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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.

Every year, as early as Memorial Day or as late as Father's Day, there's about a week of really lovely low tides. This midsummer tide series usually includes the lowest low tides of the year, and we intertidal ecologists plan our field activities around them. Incidentally, there's a corresponding low tide series in the midwinter, too. However, at that time of year the lows are in the afternoon, and because the low occurs about 50 minutes later each day you're fighting darkness as you work the series. But in the summer, even if the first day of the tide series has a low tide before sunrise, that 50-minutes-later-each-day thing is really nice and you never have to worry about running out of daylight.

This year, the California Academy of Sciences sponsored several citizen science excursions called Bioblitzes to various locations on the California coast. The goal of these Bioblitzes was to document biodiversity in the intertidal in protected and non-protected areas of the coastline. Back in May I volunteered to lead a Bioblitz at one of the sites close to me, and planned to participate in a few others as well. In addition to actual organized Bioblitzes, citizens were invited to submit their own independent observations to the project.

Today is the three-week anniversary of the car accident that left me bruised and concussed. The bruises are pretty much healed at this point, and the soreness in my ribcage is also much improved. The medical advice I got for dealing with the concussion was, "Protect your brain from stimulation. Let it heal. And REST." So for the past three weeks I haven't been doing much of anything. I was worried that I wouldn't be able to go out on any of the midsummer low tides, as it didn't take much to overtax my injured brain and I didn't want to risk overextending myself. I did end up skipping the first Bioblitz of the week and modified my original plans for the rest of the tide series to play it safe and stay closer to home.

I'm still trying not to spend too much time on the computer (electronic screens are very bad for injured brains) so I'm going to summarize my week's activities in a single post. I'll keep the stories short. But I did want to share some of the things I saw.

Day 1 - Natural Bridges, Monday 6 June 2016, low tide -1.6 ft at 06:25

My first venture out by myself was to Natural Bridges. It's very close to my house and I figured that if I needed to bail I could walk out and be home within 15 minutes. It was cold and foggy and I felt energized just to be out there again.

Natural Bridges State Beach 6 June 2016 © Allison J. Gong
Natural Bridges State Beach
6 June 2016
© Allison J. Gong
Open ends of tubes of the polychaete worm Phragmatopoma californica. 6 June 2016 © Allison J. Gong
Open ends of tubes of the polychaete worm Phragmatopoma californica.
6 June 2016
© Allison J. Gong
Anthopleura sola in a tidepool at Natural Bridges. 6 June 2016 © Allison J. Gong
Anthopleura sola in a tidepool at Natural Bridges.
6 June 2016
© Allison J. Gong
One of many healthy Pisaster ochraceus stars I saw at Natural Bridges. 6 June 2016 © Allison J. Gong
One of many healthy Pisaster ochraceus stars I saw at Natural Bridges.
6 June 2016
© Allison J. Gong
Intertidal life at Natural Bridges. 6 June 2016 © Allison J. Gong
Intertidal life at Natural Bridges.
6 June 2016
© Allison J. Gong
A woolly sculpin (Clinocottus analis) in a tidepool at Natural Bridges. 6 June 2016 © Allison J. Gong
A woolly sculpin (Clinocottus analis) in a tidepool at Natural Bridges.
6 June 2016
© Allison J. Gong
Shore crab (Pachygrapsus crassipes) playing peek-a-boo at Natural Bridges. 6 June 2016 © Allison J. Gong
Shore crab (Pachygrapsus crassipes) playing peek-a-boo at Natural Bridges.
6 June 2016
© Allison J. Gong

Turns out this trip was about all my brain could cope with that early in the week. I skipped a Bioblitz up at Pigeon Point on Tuesday so I could stay home and rest, which ended up being a good call. A whole day of doing nothing was exactly what my concussed brain needed.


Day 2 - Mitchell's Cove, Wednesday 8 June 2016, low tide -1.1 ft at 08:02

The day of rest was enough to get me back out there on Wednesday. My friend Brenna met me at Mitchell's Cove for a morning of tidepooling. Mitchell's Cove is a popular, dog-friendly beach in Santa Cruz, particularly busy in the mornings and evenings. Last September it was visited by a juvenile humpback whale, which came right into the Cove and hung out there for several days. I didn't see any whales this week, but there was a surprising diversity of life in a relatively small area of rocky intertidal.

Rocky intertidal on the west end of Mitchell's Cove. 8 June 2016 © Allison J. Gong
Rocky intertidal on the west end of Mitchell's Cove.
8 June 2016
© Allison J. Gong
Pisaster ochraceus regenerating an arm, at Mitchell's Cove. 8 June 2016 © Allison J. Gong
Pisaster ochraceus regenerating an arm, at Mitchell's Cove.
8 June 2016
© Allison J. Gong
A small (~2 cm long) chiton, Mopalia muscosa, nicely camouflaged on a rock at Mitchell's Cove. 8 June 2016 © Allison J. Gong
A small (~3 cm long) mossy chiton, Mopalia muscosa, nicely camouflaged on a rock at Mitchell's Cove.
8 June 2016
© Allison J. Gong

We have two species of surfgrass in northern California. At this time of year they are very lush and conspicuously green.

Two species of surfgrass at Mitchell's Cove. Phyllospadix torreyi (front) and P. scouleri (rear). 8 June 2016 © Allison J. Gong
Two species of surfgrass at Mitchell's Cove. Phyllospadix torreyi (front) and P. scouleri (rear).
8 June 2016
© Allison J. Gong

Phyllospadix scouleri, the species that has flatter, more ribbon-like leaves, was blooming. Its congener, P. torreyi, growing in almost exactly the same place, has narrow leaves that are more cylindrical in cross-section, and was not in bloom. Phyllospadix is a true marine plant; the flowers are inconspicuous swellings near the bottom of the leaves and the pollen is carried by water, rather than wind, to nearby plants.

Surfgrass (Phyllospadix scouleri) in bloom at Mitchell's Cove. 8 June 2016 © Allison J. Gong
Surfgrass (Phyllospadix scouleri) in bloom at Mitchell's Cove.
8 June 2016
© Allison J. Gong
Flower of surfgrass Phyllospadix scouleri at Mitchell's Cove. 8 June 2016 © Allison J. Gong
Flower of surfgrass Phyllospadix scouleri at Mitchell's Cove.
8 June 2016
© Allison J. Gong

And I saw two species of hydroids! This one is easy to ID to the genus Aglaophenia, but I would need to examine it under a microscope to determine the species. I wasn't collecting anything on Wednesday so I don't know which species it is.

Hydroid (Aglaophenia sp.) at Mitchell's Cove. 8 June 2016 © Allison J. Gong
Hydroid (Aglaophenia sp.) at Mitchell's Cove.
8 June 2016
© Allison J. Gong

This second hydroid is, I think, a species of Abietinaria. The hydroid colony is the pale orange stuff; the pink stuff is coralline alga.

Small clump of the hydroid Abietinaria sp. at Mitchell's Cove. 8 June 2016 © Allison J. Gong
Small clump of the hydroid Abietinaria sp. at Mitchell's Cove.
8 June 2016
© Allison J. Gong

And I saw an octopus! We know that they're in the intertidal, but they are so cryptic and clever at hiding that we don't see them very frequently. This one was definitely smarter than I was. Instead of scooping it out and placing it on dry ground so I could photograph it more easily, I chased it around a tidepool with my camera. Thus, this is the best picture I could get:

Small octopus (Octopus rubescens) in a tidepool at Mitchell's Cove. 8 June 2016 © Allison J. Gong
Small octopus (Octopus rubescens) in a tidepool at Mitchell's Cove.
8 June 2016
© Allison J. Gong

Okay, you'll just have to take my word for it.


Day 3 - Davenport Landing, Thursday 9 June 2016, low tide -0.7 ft at 08:52

This was the day of my "official" Bioblitz. I had four participants--Brenna, Alice, Martha, and Andy. As of right now (Brenna hasn't yet uploaded her observations) the other four of us have made 120 observations, documenting 50 species. Here are some of mine:

Nudibranch (Hermissenda opalescens) at Davenport Landing. 9 June 2016 © Allison J. Gong
Nudibranch (Hermissenda opalescens) at Davenport Landing.
9 June 2016
© Allison J. Gong
Can you see Pisaster ochraceus hiding in this clump of mussels (Mytilus californianus)? 9 June 2016 © Allison J. Gong
Can you see Pisaster ochraceus hiding in this clump of mussels (Mytilus californianus)?
9 June 2016
© Allison J. Gong
Looking north towards Davenport Landing beach. 9 June 2016 © Allison J. Gong
Looking north towards Davenport Landing beach.
9 June 2016
© Allison J. Gong

There are kelps, such as Egregia menziesii (feather boa kelp) whose habitat is the rocky intertidal. Most kelps, though, live subtidally, often in kelp forests. Nereocystis luetkeana, the bullwhip kelp, is one of the subtidal canopy-forming kelps. This one recruited to the intertidal. It is quite small and extremely cute; the float is only 2 cm in diameter.

A baby bullwhip kelp (Nereocystis luetkeana) at Davenport Landing. 9 June 2016 © Allison J. Gong
A baby bullwhip kelp (Nereocystis luetkeana) at Davenport Landing.
9 June 2016
© Allison J. Gong
A small moonglow anemone (Anthopleura artemisia) at Davenport Landing. 9 June 2016 © Allison J. Gong
A small moonglow anemone (Anthopleura artemisia) at Davenport Landing.
9 June 2016
© Allison J. Gong

Algae look their best when immersed. Out of the water they usually collapse into stringy or gooey masses, making it difficult to appreciate their structural beauty. This piece of Microcladia borealis was submerged in a tidepool, and fortunately there was enough light that I could take this picture.

The beautifully delicate red alga, Microcladia borealis, at Davenport Landing. 9 June 2016 © Allison J. Gong
The beautifully delicate red alga, Microcladia borealis, immersed in a tidepool at Davenport Landing.
9 June 2016
© Allison J. Gong

Day 4 - Natural Bridges, Friday 10 June 2016, low tide -0.2 ft at 09:42

Yesterday I returned with a former student, Daniel, to Natural Bridges. It was sunny and warm, completely different from how it had been on Monday. There were many boaters out on the bay, taking advantage of the glassy flat sea.

View of Monterey Bay from Natural Bridges. 10 June 2016 © Allison J. Gong
View of Monterey Bay from Natural Bridges.
10 June 2016
© Allison J. Gong

I've seen a lot of shore crabs running around on the rocks this year. On cool, damp days they just scurry about, but on warm sunny days they often sit still and literally foam at the mouth. The bubbles they produce keep their gills moist so they can still breathe even while emersed. This biggish shore crab was working up quite a froth.

Shore crab (Pachygrapsus crassipes) at Natural Bridges. 10 June 2016 © Allison J. Gong
Shore crab (Pachygrapsus crassipes) at Natural Bridges.
10 June 2016
© Allison J. Gong

Hermit crabs don't usually end up out of the water. This one was immersed in a tidepool, wearing the shell of the snail Olivella biplicata.

Hermit crab (Pagurus sp.) in shell of the snail Olivella biplicata, at Natural Bridges. 10 June 2016 © Allison J. Gong
Hermit crab (Pagurus sp.) in a tidepool at Natural Bridges.
10 June 2016
© Allison J. Gong

Nuttallina californica is one of the most common chitons seen around here. They often hunker down into small crevices where water will collect even at low tide. This individual was nestled among a clump of Phragmatopoma tubes; being closely surrounded by other animals will help keep its own body moist.

Nuttallina californica, one of the most common chitons at Natural Bridges. 10 June 2016 © Allison J. Gong
The chiton Nuttallina californica at Natural Bridges.
10 June 2016
© Allison J. Gong

Unlike the hard granite that you'd find at the southern end of Monterey Bay, the rock at Natural Bridges is a soft, easily eroded mudstone. You can scratch it with your fingernail. Limpets take advantage of this soft rock by digging themselves little home scars, which conform perfectly to the contours of their shells and make a snug, water-tight fit. The limpet leaves its home scar to forage when the tide is in and returns to it as the tide recedes. The owner/occupant of this scar has likely died, as it wouldn't have abandoned its home scar when we were there at low tide.

Home scar of a limpet (Lottia sp.) at Natural Bridges. 10 June 2016 © Allison J. Gong
Home scar of a limpet (Lottia sp.) at Natural Bridges.
10 June 2016
© Allison J. Gong

And speaking of limpets, Daniel and I spent a lot of time observing the owl limpet, Lottia gigantea. This limpet is noteworthy not only for its large size, but for its territorial behaviors. They are indeed large--the biggest ones I've ever seen are about the size of the palm of my hand--and the big ones are all females. Lottia gigantea is a protandrous hermaphrodite: individuals begin sexual maturity first as males, and then the lucky few turn into females.

Owl limpet (Lottia gigantea) at Natural Bridges. 10 June 2016 © Allison J. Gong
Owl limpet (Lottia gigantea) wearing a smaller limpet (Lottia sp.) at Natural Bridges.
10 June 2016
© Allison J. Gong

The truly remarkable thing about L. gigantea is its ability to modify the environment. The large females maintain an area called a farm, from which they diligently remove interlopers. They will scrape off settling larvae of barnacles and mussels, and will push off other limpets. Lottia farms are very common at Natural Bridges; if you are here and see a suspiciously empty patch of rock amid the mussel bed, look for a big limpet hanging out on the edge of the empty spot.

Farm of an owl limpet (Lottia gigantea) at Natural Bridges. 10 June 2016 © Allison J. Gong
Farm of an owl limpet (Lottia gigantea) at Natural Bridges.
10 June 2016
© Allison J. Gong

The owl limpet has a good reason for keeping other animals off her territory. It provides her food. This animal is indeed a farmer. See the pale zig-zag markings in the Lottia farm? Those are marks made by the limpet's radula as she grazes over the rock. All limpets are grazers, but L. gigantea actively manages her farm so that she feeds on one area while allowing the algal film to grow on other areas, then rotates to a new feeding spot as the old one becomes depleted. Pretty clever for a snail, isn't it?

It felt really good to spend some quality time with Mother Nature again. I'm still taking it very easy, careful not to get overtired and to continue letting my brain heal. Getting outside for even short periods definitely seems to help.

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