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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 largest polyps in the phylum, 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 now 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 weekend I was supposed to take a photographer and his assistant into the field to hunt for staurozoans. I mean a real photographer, one who has worked for National Geographic. He also wrote the book One Cubic Foot. You may have heard of the guy. His name is David Liittschwager. Anyway, his assistant contacted me back in March, saying that he was working on something jellyfish-related for Nat Geo and hoped to include staurozoans in the story, and did I know anything about them? As in, maybe know where to find them? It just so happens that I do indeed know where to find staurozoans, at least sometimes, and we made a date to go hunting on a low tide. Then early in May the assistant contacted me to let me know that David's schedule had changed and he couldn't meet me today, and she hoped they'd be able to work with me in the future, and so on.

None of which means that I wouldn't go look for them anyways. I'd made the plans, the tide would still be fantastic, and so I went. And besides, these are staurozoans we're talking about! I will go out of my way to look for them as often as I can. Not only that, but I hadn't been to Franklin Point at all in 2018 and that certainly needed to be remedied.

Pigeon Point, viewed from Franklin Point trail
19 May 2018
© Allison J. Gong

The sand has definitely returned. The beach is a lot less steep than it was in the winter, and some of the rocks are completely covered again. This meant that the channels where staurozoans would likely be found are shallower and easier to search. But you still have to know where to look.

Tidal area at Franklin Point
19 May 2018
© Allison J. Gong

See that large pool? That's where the staurozoans live. They like areas where the water constantly moves back and forth, which makes them difficult to photograph in situ. And given that the big ones are about 2 cm in diameter and most of them are the same color as the algae they're attached to, they're a challenge to find in the first place. I looked for a long time and was about to give up on my search image when I found a single small staurozoan, about 10 mm in diameter, quite by accident. It was a golden-brown color, quite happily living in a surge channel. I took several very lousy pictures of it before coming up with the bright idea of moving it up the beach a bit to an area where the water wasn't moving quite as much. I sloshed up a few steps and found a likely spot, then placed my staurozoan where the water was deep enough for me to submerge the camera and take pictures.

Staurozoan (Haliclystus sp.) at Franklin Point
19 May 2018
© Allison J. Gong
Staurozoan (Haliclystus sp.) at Franklin Point
19 May 2018
© Allison J. Gong

Cute little thing, isn't it? I had my head down taking pictures of this animal, congratulating myself on having found it. When I looked around me I saw that I had inadvertently discovered a whole neighborhood of staurozoans. They were all around me! And some of them were quite large, a little over 2 cm in diameter. All of a sudden I couldn't not see them.

Staurozoan (Haliclystus sp.) at Franklin Point
19 May 2018
© Allison J. Gong

I know I've seen staurozoans in the same bottle green color as the Ulva, but this time I saw only brown ones. As you can see even the animals attached to Ulva were brown. Staurozoans seem to be solitary creatures. They are not permanently attached but do not aggregate and are not clonal. Most of the ones I found were as singles, although I did find a few loose clusters of 3-4 animals that just happened to be gathered in the same general vicinity.

Trio of staurozoans (Haliclystus sp.) at Franklin Point
19 May 2018
© Allison J. Gong

Not much is known about the biology of Haliclystus, or any of the staurozoans. I collected some one time many years ago, and brought them back to the lab for closer observation. They seemed to eat Artemia nauplii very readily, and I did get to observe some interesting behaviors, but they all died within a week or so. Given that I can find them only in certain places at Franklin Point, they must be picky about their living conditions. Obviously I can't provide what they need at the marine lab. The surging water movement, for example, is something that I can't easily replicate. I need to think about that. The mid-June low tides look extremely promising, and my collecting permit does allow me to collect staurozoans at Franklin Point. Maybe I'll be able to rig up something that better approximates their natural living conditions in the lab.

In the meantime, I just want to look at them.

Staurozoan (Haliclystus sp.) at Franklin Point
19 May 2018
© Allison J. Gong
Pair of staurozoans (Haliclystus sp) at Franklin Point
19 May 2018
© Allison J. Gong

For several centuries now, Earth's only natural satellite has been associated with odd or unusual behavior. Lunatics were people we would describe today as mentally ill, who behaved in ways that couldn't be predicted and might be dangerous. The erratic behaviors were attributed to the vague condition of lunacy. These words are derived from the Latin luna, which means 'moon'. The cycles of the moon have long been thought to influence human behavior as well; hence such legends as the werewolf.

We do know that the moon indeed has a very strong influence on aspects of many organisms, primarily through the tides. For example, reproduction in many marine animals is timed to coincide with a particular point in the tidal cycle. Grunion (Leuresthes tenuis, small, silver, finger-shaped fishes) run themselves up onto California beaches at night to spawn following the full and new moon high tides in the early summer months. Corals in the Great Barrier Reef spawn together in the handful of nights after the full moon in November. Animals such as these, which reproduce via broadcast spawning, are the ones most likely to benefit from synchronized spawning; after all, there is no point in spawning if you're the only one doing it. Invertebrates don't have watches or calendars; they keep time by sensing the natural cycles of sun and moon. The moon's strong effect on the tides is a signal that all marine creatures can sense and use to coordinate spawning, increasing the probability of successful fertilization for all.

Last night, Wednesday 6 September 2017, the moon was full. Yesterday at the lab, I noticed that  the large Anthopleura sola anemones living in the corner of my table had spawned.

A male Anthopleura sola anemone that had spawned
6 September 2017
© Allison J. Gong

That diffuse grayish stuff in the right-hand side of the photo is a pile of sperm. I looked at a sample under the microscope, just to be sure. By this time they had been sitting at the bottom of the table for several hours and most of them were dead. But they were definitely sperm:

Whenever I see something unusual like this my first impulse is to see if it's happening anywhere else at the lab. So I started poking around. The aquarists at the Seymour Center told me that some of their big anemones had spawned in the past couple of days; however, since they clean and vacuum the tanks every day all evidence was long gone.

Fortunately there are several A. sola anemones in other labs that aren't cleaned as regularly as the public viewing areas. One of the animals in the lab next door to where I have my table had also spawned. . .

Female Anthopleura sola
6 September 2017
© Allison J. Gong

. . . and this one is a female! What looks like a pile of fine dust is actually a pile of eggs.

Eggs of Anthopleura sola
6 September 2017
© Allison J. Gong

And the eggs are really cool. See those spines? They are called cytospines and apparently deter predation. Other species in the genus Anthopleura (A. elegantissima and A. xanthogrammica) are known to have spiny eggs, so it appears that this is a shared feature. Now, if only I could get my hands on eggs of the fourth congeneric species--A. artemisia, the moonglow anemone--that occurs in our area, I'd know for certain, at least for California species. I examined the eggs under higher magnification, but due to their opacity I couldn't tell if the had been fertilized. Most appeared to be solid single undivided cells; they could, however, be multicellular embryos.

All told, of the anemones that had obviously spawned, 1 was female and 4 were male. I sucked up some of the eggs and put them in a beaker of filtered seawater. I doubt that anything will happen, but I may be in for a pleasant surprise when I check on them tomorrow.

Last week I went up to Davenport to do some collecting in the intertidal. The tide was low enough to allow access to a particular area with two pools where I have had luck in the past finding hydroids and other cool stuff. These pools are great because they are shallow and surrounded by flat-ish rocks, so I can lie down on my stomach and really get close to where the action is. At this time of year the algae and surfgrasses are starting to regrow; the surface of the pools was covered by leaves of Phyllospadix torreyi, the narrow-leafed surfgrass.

Parting the curtain of Phyllospadix leaves to gaze into the first pool I was pleasantly surprised to find this. What does it look like to you?

Aglaophenia latirostris at Davenport Landing
8 March 2017
© Allison J. Gong

There are actually two very different organisms acting as main subjects in this photo. The pink stuff is a coralline alga, a type of red alga that secretes CaCO3 in its cell walls. Coralline algae come in two different forms: one is a crust that grows over surfaces and the other, like this, grows upright and branching. Because they sequester CaCO3, corallines are likely to be affected by the projected increase of the ocean's acidity due to the continued burning of fossil fuels. Ocean acidification is one of the sexy issues in science these days, and although it is very interesting and pertinent to today's world it is not the topic for this post. Suffice it to say that changes in ocean chemistry are making it more difficult for any organisms to precipitate CaCO3 out of seawater to build things like shells or calcified cell walls.

It's the tannish featherlike stuff in the photo that I was particularly interested in. At first glance the tan thing looks like a clump of a very fine, fernlike plant. It is, however, an animal. To be more specific, it is a type of colonial cnidarian called a hydroid. I love hydroids for their hidden beauty, not always visible to the naked eye, and the fact that at first glance they so closely resemble plants. In fact, many hydroid colonies grow in ways very similar to those of plants, which has often made me think that in some cases the differences between plants and animals aren't as great as you might assume. But that's a matter for a separate essay.

I collected this piece of hydroid and brought it back to the lab. The next day I took some photos. To give you an idea of how big the colony is, the finger bowl is about 12 cm in diameter and the longest of these fronds is about 3 cm long.

Colony of the hydroid Aglaophenia latirostris
9 March 2017
© Allison J. Gong

And here's a closer view through the dissecting scope.

The colonial hydroid Aglaophenia latirorostris
9 March 2017
© Allison J. Gong

Each of the fronds has a structure that we describe as pinnate, or featherlike--consisting of a central rachis with smaller branches on each side. This level of complexity can be seen with the naked eye. Zooming in under the scope brings into view more of the intricacy of this body plan:

Close-up view of a single frond of Aglaophenia latirostris, showing feeding polyps and two gonangia
9 March 2017
© Allison J. Gong

At this level of magnification you can see the anatomical details that cause us to describe this animal's structure as modular. In this context the term 'modular' refers to a body that is constructed of potentially independent units. A colony like this is built of several different types of modules called zooids, some of which are familiarly referred to as polyps. Each zooid has a specific job and is specialized for that job; for example, gastrozooids are the feeders, while gonozooids take care of the sexual reproduction of the colony. In this colony of Aglaophenia each of these side branches consists of several stacked gastrozooids, which you can see as the very small polyps bearing typical cnidarian feeding tentacles. Aglaophenia is a thecate hydroid; this means that each gastrozooid sits inside a tiny cup, called a theca, into which it can withdraw for protection. Those larger structures with pinkish blobs inside are called gonangia. A gonangium is a modified gonozooid, found in only thecate hydroid colonies, that contains either medusa buds or other reproductive structures called gonophores.

Pretty complicated, isn't it? Who would expect such a small animal to have this much anatomical complexity?


In the second pool I found an entirely different type of hydroid. At first glance this one looks more animal-like than Aglaophenia does, although it is still a strange kind of animal. This is Sarsia, one of the athecate hydroids whose gastrozooids do not have a protective theca. It might be easier to think of these and other athecate hydroids (such as Ectopleura, which I wrote about here and here) as naked, with the polyps not having anywhere to hide.

Colony of the athecate hydroid Sarsia sp.
9 March 2017
© Allison J. Gong

Each of these polyps is about 1 cm tall. The mouth is located on the very end of the stalk. The tentacles, not quite conforming to the general rule of cnidarian polyp morphology, do not form a ring around the mouth. Instead, they are scattered over the end of the stalk.

Here's a closer view:

Colony of the athecate hydroid Sarsia sp.
9 March 2017
© Allison J. Gong

In the hydroid version of Sarsia, the reproductive gonozooids are reduced to small buds that contain medusae. You can see a few round pink blobs in the lower right of the colony above; those are the medusa buds.  The medusae are fairly common in the local plankton, indicating that the hydroid stage is likewise abundant. Here's a picture of a Sarsia medusa that I found in a plankton tow in May 2015.

Medusa of the genus Sarsia
1 May 2015
© Allison J. Gong

The medusa of Sarsia is about 1 mm in diameter and has four tentacles, which usually get retracted when the animal is dragged into a plankton net. Sometimes, if the medusa isn't too beat up, it will relax and start swimming. I recorded some swimming behavior in a little medusa that I put into a small drop of water on a depression slide. It refused to let its tentacles down but you might be able to distinguish four tentacle bulbs.

There's a lot more that I could say about hydroids and other cnidarians. They really are among the most intriguing animals I've had the pleasure to observe, both in the field and in the lab. I've always been fascinated by their biphasic life cycle, with its implications for the animals' evolutionary past and ecological present. Perhaps I'll write about that some time, too.

1

A long time ago in a galaxy called the Milky Way, a great adventure took place. We don't know exactly when it happened, but it must have been very shortly after the evolution of the first cells. Some small prokaryotic cell walled itself off from its surroundings. Then it learned how to replicate itself and as cells continued to divide they began interacting with clones of themselves. Sooner or later, however, our clone of cells encountered cells from a different genetic lineage. These foreign cells were "other" and were recognized as such because they had a different set of markers on their outer covering. Perhaps there was an antagonistic interaction between the two clones of cells. In any case, this ability to distinguish between "self" and "non-self" was a crucial step in the evolution of life on Planet Earth.

The entire immune system in vertebrates is based on self/non-self recognition. It is why, for example, transplanted organs can be rejected by their new host--the host's immune system detects the transplanted tissue as "non-self" and attacks it. As a result, patients who receive donor organs usually take immune-suppressing drugs for some period of time after the transplant.

The vertebrate immune system is quite complex and very interesting. It has two main components: (1) cell-mediated immunity, in which the major players are T cells; and (2) humoral (i.e. blood-based) immunity, which is the part of the immune system that produces antibodies to a pathogen when you get a vaccination. However, even animals much less structurally complex than vertebrates have some ability to recognize self from non-self.

Sponges, for example, exist as aggregations of cells rather than bodies with discrete tissues and organs. Most zoologists, myself included, consider sponges to be among the most ancient animal forms. They have different types of cells, many of which retain the ability to move around the body and change from one type to another; this totipotency is a feature that sponge cells share with the stem cells of vertebrates. There are sponges that you can push through a mesh and disarticulate into individual cells, and then watch as the cells re-aggregate into an intact, functioning body. As if that weren't cool enough, if you take two different sponges and mush them into a common slurry, the cells from the distinct lineages re-aggregate with cells to which they are genetically identical. So even animals as primitive as sponges have some degree of self/non-self recognition.

If you're lucky, you can see self/non-self recognition and aggression in the intertidal. Here in northern California we have four species of sea anemones in the genus Anthopleura:

  • Anthopleura xanthogrammica, the giant green anemone
  • Anthopleura sola, the sunburst anemone
  • Anthopleura elegantissima, the cloning anemone
  • Anthopleura artemisia, the moonglow anemone (and my favorite)

Of these species, only A. elegantissima clones. It does so by binary fission, which means that the animals rip themselves in half.

Sea anemone (Anthopleura elegantissima) undergoing binary fission in a tidepool at Davenport Landing. 9 April 2016 © Allison J. Gong
Sea anemone (Anthopleura elegantissima) undergoing binary fission in a tidepool at Davenport Landing.
9 April 2016
© Allison J. Gong

It looks painful, doesn't it? As the two halves of the animal walk in opposite directions they pull apart until the tissue joining them stretches and eventually rips. Then each half heals the wound and carries on as if nothing had happened. Each anemone is now a physiologically and ecologically independent animal, and can go on to divide itself. And so on ad infinitum. The logical consequence of all this replication is a clone of genetically identical anemones spreading over a rocky surface. And that's exactly what you get:

Clones of the sea anemone Anthopleura elegantissima, emersed on a rock at Monastery Beach. 27 November 2015 © Allison J. Gong
Clones of the sea anemone Anthopleura elegantissima, emersed on a rock at Monastery Beach.
27 November 2015
© Allison J. Gong

Okay, it's hard to tell that these are sea anemones, but this is what they look like when the tide goes out and leaves them emersed. They pull in their tentacles, close off the oral disc, and cover themselves with sand grains. They look like sand but feel squishy and will squirt water if you step on them. In this photo, each anemone is probably 4-5 cm in diameter.

There are three patches of anemones in the photo above, separated by narrow strips of real estate where there are no anemones. Each patch is a clone, essentially a single genotype divided amongst many individual bodies. The anemones in each clone pack tightly together because they are all "self." However, they recognize the anemones of an adjacent patch as "non-self" and they won't tolerate the intrusion of neighbors onto their territory. Those strips of unoccupied (by anemones) rock are demilitarized zones. When the rock is submerged the anemones along the edges of the clones reach out their tentacles and sting their non-self neighbors. This mutual aggression maintains the DMZ and nobody gets to live there.

Because A. elegantissima lives relatively high in the intertidal the clonal patches are usually emersed when I go out to the tidepools. Its congener, A. sola, lives lower in the intertidal and is more often immersed at low tide. Anthopleura sola is larger than A. elegantissima and is aclonal, meaning that it does not divide. Anthopleura sola also displays quite dramatically what happens when anemones fight.

These two anemones, each about 12 cm in diameter, were living side-by-side in a tidepool. You can see that each animal has two kinds of tentacles: (1) the normal filiform feeding tentacles surrounding the oral disc; and (2) thicker, whitish club-shaped tentacles below the ring of feeding tentacles. These club-shaped tentacles are called acrorhagi, and are used only for fighting. The acrorhagi and the feeding tentacles may contain different types of stinging cells, reflecting their different functions. All tentacles are definitely not the same.

Anthopleura sola anemones fighting in a tidepool at Davenport Landing. 8 May 2016 © Allison J. Gong
Anthopleura sola anemones fighting in a tidepool at Davenport Landing.
8 May 2016
© Allison J. Gong

These animals, which represent different genotypes, are non-self to each other, so they fight. They inflate their acrorhagi, move their feeding tentacles out of the way, and reach across to sting each other. See how some of the acrorhagi on the animal on the right don't have nice smooth tips? Those tips have been lost during battle with the animal on the left; the tips are torn off and remain behind to continue stinging the offender even after the tentacle itself has been withdrawn.

Here's another picture of the same two anemones, taken from a different angle:

Anthopleura sola anemones fighting in a tidepool at Davenport Landing. 8 May 2016 © Allison J. Gong
Anthopleura sola anemones fighting in a tidepool at Davenport Landing.
8 May 2016
© Allison J. Gong

The goal of these fights is not to kill, but to drive the other away so that each anemone has its own space. Eventually one of them will retreat, and a more peaceful coexistence will be established. Fights like these have been going on for over half a billion years. Eat your heart out, George Lucas.

This morning I went out on the first morning low tide of the season. I was so excited to have the morning lows back that I got to the site early and had to wait for the sun to come up. Awesome thing #1 about early morning low tides: Having the intertidal to myself.

Dawn over Davenport Landing. 9 April 2016 © Allison J. Gong
Dawn over Davenport Landing.
9 April 2016
© Allison J. Gong

The purpose for the trip was to collect some algae for a talk I'm preparing; I'll be speaking to the docents at Natural Bridges State Beach at their monthly meeting this coming Wednesday. They invited me to talk to them about algae. I already have a lecture on algae prepared, but last year I set the bar pretty high with this particular audience and want do something a little different. So I'll talk to them for a bit, show them some of my pressings, and invite them to press a couple of specimens. This morning I collected a few pieces of algae and took a bunch of pictures.

The Anthopleura anemones continue to fascinate me. At Davenport Landing there's an area where the rock has eroded and forms a sort of channel. In this channel at low tide the water comes about up to my knees. The rock in the channel remains clear of algae but sometimes contains sand. Scattered over the bottom of this channel are several A. artemisia anemones, which can burrow into the sand when it is present. I've photographed these animals many times, as they are magnificently photogenic and in deep enough water that I can just stick my camera below the surface and click away.

This morning the first anemone I looked at in this channel had some orange gunk on its oral surface. At first I thought it had latched onto a piece of bleached algae, but then noticed that others had the same thing. My second thought was, "Ooh, eggs!" If I were at the lab I'd have sucked up some of the gunk and examined it under the microscope.

Spawning female Anthopleura artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning female Anthopleura artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong

Usually when animals spawn the gametes are quickly dispersed by water currents. But this channel is high enough that at low tide it doesn't exchange water with the ocean so there are no currents except those generated by the wind. Awesome thing #2 about early morning low tides: No wind. Once I used the camera as a sort of underwater microscope I could see the granular texture of the orange gunk, which told me that these were, indeed, eggs. Cool! Because I was on a hunt for algae I didn't spend a lot of time censusing these anemones, but I figured that statistically speaking they couldn't all be females. And sure enough, after a very short search I found some males.

Spawning male A. artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning male A. artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong
Spawning male A. artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning male A. artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong

So today I learned that April is when the A. artemisia anemones have sex. Makes sense, as spring is the time of year when many organisms (algae and invertebrates) in the intertidal reproduce. Reproduce sexually, that is.

Some animals reproduce clonally as well as sexually, and while sexual reproduction tends to be seasonal, clonal reproduction doesn't seem to be. Along the coast of central/northern California we have four species of anemones in the genus Anthopleura:

  • A. artemisia, the moonglow anemone (see above)
  • A. elegantissima, the aggregating anemone
  • A. sola, the sunburst anemone
  • A. xanthogrammica, the giant green anemone

Of these four species, only A. elegantissima clones readily. It does this by ripping its body in half in a process called binary fission. The two halves of the animal pull away from each other and the tissue between them gets stretched thinner and thinner until it rips. Then each former-half heals the wound and gets on with life, completely independent of the other. It sounds rather awful but is a very effective way to form clones of genetically identical units that can monopolize large areas in the intertidal.

Anemone (Anthopleura elegantissima) undergoing binary fission, at Davenport Landing. 9 April 2016 © Allison J. Gong
Anemone (Anthopleura elegantissima) undergoing binary fission, at Davenport Landing.
9 April 2016
© Allison J. Gong

It'll probably take this anemone another day or two to completely tear itself into two pieces. Anemones can continue to clone like this, with each individual splitting into a pair of individuals, for a long time. Eventually this process can form large clones. More about the ecology of these clones in a separate post some time.

While much of America was glued to the television watching a football game, I went out to the intertidal at Davenport Landing to do some collecting and escape from Super Bowl mania. The Seymour Center and I have a standing agreement that some animals--small hermit crabs and certain turban snails, for example--are always welcome, which gave me an excuse to look for them. I also needed to pick up some algae for labs that I'm teaching later this week, so it was an easy decision to be alone in nature for a couple of hours.

As usual, I was easily distracted by the animals, especially the anemones. They are simply the most photogenic animals in the rocky intertidal. And we have an abundance of beautiful anemones in our region; I feel very lucky to photograph them where they live. I would like to share them with you.

First up, Anthopleura sola:

Anthopleura sola 7 February 2016 © Allison J. Gong
Anthopleura sola specimen #1
7 February 2016
© Allison J. Gong
Anthopleura sola 7 February 2016 © Allison J. Gong
Anthopleura sola specimen #2
7 February 2016
© Allison J. Gong

Second species, Anthopleura xanthogrammica:

Anthopleura xanthogrammica 7 February 2016 © Allison J. Gong
Anthopleura xanthogrammica
7 February 2016
© Allison J. Gong
One large and one small Anthopleura xanthogrammica 7 February 2016 © Allison J. Gong
One large and one small Anthopleura xanthogrammica
7 February 2016
© Allison J. Gong

Along the central California coast we have four species of anemones in the genus Anthopleura. Two of them, A. xanthogrammica and A. sola, are large and solitary; in other words, they do not clone. The geographic ranges of these two species overlap in central California. Anthopleura xanthogrammica has a more northern distribution, from Alaska down to southern California, while A. sola typically lives from central California into Mexico.

I've seen these congeneric anemones living side-by-side in tidepools at Natural Bridges and at Davenport. Here is a photograph from yesterday. The animals are almost exactly the same size, and are separated by about 30 cm. Can you tell which is which?

So, which is which? 7 February 2016 © Allison J. Gong
So, which is which?
7 February 2016
© Allison J. Gong

The pièce de résistance yesterday was a treasure trove of Anthopleura artemisia anemones. I'd seen and photographed them several times before, and always appreciated the variety of colors they come in. For some reason, though, yesterday they really caught my eye. I had a number of "Wow!" moments.

Anthopleura artemisia specimen #1. 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #1.
7 February 2016
© Allison J. Gong
Anthopleura artemisia specimen #2 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #2
7 February 2016
© Allison J. Gong
Anthopleura artemisia specimen #3 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #3
7 February 2016
© Allison J. Gong

Sometimes two colors are combined:

Anthopleura artemisia specimen #4 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #4
7 February 2016
© Allison J. Gong

Stunning, isn't it?

But this next anemone is unlike any I've ever seen before. Get a load of this:

Anthopleura artemisia specimen #5 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #5
7 February 2016
© Allison J. Gong

These stark white tentacles are new to me. The anemone measured about 4 cm across. In every other aspect it looks like A. artemisia, and I'm almost entirely certain that's what it is. It does feel special to me. I will hopefully be able to keep an eye on this individual and see if its colorless tentacles are a temporary or long-term condition. And now that my eye has been primed to see the colors that A. artemisia comes in, I may notice more unusual color morphs.

1

So, those bits of Ectopleura crocea that I grabbed from the harbor on Monday are voracious eaters. I didn't feed them yesterday because I didn't have time and the students spent the afternoon looking at them in lab, and I hoped that they'd be alive today. Some of the stalks had dropped their hydranths (the distal part that bears the feeding tentacles, mouth, and reproductive gonophores) but most of them were alive and lovely. I had a nice fresh batch of brine shrimp all hatched out and ready to go and thought I'd see if the hydranths could eat them. Little did I know that this simple exercise would occupy most of my day.

I started by squirting some of the brine shrimp onto the hydranths, which for the most were pretty lackadaisical about catching them. Then I decided to feed them the mashed up brine shrimp that I'm still feeding the tiny Melibe and WOW! that did the trick! Maybe it was the scent of the macerated brine shrimp that triggered the feeding response. I was fascinated.

They are beautifully and unexpectedly animated animals.

After I watched them feed for a while, it seemed to me that the outer ring of tentacles catches and holds onto prey, while the prehensile manubrium swings around and brings the mouth into contact with the food. In the meantime, while all this brine shrimp catching is going on there are other larger crustaceans crawling all over the hydranths, even onto the tentacles, without getting stung. I think their exoskeletons must be thick enough not to be penetrated by the hydroid's cnidocytes (stinging cells).

Having discovered the trick to making the hydranths eat, I squirted brine shrimp mush on them and left them alone for about 20 minutes. When I came back they had eaten and I could see brine shrimp in their guts, so I gave them more. The feeding response was pretty much as vigorous as the first one had been. So I kept feeding them throughout the morning and early afternoon.

If I didn't have other things to do, I could watch these all day. I hope that if I can keep feeding them this much they will regrow their dropped hydranths. Although I'm not sure how realistic it is to think that I can go through this routine every day. And do I really need a few dozen more mouths to feed on a regular basis? I seem to accumulate animals like other women accumulate shoes. On the other hand, I don't expect the Ectopleura colonies to last long in the lab so even my "forever" relationship with these particular animals will likely be over in a week or so. I can probably keep up this level of effort for that long.

1

Tomorrow my students will be examining cnidarian diversity in lab, so early this morning I went to the harbor to collect hydroids. Or 'droids, as I refer to them. These are not the droids of Star Wars fame, such as C-3PO and R2D2, but rather colonial cnidarians. As such, they are made up of many iterated units (called zooids) connected by a shared gastrovascular cavity (GVC), or gut. Despite how weird it seems to most people, this sort of colonial lifestyle is not uncommon among marine invertebrates; it occurs in several other taxa as well, most notably the Anthozoa (sea amenones, corals, and others), Bryozoa (bryozoans such as Membranipora), and Urochordata (sea squirts).

On my various trips to the harbor over the past few months I've been keeping an eye out for 'droids, as I knew I'd need them. The one species I was glad to see getting established this summer is called Ectopleura crocea; it is one of the non-native members of the fouling community that shows up in harbors all along the California coast. It is a most beautiful animal, and quite conspicuous when it is present. This year I've seen it growing lustily on the docks, mussels, and any manmade object that has been marinating in the water for a while.

In situ it looks like this:

The hydroid Ectopleura crocea, at the Santa Cruz Yacht Harbor 19 October 2015 © Allison J. Gong
The hydroid Ectopleura crocea, at the Santa Cruz Yacht Harbor
19 October 2015
© Allison J. Gong

The stalks in this particular colony are 3.5-4 cm long. Each one of those tufts at the end of a stalk is a hydranth, the part of the zooid that bears the feeding tentacles and mouth. Hydroids are cnidarians and thus have stinging cells along their tentacles, which form a ring surrounding the mouth.

Ectopleura hydranths actually have two concentric rings of tentacles, with the mouth in the middle of the smaller ring. Between the tentacle rings there is a sort of empty space that is filled with reproductive structures called gonophores when the colony is preparing for sexual reproduction. In some hydroids gonophores release medusae, but in Ectopleura they release gametes. A given colony is either male or female, and any one of the hydranths can become reproductive and develop gonophores.

Hydroids are definitely animals whose beauty is better appreciated when observed under a microscope:

Hydranth of Ectopleura crocea 19 October 2015 © Allison J. Gong
Hydranth of Ectopleura crocea
19 October 2015
© Allison J. Gong

In the colonies of E. crocea that I've observed before, mature male gonophores are a solid white and female gonophores are pinkish. I collected three clumps of Ectopleura today, and none of the gonophores are mature. You can see why the common name for this animal is "pink mouth hydroid," as the mouth is borne on a pink tubular structure called a hypostome.

I've tried multiple times to grow this animal in the lab. There are some experiments on resource sharing in hydroids that I've been wanting to do for years but haven't yet found the right species to work with. In captivity Ectopleura eats well, then after several days all the hydranths drop off and the colonies die. I've never had success getting them to regrow their hydranths, either. So I bring them in for short periods and observe them up close while I can.

When I moved to the coast these many years ago and started poking around in the local intertidal, I became entranced with little animals called staurozoans. I can't claim to have been to every intertidal site in the area, but I've been to several of them and I personally know the staurozoans to occur at only two sites: Carmel Point (I've seen them there once) and Franklin Point (I used to see them there fairly regularly). In 2007 I went out to Franklin Point every month that had a negative low tide during daylight hours to monitor the abundance and size of the staurozoans; heck, once I even went out in the dark armed with a headlamp and a friend who was supposed to watch my back but instead fell asleep against the cliff. The staurozoans were easy to find that year and occurred in large numbers.

I used to be able to find the staurozoans in one particular area on the north side of Franklin Point where the water continually swashes back and forth.

Intertidal at Franklin Point, 3 July 2015. © Allison J. Gong
Intertidal at Franklin Point, 3 July 2015.
© Allison J. Gong

The staurozoans would always be attached to algae, often perfectly matching the color of their substrate. I remember seeing two versions, one a reddish brown and the other a vibrant bottle green color, of the same species of Haliclystus.

In March of this year I saw a lot of small staurozoans when I braved the afternoon winds at Franklin Point. The conditions were pretty horrid, with the water all churned up and murky so I couldn't take any pictures, but I was happy to see my little guys because it meant they were there. I hadn't seen them for a few years before this past spring and was beginning to doubt my search image. Huzzah for validating my gut feeling! I may have whooped and done the happy dance in my hip boots that afternoon.

Fast forward almost three months and three additional trips out to Franklin Point before I found a staurozoan this morning. One. And it was only about 0.5 cm tall, the same size that they were in March. And it was brown, the same color as most of the algae out there. Because they live where the water is constantly moving it's really hard to photograph them in situ. This is the best I could do:

Haliclystus sp. in situ at Franklin Point, 3 July 2015. © Allison J. Gong
Haliclystus sp. at Franklin Point, 3 July 2015.
© Allison J. Gong

It's hard to appreciate from this photo just how beautiful these animals are. They are very animated, swaying in the current and although they are attached they can slowly creep over surfaces or even detach, somersault around, and re-attach. Back in the day when I used to find them frequently I brought some back to the lab to observe them more closely. I could get them to feed, but they never lasted more than about a week in captivity.

So, what exactly are staurozoans? They are cnidarians, kin to sea anemones, hydroids, Velella velella, and jellies. Their common name is stalked jellies, and for a long time biologists considered them to be closely related to the jellies in the cnidarian class Scyphozoa. However, recent studies of the genetics of staurozoans have caused taxonomists to elevate these creatures to their own class, the Staurozoa.

Not much is known about the ecology of Haliclystus in California, probably because they are so damn difficult to find in the field. I have one or maybe two more trips out to Franklin Point this summer before we lose the minus tides for the season; hopefully they will still be there. I'd love to get some better pictures of them to show my students this fall. Wish me luck!

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