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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.

Map of the Pescadero Point region
05 July 2019
© Google

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.

South side of Pescadero Point
05 July 2019
© Allison J. Gong

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.

Constellation of ochre stars (Pisaster ochraceus) at Pescadero Point
05 July 2019
© Allison J. Gong

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.

Sick ochre star (Pisaster ochraceus) at Pescadero Point
05 July 2019
© Allison J. Gong

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.

Flustrellidra corniculata at Pescadero Point
05 July 2019
© Allison J. Gong

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 at Pescadero Point
05 July 2019
© Allison J. Gong

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'.

Laminaria setchellii at Franklin Point
15 June 2018
© Allison J. Gong

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?

Laminaria ephemera(?) at Pescadero Point
05 July 2019
© Allison J. Gong
North side of Pescadero Point
05 July 2019
© Allison J. Gong

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.

Pyropia sp. at Pescadero Point
05 July 2019
© Allison J. Gong
Plocamium cartilagineum at Pescadero Point
05 July 2019
© Allison J. Gong

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.

Postelsia palmaeformis at Pescadero Point
05 July 2019
© Allison J. Gong

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.

Siphons of a pholad bivalve at Pleasure Point
16 July 2018
© Allison J. Gong

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.

Pholad siphons at Pleasure Point
16 July 2018
© Allison J. Gong

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.

Pholad shells at Natural Bridges
8 June 2019
© Allison J. Gong

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.

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