Today was the first time I've gone out on a low tide since before the whole COVID19 shelter-in-place mandates began. Looking back at my records, which I hadn't done until today because it was much too depressing, I saw that my last time out was 22 February, when the low tides were in the afternoon. At the time I made what seemed to be the not-too-bad decision to stay away from the remaining afternoon lows and wait until the spring shift to morning lows, which I like much more. And then then COVID hit and we all had to stay home and beaches were closed. So yeah, it has been much too long and I really needed this morning's short visit to the intertidal.
Beaches in Santa Cruz County are closed between the hours of 11:00 and 17:00, except that we are allowed to cross the beach to get to the water. This means that surfers, kayakers, SUP-ers, and marine biologists can get out and do their thing. Of course, my particular thing took place hours before the beach restrictions began, so I was in the clear anyway. I didn't venture too far from home, as I wasn't quite certain how easy it would be to get down to the beach.
Spring is the prime recruitment season for life in the intertidal. The algae are coming back from their winter dormancy, and areas that had been scraped clean by sand scour or winter storms are being recolonized. Many of the invertebrates have or will soon be spawning. And larvae that have spent weeks or even months in the plankton are returning to the shore to metamorphose and begin life as an adult. Just as it is on land, spring is the time for life in the sea to go forth and multiply.
For several decades now, marine ecologists have been studying barnacles and barnacle recruitment. Barnacles are a nice system for studying, for example, recruitment patterns and mortality. The cyprid larva, the larval stage whose job it is to find a permanent home in the intertidal, readily settles and metamorphoses on a variety of man-made surfaces; this makes it easy to put out plates or tiles and monitor who lands there. The fact that barnacles, once metamorphosed, remain attached to the same place for their entire lives means an ecologist can measure mortality (or survivorship, which is the inverse) by counting the barnacles every so often.
These are young barnacles (Chthamalus sp.), about 4-5 mm in diameter. I don't know how old they are, but would guess that they recruited in the past couple of months. These individuals all found a nice place to set up, because as I've written before, barnacles need to be in close proximity to conspecifics in order to mate.
This is a mixed group of Chthamalus sp. and Balanus glandula. Balanus is taller and has straighter sides and a more volcano-like appearance. Larvae of both genera recruit to the same places on rocks in the intertidal, and it is not uncommon to see assemblages like this.
Both species of barnacles are preyed upon by birds, sea stars, and snails. Predatory snails use their radula to drill a hole through the barnacle's plates and then suck out the body. Some of the barnacles in the photo below are dead--see the empty holes? Those are barnacles that were eaten by snails such as these.
What was unusual about this morning was the number of snails of the genus Acanthinucella. I don't know that I've ever seen this many of them before.
Lots of Acanthinucella means that lots of barnacles are being eaten. And empty (i.e., dead) barnacle tests are more easily dislodged from the rock than live ones are. A lot of dead barnacles could result in bare patches. And guess what? That's what I saw this morning!
And those aren't just empty spaces where nobody settled. Notice the clean edges. These empty spaces formed because barnacles were there, but died recently and fell off. The abundance of Acanthinucella may have indirectly caused these patches to form--by eating barnacles and weakening the physical structure of the population. Bare space is real estate that can be colonized by new residents. See?
These brand new recruits are about 1 mm in diameter. No doubt more will arrive in the coming months, and this patch will fill up with barnacles again. Vacant space is a limited resource in the rocky intertidal, and the demise of one generation provides opportunity for new recruits. And if the barnacles themselves don't occupy all of the space, then other animals and algae will. That's one of the things I love about the intertidal--it is a very dynamic habitat, and every visit brings something new to light. No wonder I missed it so much!
I'm willing to bet that when you think about coral, what comes to mind is something like this:
The reef-building corals of the tropics are indeed spectacular structures, incredibly rich in biodiversity and worthy of a visit if you ever get the chance. These coral colonies come in many shapes, as you can see in the photo above. Each colony consists of hundreds or thousands of tiny polyps, all connected by a shared gastrovascular cavity, or gut. The living polyps secrete a skeleton of CaCO3, which grows slowly over decades or even millennia as successive generations of polyps live their lives and then die. It's this slow accumulation of CaCO3 that makes up the physical structure of the reef.
Reef-building corals are members of the Scleractinia, the so-called stony corals. The stoniness refers to the calcareous skeleton that they all have. But not all corals live in the tropics. We actually have two species of stony corals in Northern California. The brown cup coral, Paracyathus stearnsi, lives subtidally, and I think I've seen maybe a handful in all my intertidal explorations. The orange cup coral, Balanophyllia elegans, extends up into the low intertidal, and can be very common at certain sites I visit regularly. When I see them at low tide they are emersed and look like orange blobs. But if you touch one with your finger, you can feel the hardness of the calcareous base.
Stony corals they may be, but Paracyathus and Balanophyllia are both solitary; that is, they aren't colonial. Each polyp developed from its own larva and lives its own life independent from all other corals. Its bright orange color makes Balanophyllia pretty conspicuous, even though most of them are less than 10 mm in diameter. They do occur in patches, which makes one wonder. If they're solitary rather than clonal or colonial, how do these patches arise?
To answer this question we need to venture into the lab and examine the biology of Balanophyllia more closely. Fortunately, they grow in the lab quite happily. Years ago my friend Cris collected a bunch of Balanophyllia and glued them to small tiles so they could be moved around and managed in the lab. Cris has since moved on to other things, but the corals remain in the lab to be studied. They are beautiful animals, and can't really be appreciated in the intertidal because at low tide they're all closed up. But look at how pretty they are when they're relaxed and open:
Like all cnidarian polyps, these corals have long tentacles loaded with stinging cells, or cnidocytes. See the little bumps on the otherwise translucent tentacles? Those are nematocyst batteries, clusters of stinging cells.
Let's get back to the biology of this beast and how it is that they seem to live in groups. Balanophyllia is a solitary coral with separate sexes--each polyp is either male or female. They are also brooders. Males release sperm, which are ingested by a nearby female. The female broods fertilized eggs in her gastrovascular cavity. After a long period, perhaps several months, a large reddish planula larva oozes out of the mother's mouth and crawls around for a while, generally settling and metamorphosing near its parent.
This planula is a very squishy elongate blob, and can measure anywhere from 1-4 mm in length. It is an opaque red color, has a ciliated epidermis, and lacks a mouth or digestive system. Instead of feeding, it survives on energy reserves that its mother partitioned in the egg. You might surmise that not being able to eat would necessitate a quick metamorphosis into a form that has a mouth, but you'd be wrong. While some of them do indeed settle and metamorphose very close to their parent, others crawl around for several weeks, showing no inclination to put down roots and take on life as a sessile polyp. Perhaps they can take up enough dissolved organic matter from the seawater to sustain them through a long period of fasting.
At some point, though, the larva settles and metamorphoses into a little polyp. In the lab at least, Balanophyllia larvae settle on a variety of surfaces--glass, various plastics, even the fiberglass of the seawater tables.
The little coral measures about 2 mm in diameter and has 12 tentacles. It feeds very happily on brine shrimp nauplii and should grow quickly. Those three larvae, though, may hang around forever. I got tired of waiting for them to do something and released them into the seawater system. It might or might not have been an accident.
So there we have it. Our local cold-water coral, which doesn't form reefs or live in colonies. Balanophyllia may seem atypical for corals, but what it really demonstrates is the diversity within the Scleractinia. It reminds us that generalities do indeed have some value, and that for the discerning mind it is the exceptions to the generalities that are most interesting.
Of course, sea anemones don't have faces. They do have mouths, though, and since a mouth is usually part of a face, you can sort of imagine what I'm getting at. The sunburst anemone, Anthopleura sola, is one of my favorite intertidal animals to photograph. Of the four species of Anthopleura that we have on our coast, A. sola is the most variable, which is why it keeps catching my eye.
This afternoon I met the members of the Cabrillo College Natural History Club for the low tide at Natural Bridges. Here are some of the A. sola anemones we saw.
Such an amazingly photogenic animal, isn't it?
This past Fall semester the NHC went tidepooling at Pigeon Point. Today we were at Natural Bridges, and later in the spring we are going to Asilomar. I didn't intend it, but this school year the club is getting a look at three very different intertidal sites.
It has been a while since I've spent any time in the intertidal. There isn't really any reason for this, other than a reluctance to venture out in the afternoon wind and have to fight encroaching darkness. There's also the fact that I much prefer the morning low tides, which we'll have in the spring. However, this past weekend we had some spectacular afternoon lows, and although I was working on Friday and couldn't spare the time to venture out, I went out on Saturday and Sunday.
Saturday was a special day, because I had guests with me. A woman named Marla, who reads this blog, contacted me back in the fall. She said she wanted to do something special for her husband's birthday, and asked if I'd be willing to take them to the intertidal. It turns out that Andrew's birthday was around this past weekend, and he had family coming out from Chicago to celebrate. They picked the perfect weekend, because the low tides we had were some of the lowest of the year. So on Saturday I met up with Marla, Andrew (her husband), and Betsy (Andrew's sister) and we all traipsed out to Natural Bridges.
This was our destination for the afternoon:
Taking civilians into the intertidal can be tricky, because they often come with expectations that don't get met. Like expecting to see an octopus, for example. I explain that the octopuses are there, but are better at hiding from us than we are at finding them, but that never feels very satisfactory. This trio, however, were fun to show around. The tide was beautifully low and we had fantastic luck with the weather. It had rained in the morning, but the afternoon was clear and sunny. I congratulated Marla on remembering to pay the weather bill. And the passing stormlet didn't come with a big swell, so the ocean was pretty flat. We were able to spend some quality time in the mid-tidal zone, with occasional forays into the low intertidal.
The typical Natural Bridges fauna--owl limpets, mussels, chitons, anemones, etc.--were all present and accounted for. Of course, there isn't much algal stuff going on in mid-January.
Given the time of year (mid-January) and the time of day (late afternoon), the sun was coming in at a low angle. This was tricky for photographing, both in and out of water. However, sometimes good things happen, as in this photo below:
That's a big kelp crab (Pugettia producta) nestled among four sunburst anemones (Anthopleura sola). Kelp crabs are pretty placid creatures, for crabs, and usually take cover when approached. But this one remained in plain sight, holding so still that I thought it was dead. Even when I hovered directly over it and blocked the sun, it didn't move at all. Then it occurred to me that maybe he was having the sexy times with a lady friend. So I very carefully reached down and gave him a tap on the carapace. He flinched a little, so I knew he wasn't dead, but made no move to get away. And I caught a glimpse of a more golden leg underneath him.
Crabs live their entire lives encased in a rigid exoskeleton, and can mate only during a short window of opportunity after a female molts. Early in the breeding season, a female crab uses pheromones to attract nearby males. When a suitable male approaches, she may let him grab her in a sort of crabby hug. That's what this male kelp crab is doing to his mate. They may remain in this embrace for several days, waiting until the female molts and her new exoskeleton is soft. At that point the male will use specialized appendages to insert packets of sperm into the female's gonopores. The two will then go their separate ways.
We didn't disturb these crabs, and let them go on doing their thing. By now the sun was going down, so we headed back up and were rewarded with a glorious sunset.
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.
A few weeks ago I was contacted by a woman named Kathleen, who reads this blog and is herself a student of the seaweeds. She said that she studies a site up at Pescadero, about an hour up the coast from me. We decided to meet up during the series of low tides around the Fourth of July so we could explore the area together, and she could help me with my algal IDs. My friend and former student, Lisa, joined us for the fun.
The most prominent landmark along the coastline in this region is Bird Island, which is accessible only at minus tides, when it is revealed to be a peninsula. It smells pretty much as you probably imagine, especially if you happen to be downwind. Given the prevailing wind direction, that means that the closer you get to Bird Island from the south, the stronger the smell. Kathleen's site is the south side of Pescadero Point, fortunately far enough south of Bird Island that the smell isn't noticeable from that distance. She has a permanent transect that she surveys regularly, taking note of algal abundances and distributions.
One of the notable things we all noticed was the conspicuous presence of big, healthy ochre stars (Pisaster ochraceus)--many hand-sized or larger. I also saw many smaller stars, in the 2 cm size range, but these were hidden in crevices or under algae. The big guys and gals, were out there in plain sight.
However, not all was perfect for the sea stars at Pescadero Point. One of the ochre stars showed symptoms of sea star wasting syndrome (SSWS). It had autotomized two of its arms and had a sloppy, goopy open wound that extended into the oral disc. It was also mushy when I touched it and didn't firm up the way healthy stars do. This star is a goner, even though it doesn't know it yet. That's the beauty (and in this case, tragedy) of an entirely decentralized nervous system.
After I mentioned having seen a sick sea star we compared notes on the current status of SSWS. What more do we know about the syndrome, and any recovery of stars? We came to the consensus that the oubreak was probably caused by a perfect storm of ecological conditions--an opportunistically pathogenic virus that is ubiquitous in the environment, environmental stresses, and high population densities both intertidally and subtidally. Kathleen asked me what I had been seeing recently. I told her that Pisaster ochraceus, one of the species that melted away in spectacular fashion, seems to be making a strong comeback in the places where I used to see it in large numbers. Even though every once in a while i see a sick star, places like Natural Bridges and Davenport Landing are again populated by lots of hand-sized-or-bigger ochre stars. Which of course brings up the question of where these large stars suddenly came from. I think they were tiny stars when the outbreak occurred, hiding in the mussel beds. Many of them died, but as with any plague there are always some survivors. Those lucky few managed to hang on and creep into the niches that opened up when so many adults died. But would little juveniles only a few millimeters in diameter be able to grow to the sizes that we're seeing now, in ~5 years? I suppose that's not out of the question, and we know that when fed well in the lab they grow very quickly, but individual growth rates in the field are difficult to measure.
Another animal goody that we saw were clusters of the bryozoan, Flustrellidra corniculata. Unlike most bryozoans, which are calcified and crunchy, Flustrellidra colonies are soft and flexible. They look more like strange, thick pieces of brown algae than anything recognizable as a bryozoan.
We were there to do some basic marine botany, and although I kept getting distracted by the invertebrates I did also pay attention to the floral aspect of Kathleen's site. She pointed out that Laminaria sinclairii, one of the small low-intertidal kelps, was always abundant. It's true, there were rocks that were entirely covered with L. sinclairii, like this one:
Laminaria sinclairii and L. setchellii are the most common intertidal species of the genus on our coast. They are easily distinguishable because L. sinclairii has a single undivided blade arising from the stipe, and L. setchellii has a blade that is subdivided into fingerlike sections; in fact, the former species epithet for L. setchellii was dentigera, referring to 'finger'.
See the difference?
There is a third species of Laminaria on our coast, that I knew only by reputation. What I'd heard is that Laminaria ephemera resembles L. sinclairii except for the morphology of the holdfast: L. ephemera has a discoid, suction-cup holdfast while L. sinclairii has the more typical hapterous holdfast (made of intertwined cylindrical projections). I think I might have seen a few L. ephemera at Pescadero. These thalli appear to have suction-cup holdfasts, don't they?
We didn't spend much time on the south side of the point, but scrambled over the rocks to the north side, where there are stretches of sandy beach between rocky outcrops. Bird Island is that peninsula in the top of the picture. As I mentioned above, it is connected to the beach only at low tide, so while I think of it as a peninsula, it really is an island most of the time.
Once on the north side of the point we slowed down and made some more attentive observations of the flora. It turns out that this portion of our intertidal visit was sponsored by the letter 'P'. One of the things we all noticed was the prevalence of Pyropia, the filmy red alga that is common in the high-mid intertidal. The thallus of Pyropia consists of a single layer of cells connected to form a very thin elastic tissue. It dries to a crisp in the sun, but rehydrates when the tide returns. You've probably encountered Pyropia before without realizing it: nori is made of Pyropia that has been shredded and processed into paper-like sheets, used for things like sushi rolls.
Although it looks uniformly blackish-green when packaged for human consumption, Pyropia's color in life is a glorious iridescent mixture of greens, olives, and purples. It is another of those easily overlooked denizens of the intertidal that deserves a much closer look than it usually gets.
Another common red alga at Pescadero Point is the delicate and lacy Plocamium cartilagineum. This is one of the hobbyist phycologist's favorite species because it presses like a dream and makes great gifts or wall decorations. As I wrote about here, Plocamium has a doppelganger: Microcladia coulteri. These algae share a similar morphology, but as I mentioned in the previous post, natural history makes it easy to distinguish between the two in the field. Microcladia is epiphytic, growing on other algae, and Plocamium is not.
Plocamium grows on rock surfaces in the mid-to-low tide regions. It sometimes gets surrounded or even buried in sand, but if you dig down far enough you'll always find the holdfast attached to a rock (or shell or other hard object).
Last month I wrote about Postelsia palmaeformis, the sea palm. We found a most handsome specimen washed up on the beach. Note that, as per usual, it wasn't the holdfast of the kelp that failed. The holdfast did its job perfectly well, and it was the mussel it was attached to that broke free of the rock.
The sad thing about finding great specimens like this on the beach is the realization that it will soon be dead. In fact, so will the mussel. Such is the price organisms pay for failing to hang onto their substrate (or for their substrate's failure to hang on). The rocky intertidal is a harsh place to live, and can be unforgiving of mistakes and bad decisions.
That's part of the reason I find it so fascinating. Most wild organisms live on the knife-edge of survival, with only the thinnest margin between life and death. Every organism has its predators, pathogens, and parasites to deal with on a daily basis, in addition to the physical stresses of its habitat. All of the organisms that I study in the intertidal are marine--not freshwater or even brackish, although some can tolerate reduced salinity (and on the other extreme, some tolerate very high salinity). They evolved to live in the ocean, in a habitat where the ocean abandons them for a few hours twice a day. Yet as improbable as that sounds, the diversity in the intertidal is astonishingly high. Obviously, for those that can live there, the trade-off between stability and safety is worthwhile. Nature will always find a way.
Be honest now. When you think of clams, what comes to mind? If you're like most people, visions of clams steamed in white wine, garlic, and butter might dance in your head. Or perhaps clams in cioppino or a hearty chowder would be your go-to. In any case, I doubt that clams, as actual living creatures, occupy much of your brain. Because let's face it, at first glance even living clams aren't the most energetic and charismatic animals. Most of the really cool things that they do, like suck water through their shells for filter feeding and gas exchange, they do while buried in the mud.
When you think about it, though, just the fact that clams live in the sand or mud while depending on water that may be quite far from them is rather amazing. All animals require oxygen, and for marine animals that oxygen comes from seawater. Animals that move freely through the water have access to a ready supply of oxygen. But clams live more or less fixed lives encased in sediment, and water can be quite far from their bodies. How, then, do they pull water into their shells and across their gills? They use siphons, which can reach up to the surface of the sediment into the water column.
A clam has two siphons--one pulls clean water into the shells and the other expels water from the shells. This arrangement allows for one-way flow across the gills, which serve double duty as both feeding and gas exchange organs. The siphons themselves are somewhat muscular and can open and close, but it's the ciliary action of the gills that create the actual water current. In a living clam the only visible body parts are the siphons, which in some species (e.g., geoducks) are so large that they cannot be entirely withdrawn into the shells.
Of the two siphons in the picture above, can you tell which is the incurrent and which is the excurrent? What do you think is the functional significance of that network of white structures that cover the opening of one of the siphons?
Not only do clams live buried in sediment, but some of them can actually bore into rocks. These boring clams, the pholads, have shells that are morphologically and functionally different from the typical clams you've encountered in cioppino. They are elongated on the anterior-posterior axis and the anterior ends are heavily sculpted and fortified to grind into rock. Of course, they can do this only in areas where the rock is soft--you don't see pholads burrowed into granite, for example.
Fortunately for the pholads, much of the rock in the Santa Cruz area is a soft mudstone, easily eroded and burrowed into. I've seen pholads at intertidal sites from Capitola to Davenport. Both dead pholads and live pholads can be seen, but it takes a careful eye to spot the live ones. Of course, all you'd ever see of a living pholad is the siphons. When the animal dies, though, the shells are left behind. As the mudstone continues to erode the shells can be exposed, just like fossils. And as a matter of fact, the mudstone formations around here are known for their fossil contents. I think, but am not certain, that these empty shells in holes belong to Parapholus californica.
How does a clam burrow into even soft rock? A description of burrowing activity of Parapholus californica can be read here. As you can imagine, it's a slow and continuous process. Fortunately, these clams don't have much else going on and can take their time. In some ways, their lifestyle sounds pretty ideal: hang out in a snug burrow where predators can't get at your soft body and extend your siphons out to bring in clean water for food and oxygen. Sure, when it comes to reproduction the only option available is free-spawning and hoping for the best, but that has proven to be a successful strategy for countless generations of your kind. Aside from the cost of making gametes, it's a pretty low-energy way to produce offspring. Maybe the old saying "happy as a clam" isn't that far off the truth.
Professor Emeritus John Pearse has been monitoring intertidal areas in the Monterey Bay region since the early 1970s. Here on the north end of Monterey Bay, he set up two research sites: Opal Cliffs in 1972 and Soquel Point in 1970. These sites are separated by about 975 meters (3200 feet) as the gull flies. My understanding is that the original motivation for studying these sites was to compare the biota at Soquel Point, which had a sewage outfall at the time, with that at Opal Cliffs, which did not. The sewer discharge was relocated in 1976, and the project has now morphed into a study of long-term recovery at the two sites. In the decades since, John has led students, former students, and community members to conduct Critter Counts at these sites during one of the mid-year low tides. Soquel Point is visited on the first day, and Opal Cliffs is visited the following day. When John founded the LiMPETS rocky intertidal monitoring program for teachers and students in the 1990s, the Soquel Point and Opal Cliffs locations were incorporated into the LiMPETS regime.
I have participated in the annual Critter Counts off and on through the years--around here, one takes any chance one gets to venture into the intertidal with John Pearse! I usually have my own plans for this series of low tides, but try to make at least one of the Critter Count mornings. This year (2019) the first 16 days of June have been designated the official time frame for Snapshot Cal Coast, giving marine biologists and marine aficionados an excuse to go to the ocean and make observations for iNaturalist. I had set myself the goal of submitting observations for every day of Snapshot Cal Coast, knowing that every day this week would be devoted to morning low tides. That's the easy part. Next week, when we lose the minus tides, I'll do other things, like look at plankton or photograph seabirds. My plans for this week included a trip to Franklin Point on Wednesday and doing the Critter Count at Opal Cliffs on Thursday. John asked me if I could also do the Wednesday Critter Count. As I alluded above, I'm not going to say "No" to an invitation like that! So I didn't make it out to Franklin Point to document the staurozoans for Snapshot Cal Coast, but that's okay. Some plans are meant to be changed.
Day 1- Soquel Point
Both the Soquel Point and Opal Cliffs sites are flat benches with little vertical topography. The benches are separated by channels that retain water as the tide recedes. The Soquel Point site has deeper channels that make the benches more like islands than connected platforms.
The benches are pretty easy to get around on, as long as you remember that surfgrass (Phyllospadix spp.) is treacherous stuff. The long leaves are slippery and tend to cover pitfalls like unexpected deepish holes. The difficulty at this site is that it takes very little rise in the tide for water in the channels to get deep. You can be working along for a while, then get up to leave and realize that you're surrounded by water. Keeping that caveat in mind, we worked fast.
For the Critter Count we keep tabs on only a subset of the organisms in the intertidal. The quadrat defines our sample; we put it down at randomly determined coordinates within a permanent study area. Some animals, such as anemones, turban snails, and hermit crabs, are counted individually. For other organisms (surfgrass, algae, Phragmatopoma) we count how many of the 25 small squares they appear in. Some quadrats are pretty easy and take little time; others, such as ones that are placed over channels or pools, are more difficult and take much longer.
Because of the rising tide I didn't have a lot of time to look around and take photos of the critters we were counting. Linda and I were worried about finishing our quadrats before the channels got deep enough to flood our boots. But here are two of the things that caught my eye:
Day 2 - Opal Cliffs
The next day we met a half hour later and a few blocks down the road. The Opal Cliffs site is a popular spot with surfers: If you've ever heard of the surf spot Pleasure Point or seen the movie Chasing Mavericks, you know about this location. As far as the intertidal goes, it's an easy site to study. The channels aren't as deep as those at Soquel Point so we could work at a more leisurely pace. As the rest of the group hauled up all the gear and left to get on with their day, I stayed behind to take pictures for my iNaturalist observations. The sky was overcast, making for good picture-taking conditions. I'll just add a gallery of photos to share with you.
There is one critter that deserve more attention here, because I'd never seen one in the intertidal before. Two of the guys finished their quadrats early and started flipping over rocks to look for an octopus. To my knowledge they didn't find any octopuses, but they did find a bizarre fish. At first it didn't look like much:
Hannah, the LiMPETS coordinator for Monterey and Santa Cruz Counties, recognized the fish right away and grabbed it by the body. She held it up so we could see the ventral surface.
This is a plainfin midshipman. These are nearshore fish found in the Eastern Pacific from Alaska to southern Baja. Clearly, I need to spend more time flipping over big rocks! The midshipman is a noctural fish, resting in the sand during the day and venturing out to feed at night. Like many nocturnal animals, it is bioluminescent--those white dots on the fish's belly in the photo above are photophores. Midshipmen are heavily decorated with photophores all over the body. This bioluminescence is used both for predator avoidance and mate choice.
The lives of plainfin midshipmen and human beings intersect in the wee hours of the morning. During breeding season these fish sing or grunt. They breed in intertidal areas, where females lay eggs in nests that are subsequently guarded by males. Both sexes make noise, but it's the breeding males that are the noisiest. They grunt and growl at each other when fighting for territory, but hum when courting females. Females typically grunt only when in conflict with others. People who live in houseboats on the water in Sausalito have reported strange sounds emanating from the water beneath them, only to learn that what they hear are the love and fight songs of fish!
I've always been a fan of the intertidal fishes. They seem to have a lot of personality. Plus, any aquatic animal that lives where the water could dry up once or twice a day deserves my admiration. Of course, all of the invertebrates also fall into this category, which may explain why I find them so fascinating.
After we admired the midshipman's photophores and impressive teeth, we put it back in the sand and replaced the rock on top of it. It was probably happy to get back to snoozing away the next few hours before the tide returned. I don't know how I never realized the midshipmen were in the intertidal. I think I just assumed that they were in deeper water. Now that I know where to find them, I will spend more time flipping over rocks. And who knows, maybe I'll even find an octopus!
If, like me, you are fortunate enough to live near the coast in Northern California, you get to visit the tidepools. And when you do, you may notice something that looks like a pile of sand in the mid tidal zone below the mussel beds. When you venture down and touch the sand, you'll find that it's hard--hard enough to walk on, if you step very carefully, but also somewhat brittle.
It might look something like this:
Meet Phragmatopoma californica, the sandcastle worm. Hard to believe that these mounds, which can be the size of a small dining room table, are constructed by little worms, isn't it? Phragmatopoma is one of the many marine segmented worms grouped together as the Polychaeta. We have lots of polychaetes on our coast, ranging in size from greater-than-hand-length nereids and glycerids that can take a bite out of you and draw blood, to tiny worms small enough to swim in the layer of water between sand grains. In fact, the majority of our worm fauna on the coast consists of polychaetes.
Polychaetes make up a large and very diverse taxon, comprising some 80 or so families. Polychaete taxonomists might argue against it, but to make things simpler, we can divide them into two subclasses, the Errantia and the Sedentaria. As the name implies, the Errantia comprises the worms that are errant, or free-crawling. That said, most of them don't actually crawl around in plain sight; they tend to burrow in sediment, shell debris, or gravel, or wiggle their way through various benthic faunal communities. Some of them make temporary shelters by wrapping themselves in pieces of algae sewn shut with mucus threads. The Sedentaria, on the other hand, are pretty much all, well, sedentary. They live in more or less permanent tubes made of various materials, and generally can't live outside of them.
Phragmatopoma is very much a sedentary worm. It lives in a tube that it builds out of sand grains. Yes, this little worm is a mason!
What you see in these mounds is an aggregation of hundreds of individual worms. The mounds do not form by accident or chance. Phragmatopoma has a planktonic larval stage that floats around on ocean currents for some weeks before returning to the shore. The larva is attracted to areas already colonized by members of their species, which it detects by sniffing out the chemical signal of the glue used to create the tubes (more on that below). This phenomenon is called gregarious settlement. If you consider the challenge of being a tiny creature searching the entire coastline for a place to settle and live forever, one big clue as to the suitability of a given location is the presence of conspecific adults. After all, if your parents' generation grew up there, chances are it's a good spot for you to grow up, too.
Each of those holes in the big sandy mound is the entrance to a worm's tube. Tubes might be as long as 15 cm, but the worm itself is much smaller: a whopping big one would be 4 cm long, and most are in the 2-3 cm size range. From this pair of observations I infer that the worms can and do move up and down the tube. They have to move to the open end of the tube to feed, and can withdraw towards the closed end to avoid predators, or seek protection from desiccation.
Phragmatopoma's tube is not a haphazardly constructed object. It is the worm's home for the entirety of its post-larval life, and is constructed to shield its builder/occupant from the mechanical bashing that occurs twice daily as the tide floods and ebbs. As such, it must be strong and able to maintain its structural integrity. Let's take a closer look at an isolated tube under the dissecting scope:
The tube itself is made of debris--sand grains, bits of shell, the occasional tiny sea urchin spine--that the worm gathers from its environment. Glandular regions at the worm's anterior region secrete around the body a cylinder of sticky cement that is chemically similar to both spider silk and the byssal threads that mussels use to attach themselves to rocks in the intertidal. The inside of the tube is lined with a chitin-like material. The worm uses tentacles on its head region to collect and sort the 'stones' and glues them to the outside of the lining. There is some degree of selection involved; in the photo above you can see that all of the sand grains are more or less the same size, with none standing out as being conspicuously smaller or larger than the others. Growing worms that are actively building their tubes may be geographically restricted at least partly by the availability sand grains of the right size; if the sand is too fine or too coarse, the worm's either can't or don't live there.
Life inside a tube
Living in a tube may provide significant protection from wave bashing and predators, but does present some challenges as well. One thing that comes to mind is the matter of personal hygiene: What happens to the worm's poop? As we know, the worm lives inside the tube but it not attached to it, and can crawl up and down within it. To understand how it does, we have to review some basics of polychaete anatomy.
The word 'polychaete' comes from Greek ('many bristles') and refers to the fact that these segmented worms have chaetae, or bristles, along the left and right sides of the body. In some worms the segments, including chaetae, are pretty much the same from the anterior end of the body to the posterior end. In others, the segments and chaetae are differentiated from one body region to another. In the case of Phragmatopoma, all you can see sticking out of a tube is the head region, consisting of the slender feeding tentacles and a large disc-shaped structure called an operculum, which made of fused cephalic chaetae and serves as a door to close off the tube when the worm withdraws. Behind the head is a collar region, a series of three adjacent segments that have very stiff chaetae that can be pushed out against the lining of the tube to anchor the body in place. The rest of the body behind the collar is the trunk, which bears smaller chaetae on each segment. The entire epidermis is ciliated, which keeps water flowing around the body.
But what about the poop? As in most vermiform animals, Phragmatopoma's anus is at the posterior end of the body, which is oriented towards the closed end of the tube. How, then, does it defecate without fouling its home? The answer is both simple and ingenious. Phragmatopoma has a long rectum, which is curved to run anteriorly back towards the head. The anus, located at the terminal end of the rectum, discharges fecal pellets about halfway up the length of the body. The ciliary currents of the epidermis then flush the fecal pellets the rest of the way up the tube and out the top.
The skinny cylindrical things in the photo below are Phragmatopoma's fecal pellets!
Gas exchange is another challenge for animals that live within tubes. Aquatic animals exchange respiratory gases with the water that surrounds them, which is easy for animals that live where the water is constantly moving over their bodies. But for tube-dwellers, gas exchange is much more difficult. Phragmatopoma has paired gills on each segment of the trunk region of the body, which greatly increase the surface area for gas exchange. Any gas exchange surface is useless unless it connects with the circulatory system, so blood vessels flow into and out of each gill. Dissolved oxygen diffuses from the water into the blood, and is then circulated throughout the body. A certain amount of gas exchange probably occurs across the surface of the tentacles, too. To make things easier, the ciliated epidermis of the body keeps that small amount of water inside the tube moving, minimizing stagnation. When the worm's head is extended out for feeding, the tube is flushed with clean water. When the worm is withdrawn into the tube at low tide, its only oxygen supply is in the water contained in the tube with it. Like most of its intertidal neighbors, Phragmatopoma hunkers down and waits for the tide to return, when it can feed and breathe more easily.
And speaking of feeding, I should mention that Phragmatopoma is a filter feeder. Those purple tentacles are ciliated and create a water current that brings small suspended particles towards the mouth located at the base of the tentacles. In the video below the operculum is the darker object to the left; it represents the dorsal side of the worm's body. The long, filiform tentacles are the feeding tentacles.
As you may imagine, living in a tube also affects the way that Phragmatopoma reproduces. The worms never leave their tubes, so copulation isn't an option for them. Despite their occurrence in large groups they are not clonal, and reproduce only sexually. Both sexes of Phragmatopoma spawn gametes into the water, where fertilization and larval development take place. Living in dense aggregations and spawning at the same time as everyone else maximizes the chance that egg and sperm of the same species will find each other. Many marine invertebrates throughout the oceans, from corals to sea urchins, spawn synchronously. After all, it does an individual no good to throw gametes out into the world if it is the only one of its type around--all of the metabolic energy that went into producing and maintaining the gametes would be entirely wasted.
Clearly, the advantages of living in a tube outweigh the costs and inconveniences. Phragmatopoma has evolved physiological, anatomical, and behavioral adaptations to deal with life in the intertidal. One of those adaptations is the tube, which solves one set of problems but creates others which also need to be solved if the animal is to survive. Evolution comes up with solutions like this all the time. Every trait has metabolic and/or fitness costs, and an organism's biology is based on this type of evolutionary compromise. Life in the intertidal is a tough game. It is probable that none of the various biological processes that keep Phragmatopoma alive work function quite as well as they could, if they were isolated systems. But inside the bodies of these little worms, everything works just well enough for them to be one of the more conspicuous inhabitants of the intertidal.