Skip to content

4

For some reason, many of the sunburst anemones (Anthopleura sola) in a certain area at Davenport Landing were geared up for a fight. I don't know what was going on before I got there yesterday morning, but something got these flowers all riled up. We think of them as being placid animals, but that's only because they operate at different time scales than we are used to. A paradox about cnidarians is that they don't do anything quickly except fire off their stinging cells; that, however, they do with the fastest known cellular mechanism in the animal kingdom. Go figure.

Pale green sea anemone with slender feeding tentacles surrounding the oral disc. Below the ring of feeding tentacles there is a ring of thick club-shaped tentacles used for fighting.
Sunburst anemone (Anthopleura sola) with inflated acrorhagi
2021-06-27
© Allison J. Gong

What looks like an anemone wearing a tutu is actually an anemone ready to fight. The normal filiform feeding tentacles are easily recognized. But those club-shaped white tentacles below the ring of feeding tentacles are called acrorhagi. They are all about fighting. The tips are loaded with potent cnidocytes that usually aren't used to catch food. They are used to fight off other anemones, and possibly predators.

Here's another shot of the same animal, which shows how the feeding tentacles and acrorhagi are arranged in concentric rings:

Pale green sea anemone with slender feeding tentacles surrounding the oral disc. Below the ring of feeding tentacles there is a ring of thick club-shaped tentacles used for fighting.
Sunburst anemone (Anthopleura sola) with inflated acrorhagi
2021-06-27
© Allison J. Gong

So who would this anemone be fighting? This individual was the only one of its kind in the pool where it lives. I don't know why its acrorhagi are inflated. I suppose they could be used to fend off a would-be predator, but I didn't see any other animal in the pool that seemed a likely candidate.

But look at this duo:

Two pale green sea anemones with slender feeding tentacles surrounding the oral disc.The anemone on the right has inflated fighting tentacles. The animal on the left has fewer inflated fighting tentacles.
Sunburst anemones (Anthopleura sola) with inflated acrorhagi
2021-06-27
© Allison J. Gong

Now, clearly there is (or had been) something going on between these individuals. They both have their acrorhagi inflated. I've been looking at this photo for a while and can't decide which is the aggressor. At first I assumed that the anemone on the right had initiated an attack on the other. But now I wonder if that is a defensive posture rather than an offensive one. That animal does seem to be more bent out of shape than the one on the left.

I've seen anemone fights before, and I've also seen anemones living side by side, tentacles touching, in apparently perfect amity. It's very clear that they can coexist peacefully. Why, then, do they sometimes choose to fight? It's important to point out that Anthopleura sola is an aclonal species. Unlike its congener A. elegantissima, whose primary mode of growth is cloning, each A. sola represents a unique genotype. With these anemones, whether or not two individuals fight is not determined by relatedness.

In a different pool these two anemones are sharing the carcass of a rock crab.

Sunburst anemones (Anthopleura sola)
2021-06-27
© Allison J. Gong

Maybe that third anemone at the top had also taken part in the feast, but at this point it seemed to be minding its own business. Given the demonstrated aggression of some A. sola, it would be interesting to know whether or not this trio ever fight amongst themselves. When we 'ooh' and 'aah' over them in the tidepools they look like passive flowers, and we forget that they are active predators. But we humans have access to the anemones' home for only a few hours every month, and I have no doubt that they get up to all sorts of shenanigans when we're not looking.

3

This morning I went to Natural Bridges. The tide this morning was the lowest of the season, but early enough that for the most part I had the intertidal to myself for a couple of hours. I always like those mornings best.

I did meet a docent out there, and we chatted for a few minutes. Towards the end of the excursion, when the tide had turned and I realized I had to get to the marine lab for the usual Friday feeding chores, she pointed out something that didn't make sense to her. She described it as two anemones side-by-side, but one was really stretched out down towards the water. She wondered what could be going on, as the other anemone looked normal.

Two large sea anemones at the edge of a tidepool. The anemone on the left is stretched down to more than twice the length of the anemone on the right.
Sunburst anemone (Anthopleura sola) and giant green anemones (Anthopleura xanthogrammica)
2021-06-25
© Allison J. Gong

Looks strange, doesn't it? What this anemone is doing, I think, is disgorging the remains of its most recent meal. If you look at the oral end, which is indeed stretched down towards the sandy bottom of the pool, you can see two things sticking out. The whitish blob is the internal part of the anemone's pharynx. It is not at all uncommon for anemones to sort of prolapse the pharynx, especially after a big meal. Remember, anemones have a two way gut with a single opening for both food ingestion and waste expulsion. The other thing sticking out of the mouth is a clump of mussel shells thickly coated with slime.

Here's a close-up of what's going on at the mouth of this anemone:

Sunburst anemone (Anthopleura sola) disgorging mussels
2021-06-25
© Allison J. Gong

It's hard to tell whether or not the mussels have been opened and digested by the anemone. It looks like at least some of the acorn barnacles attached to the mussel might still be alive, although smothered in slime. Nor can we see how many mussels are still inside the anemone's gut. In any case, the anemone is getting rid of this part of the mussel clump. However, this isn't a phenomenon that can really be watched, unless you can watch in time-lapse. The docent asked, "Doesn't it use peristalsis, or something like that?" The answer is that no, anemones don't use peristalsis. They don't have the type of muscles that can contract in that way. The anemone still has to somehow expel wastes and undigestible matter from its gut, through that single opening that we call a mouth but functions as both mouth and anus.

Our human gut, of course, uses peristalsis to move food along from esophagus to rectum. And while for the most part we don't like to think about how that works, we have all experienced what happens when things don't go as planned. I doubt that anybody gets through life without vomiting, so it is probably safe to say we all know that it is a violent way to thoroughly expel food, toxins, and other noxious items from the stomach. Anemones, however, have no peristalsis and cannot vomit. How, then, does an anemone void its gut of something larger than the typical digestive waste?

This particular anemone is ideally situated to let gravity do the work. Hanging down like this and relaxing the simple sphincter muscle around the base of the tentacles will allow the mussel clump to eventually fall out. Without peristalsis to speed things along, it will probably take a while. Would it be finished by the time the tide comes back? I couldn't stick around to watch, so I can't say. But it was a very cool thing to see, even though it happens about as fast as paint drying.

1

In Morro Bay, CA, there is a stand of eucalyptus trees that has been designated a natural preserve. In 1973 the Heron Rookery Natural Preserve was established to protect great blue herons (Ardea herodias) as they nested. Since then other bird species have taken to nesting in these same trees. When we were there at the end of May we saw these species with nests in the eucalyptus trees:

  • Great blue heron (Ardea herodias)
  • Double-crested cormorant (Phalacrocorax auritus)
  • Great egret (Ardea alba)
  • Snowy egret (Egretta thula)

This particular rookery is not at all removed from human activity. It is right across the street from the municipal golf course and next to a hotel, and there is a walking/biking trail that runs directly under the trees. Signs advise people to keep their voices down, but pedestrians are walking under the trees all day, dodging the rainfall of guano from above. The birds don't seem to be bothered.

Unlike the Brandt's cormorants (Phalacrocorax penicillatus), which nest on cliffs and rocks, the double-crested cormorants nest in trees. Birds build nests with local materials, and there is a difference in what I could see making up the nests of these two species. The Brandt's cormorants at Natural Bridges in Santa Cruz were using seaweeds as the main building material; I could see birds flying back with algae in their beaks, and then either handing it off to a mate on the nest or tucking it into the existing structure itself. In some cases I could see the pieces of algae well enough to make a tentative ID.

Group of ~40 large black marine birds on a rock. ~12 nests of mounded algae, with a single bird lying on it. Other birds standing on rock, preening or presenting algae to their mate. Some birds show blue throats of breeding plumage.
Brandt's cormorants (Phalacrocorax penicillatus) nesting on rock arch at Natural Bridges
2021-05-14
© Allison J. Gong

Those are the Brandt's cormorants. The double-crested cormorants nest in the trees, as we saw at the heron rookery. Here's a pair that have a brood of three chicks:

Family of large black seabirds in a eucalyptus tree. The nest contains three chicks and one parent. The other parent is perched on a nearby branch.
Double-crested cormorant (Phalacrocorax auritus) parents and trio of chicks
2021-05-23
© Allison J. Gong

At Morro Bay, which is an estuary rather than a rocky area, the double-crested cormorants use a lot of eelgrass (Zostera marina) in their nests. Eelgrass is very abundant in the Morro Bay harbor and Estero, whereas the birds would have to fly a bit farther to gather algae. Eelgrass, being a true plant, is less slimy than the algae are, and these cormorants' nests look much drier than the mounds of algae used by the Brandt's cormorants up in Santa Cruz.

A short distance up the coast at San Simeon the double-crested cormorants were nesting in a smaller rookery, also in eucalyptus trees. I liked the pattern of how these four nests were situated in three-dimensional space:

Four nests in a dead eucalyptus tree. There is one adult black cormorant in each nest.
Double-crested cormorants (Phalacrocorax auritus) nesting at San Simeon
2021-05-23
@ Allison J. Gong

Returning to goings-on at the heron rookery in Morro Bay, the herons and egrets were also raising youngsters in that stand of eucalyptus trees. Remember, this rookery is very easily visited by humans. Here's a view of the trees, taken from the small parking area:

Grove of eucalyptus trees
Heron Rookery Natural Preserve in Morro Bay, California
2021-05-23
© Allison J. Gong

It's difficult to photograph the nests because of all the branches obscuring the view. We were also there near mid-day, with the overhead sun making lighting conditions less than favorable for good photography. I did find one comparatively visible heron nest, containing one parent and one sullen punk-ass teenager of a chick. The nestling had started growing feathers but was still almost half fluff, clearly not ready to fly yet.

Large gray-ish blue bird and its partially-feathered chick in their nest in a eucalyptus tree.
Great blue heron (Ardea herodias) nest at the Heron Rookery Natural Preserve
2021-05-23
© Allison J. Gong

Both great egrets (Ardea alba) and snowy egrets (Egretta thula) nest at the heron rookery. Here's a great egret nest with two chicks:

Large white bird with two white chicks in a nest in a eucalyptus tree
Great egret (Ardea alba) nest at the Heron Rookery Natural Preserve
2021-05-23
© Allison J. Gong

From what I could see, the herons and egrets don't use any marine material at all to build their nests. One factor that determines the suitability of a potential building material is proximity—even if a certain material is fantastic in other ways, birds may not use it (or may use less of it, compared to other materials) if it costs too much energy to fetch and bring back to the nesting site. For the herons at this site, sticks are easy to come by. Another thing to consider is that herons and egrets are not marine birds. Although some populations live and nest in coastal areas, most do not. Thus it is not surprising that their nests are built from materials that are terrestrial rather than marine.

I did not see any snowy egret nests in areas where they could be photographed well. However, there were some adult snowies in their spectacular breeding plumage. There was enough of a breeze to ruffle up those long plumes that used to be harvested to decorate ladies' hats.

Look at these beautiful birds!

White bird with long black legs and a black beak perched in a eucalyptus tree. Long white plumes blow away from the birds head, neck, and back.
Adult snowy egret (Egretta thula) in breeding plumage
2021-05-23
© Allison J. Gong
White bird with long black legs and a black beak perched in a eucalyptus tree. Long white plumes blow away from the birds head, neck, and back.
Adult snowy egret (Egretta thula) in breeding plumage
2021-05-23
© Allison J. Gong

For several decades now, the cormorants, herons, and egrets have been nesting in these eucalyptus trees, which brings to mind the consideration of native versus non-native species. The trees themselves, blue gum eucalyptus (Eucalyptus globulus) are non-native, having been imported to California from Australia starting in the 1870s. This introduction was encouraged by calls to replace native trees that had been cleared for fuel and building material, both of which were desperately needed during and after the Gold Rush. Since ecologists began considering the effects of non-native species in the 1980s there has been a backlash against the blue gums. Given their large size, their having been planted in groups to serve as windbreaks, and their propensity for dropping a lot of debris, they are very conspicuous, and it is easy to get all hot and bothered at how in certain places they dominate the landscape.

Great egret (Ardea alba) in flight
2021-05-23
© Allison J. Gong

At which point, however, does a species cease to be considered non-native? Having been established in California for 150 years, what is the role of E. globulus in the ecology of the Golden State? There are many people and organizations that would like to see the blue gums eradicated, or at least their populations greatly reduced. On the other side of the argument, groups such the San Francisco Forest Alliance posit that blue gums should be treasured as heritage trees.

At the Heron Rookery, some of the eucalyptus trees are dying. One reason is sheer old age. Another is the several decades' accumulation of bird wastes onto the soil, which is slowly killing the trees. As the blue gums die, the birds will have to find other places to nest. One of the pro-eucalyptus arguments is that many species of native birds—not just these here but other species such as red-tailed hawks, red-shouldered hawks, and a whole host of songbirds—nest in eucalyptus trees throughout the state. If the blue gums are removed, then where will these undoubtedly native birds nest? Especially if the native trees have long been gone?

Taking the long view, my guess is that the birds will figure it out. Ecological communities evolve over thousands of years. The 150 years of the eucalyptus trees' presence in California seems like a long time, but in terms of ecological time they are merely a blink of the eye. The herons, egrets, and cormorants have been nesting at the Heron Rookery for an even shorter period of time. When this stand of blue gums is gone, due to either natural attrition or removal by humans, the birds will find another place to nest. They might not choose a place that is so easily visited and observed by people, though.

%d bloggers like this: