding. In gastropods the radula can be a scraping organ (as in Tegula and other herbivores such as limpets), a drill (as in the predatory moon snails, which drill holes into unsuspecting clams and then slurp out their soft gooey bodies), or a poison dart (as in the venomous cone snails). The radula of a grazer such as Tegula bears many transverse rows of sharp teeth, which are regularly replaced in a conveyor belt fashion as they are worn down. This assures that the teeth being used are always nice and sharp. Remember the radula marks made by the owl limpet (Lottia gigantea)?

An owl limpet (L. gigantea) in her farm at Natural Bridges
7 March 2017
© Allison J. Gong

Tegula funebralis clearing real estate in my seawater table
27 January 2017
© Allison J. Gong

Those zig-zaggy marks are made by the scraping of the radula as the limpet crawls over her farm. Tegula funebralis makes the same type of pattern in my seawater tables. All of that white territory is area that had been scraped clean of algae in about a day. Tegula is a very industrious little snail! And they're not shy, either. I don't have to wait a day or so for them to get acclimated when I bring the back to the lab. I can move them around from table to table and after a few seconds they poke their heads out and start cruising around. I've learned from watching them over the years that they seem to have an entrained response to the rising and falling of the tides, even after I bring them into the lab. For the first few weeks of captivity, every morning when I first get to the lab I find that several Tegula have climbed up the walls. I think they're crawling up when the tide is high. I really should look at that more carefully. They never go too far, but sometimes they do drop onto the floor and I find them by stepping on them. Fortunately they are hardy creatures and the floor is always wet with seawater so as long as I find them within a day and plunk them back into the table they're fine.

Now on to torsion. Torsion is difficult to explain, but let me try. The word 'torsion' refers to the twisting of the nerve cord and some internal organs that occurs during larval development of gastropods. Here's how it works. Imagine a closed loop, like a long piece of string with the ends tied together. Lay the loop down on a table and it is just a simple loop. Pick up one end of the loop, twist it counterclockwise 180°, and lay it down again. Now you have a figure-8, right? That's not exactly what happens in the living snail, but you get the picture.

Tegula and other snails have an elongated body that is coiled and crammed to fit inside the shell. If you could take Tegula's body and stretch it out without breaking it (impossible to do, BTW), you'd see the figure-8 configuration of the nerve cord. Other internal organs are re-arranged by torsion, too. As a result, both the gill(s) and the anus now open into the mantle cavity which has been relocated over the head. This arrangement is ideal for keeping the gill(s) irrigated, but not so good for hygienic reasons. Fortunately, the mantle cavity itself is angled so that water flows through it in a more-or-less unidirectional manner, passing over the gill before the anus. Tegula and other marine snails undergo torsion while in the larval stage, and remain torted as adults. This is not the case in other gastropods, as we'll see next.

Gastropod #3 (Doriopsilla albopunctata): Everybody loves the nudibranchs, because their brilliant colors make them easy to love. Unlike the oft-undetected Thylacodes squamigerus and the ignored Tegula funebralis, many of the nudibranchs are somewhat easy to spot in the field because of their flamboyance. This is a crappy picture, but you get the point.

Doriopsilla albopunctata at Point Piños
9 May 2015
© Allison J. Gong

Doriopsilla albopunctata is one of several species of yellow dorid nudibranchs lumped together under the common name 'sea lemon'. Instead of the long fingerlike processes (cerata) that adorn the backs of the aeolid nudibranchs such as Hermissenda spp., the dorids have smooth or papillated backs that may be decorated with rings or spots. Dorids also have a set of branchial plumes on the posterior end of the dorsum; the number and color of these gills can often be used to distinguish similar species. Doriopsilla albopunctata has a smooth yellow back with little white spots, hence the species epithet (L: 'albopunctata' = 'white pointed'), and white branchial plumes.

Doriopsilla albopunctata at Franklin Point
17 July 2015
© Allison J. Gong

Nudibranchs are gastropods, although in a different group from Thylacodes and Tegula. The marine slugs, of which the nudibranchs are the most commonly encountered, are in a group called the Opisthobranchia, whose name means 'gill on back' and refers equally to the cerata of aeolids and the branchial plume of dorids. In fact, these animals lack the typical molluscan gill that the snails have. They do have a radula, however, and crawl around on a single foot exactly like Tegula does.

An adult nudibranch's body is elongated, unlike the coiled body of Tegula, and has no apparent signs of having undergone torsion. However, examination of larval nudibranchs shows that they do undergo torsion just like any other respectable gastropod. The weird thing is that some time during the transition from pelagic larva to benthic juvenile they de-tort, or untwist their innards so that their internal anatomy matches their external shape. Instead of having to poop on their own heads, nudibranchs have an anus that is sensibly located at the rear (no pun intended) of the body.

Torsion is one of those biological curiosities whose evolutionary origin is shrouded in mystery. How did such anatomical contortions evolve? Why do gastropods, and only gastropods, undergo torsion? And why do some gastropods tort as larvae, only to detort as they become adults? There are scientific hypotheses about the benefits of torsion, particularly to the larval stages, but nobody knows for sure. After all, none of use were there to watch when it happened.

This is just a tiny taste of the diversity of the Gastropoda. I think it's cool to see three such different gastropods in a small spot of the intertidal. And no doubt there were more that I didn't see. That's one of the joys of working in the intertidal: that I so often see things I wasn't even trying to find.

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