Summer photos 6: a snail's trail

L. littorea, spotted in May.

One more photo from that May collecting trip. Here's a periwinkle off its more frequent rocky habitat, motoring across a bit of sand. As fast as a snail can motor, anyway.

Summer photos 5: intertidal zonation

This post has actually been in my brain for a while. When I was on a collecting trip in May (yes, we're still in May in my picture review), I noticed this on a boulder:

Spotted in the Rhode Island intertidal. The light tan stuff on the tops of the rocks are barnacles. The black clumpy stuff on the bottoms are mussels.

 Looking more closely, you can see these two animals more clearly:

Barnacles (Semibalanus balanoides, probably) and mussels (Mytilus edulis) coexisting on a rock. Note that the barnacles are growing on some of the mussels. If you look carefully, you can spot several periwinkles (introduced in this post) crawling around this habitat.

This is one of the few times that I'm out in the field and really see a textbook example of an important ecological process. What's going on here is called zonation, and it is arguable one of the most important processes in marine communities. It's also a great example of critical experimental work and leads to two of the most influential marine ecologists of all time.

But to back it up a bit, we now have an observation: mussels live lower than barnacles on the shore, and the division between them is often very sharp. It happens that this observation is repeated all over the world on rocky shores.

Zonation on a rocky shore in Washington. The photo's from Wikipedia, and the zones are a little harder to see, but they're there. Also note that in this photo you can see a band of orange and purple sea stars.

Ok, so as scientists we want to know what is causing this pattern that we observe. And this brings me to Joseph Connell and Bob Paine, two ecologists who were crucial in bringing experimentation to the discipline of ecology and changed the way we as marine ecologists do science.

Working in Scotland in the 1950s, Connell designed a series of very elegant experiments with two species of barnacles to show why one lived higher in the intertidal zone than the other, and why they were limited at the lower end of the intertidal zone. To explain the experiment fully takes a whole class period for our marine ecology students, but here is a brief summary of the salient points for these photos:

1. Barnacles dry out if they are exposed to the air and sun for too long (i.e. out of the water too long at low tide). This limits how high they live on the shore.
2. Barnacle predators live lower in the intertidal because they are more sensitive to dessication and heat stress. This means that the barnacles are limited at the lower end of the intertidal zone by a high density of things that eat them.

Paine's experiments were done on a remote island in Washington (Tatoosh Island) in the 1960s. He was interested in the lower limit of the mussel band in the intertidal zone. By going out and removing all of the sea stars (the main predator of the mussels) in his experimental plots, he showed that mussels could grow lower in the intertidal zone in the absence of their predators. To flip that around, their distribution was limited by their survival in the face of predation. But removing the predators did more than extend the mussel zone: it also allowed the mussels to outcompete all other invertebrates in that zone (especially barnacles), leaving a monoculture of mussels. That is, the mussels outcompete the barnacles. BUT, the mussels have a lower dessication tolerance than the barnacles, so they can't get as high on the rocks.

To put all of this together, barnacles are most tolerant of being out of the water, which is why they can live on the tops of those boulders in the first photo. But the mussels can outcompete them lower in the intertidal zone, so there is a sharp division between mussels and barnacles that presumably corresponds to microclimatic conditions on the rocks. There's not many sea stars in the Rhode Island area I was visiting, but if there were they should exist even lower on the shore than the mussels.

So there you have it: one of the most important stories in marine ecology to explain one of the most pervasive patterns on rocky coasts around the world.

See how jagged the lines are here? That probably relates to either variation in microclimate (i.e. warmer / cooler places on the rocks) or potentially disturbance events. I'd have to take temperature measurements to know.

Summer photos 4 and a link

Nucella lapilus, a dogwhelk, on a rock covered in barnacles.

I'm still working through the photos from my late-May collecting trip. This is Nucella lapilus, a carnivorous snail that is very common on the Atlantic coast. This particular one is white, but elsewhere on the coast you can see them in many different colors.

In fact, here's some from New Jersey from a previous year:

Different color morphs of N. lapilus on a rock. There's a white one, several dark ones, and a couple of orange ones. Also note that they are smaller than the guy from further north on the coast. That's a pretty common pattern in ectothermic things (they get larger in colder environments).

I also would be remiss if I didn't tell you to go read the wonderful post from the Collin lab blog about sex ID in Crepidula species: how to ID male and female snails and why it matters.

Summer photos: 3

Littorina littorea, the common periwinkle.

This little guy was spotted while tidepooling in Rhode Island in May. It's a nice specimen of Littorina littorea, the common periwinkle, and you can see several others in the background. This is a large, herbivorous snail that is common on rocky or cobble shores in this part of the world. You can see the small rockweed (Fucus sp.) shoots in the photo trying to make a go of it, and the rock is covered with barnacles. This is pretty typical for around here.

L. littorea is an introduced species on this coast of North America; it came over from Europe in the mid-19th century and has since spread far from its introduction site in the northeast. In their native range, they are an important food source (I've seen them served at a seaside bar in northwest France), but aren't widely consumed here.

Summer photos: 2

Shells on the beach at the ferry terminal, May. In the center is a razor clam shell, with a Crepidula stack to the right. Razor clams live buried in the sand, but I frequently find their empty shells washed up on the beach.

Leaving on a collecting trip, May. Some days my job is pretty great.

Summer photos: 1

I have a backlog of photos from collecting trips that I have been meaning to post and talk about. This month seems like a good time to do it, while I'm madly trying to finish experiments before school starts again (and simultaneously preparing for the fall semester). Few words, many pictures.

From a May collecting trip:

Fucus sp., a brown alga (rockweed), covered with the egg capsules of Ilyanassa obseleta, the mud snail. Each egg capsule is filled with developing embryos that will hatch into planktonic veligers.

A moon snail egg case (the sand collar) also covered with I. obsoleta egg capsules.

Internet quiz and scyphozoan medusa -- all in a day's work

I've scuttled off to points north to find snails. It's been a delightful trip, but I'm not done, won't be back for a while, don't want to write about the experiment I threw in the field before I got back (not literally threw, but close), so instead, here is a fun marine inverts memory quiz to play with. Play several times, there's some new animals each time.

A jellyfish washed up on the beach. I successfully avoided getting stung today, despite the fact that there were dozens in the water and on the beach and I wasn't paying the least bit of attention to them (too busy snail-hunting).

Marine invert sighting of the week

ETA: Thanks to the wonders of social networking, the ID of the worm is now in question. Without the animal I don't want to say anything for sure, but it may in fact be from a different polychaete annelid family (Onuphidae).

The title of this post is actually a misnomer, because I never saw the animal in question. I was collecting snails at a new location yesterday. The beach looked like this:

Beach covered with worm tubes.

The silty sand was being held together by dozens of large tubes. Tubes on a beach are not new to me. Many polychaete worms (distant relatives of the familar earthworm) make tubes out of sand or other materials on the beach. These animals live in their tubes, pumping food and oxygen down into the sediment to well below the level where such resources are normally found. The tubes also add structure to an otherwise unstructured area, and can change erosion and other dynamics of the beach quite drastically.

Normally the tubes I see are small, just a couple of centimeters above the sand. These were big honking tubes, made of a parchmenty substance with lots of pebbles and bits of shell attached.

Worm tube, with hand for scale.

It took me a little while, but eventually I realized that these tubes must belong to a group of worms that we showed our students in Invertebrate Zoology this year. I didn't have a shovel, so I wasn't able to uncover these massive tubes and check for sure. But I was in the right area, and the tubes look right, so I'm confident that I can claim to have seen this guy:

Chaetopterus spp. Photo from Wikipedia.

 Man, these worms are bizarre looking, are they not? The head end is at the top in the photo above. Each of the different segments has evolved to specialize on a different task. Some pump water through the burrow, some aid in various parts of the feeding of the organism (they feed using a mucus net to filter particles from the water).

For me, invert-lover that I am, it was very exciting to find and identify a specimen that I had previously only seen in the classroom. Plus, I found what I need for my research, so it was a good morning all around.

Cycles, vacation, and my brief absence

My job is very cyclical. As previously discussed, I am heavily dependent on the tides to determine when I need to go out in the field and get animals for my work. There really isn't much leeway in when the tides will be good, which means that for at least one week out of the month, I have to plan to do as much collecting work as possible (especially in the summer). It also means that when I get up on a collecting morning and it is too early or rainy or unbearably hot or there might be too much traffic because of a holiday weekend, I don't really get to go back to sleep.

On top of that is added the reproductive cycle of the snails. I am lucky in that Crepidula reproduce for a very large window of time, at least in my location. I can reliably find field-collected larvae to work with from April/May until October. This is in sharp contrast with, say, coral reproduction, which is frequently centered on just a single night of the year (and woe betide the researcher who misses that night). Perhaps a post on synchrony in corals is something I will do in the future.

Still, despite this thankfully broad window to work with, I find myself running around doing half-a-dozen different experiments every summer, trying to capitalize on the field season as much as possible. And, of course, the academic calendar does not line up perfectly with the animals, meaning that in both spring and fall there is a painful period where I am doing both my academic and my field work.

None of that is to justify why it has been a month since I posted, though. It turns out that the last couple weeks looked something like this:

One of my field sites, mid-June, while I was deploying an experiment.

Snowbird, Utah, site of the 2013 Evolution meeting, taken < 24 hours after the previous picture.

Zion National Park, Utah.

Yes, I took a glorious week off to go west (don't panic, I had an experiment running itself while I was away). Both the scientific meeting and the brief vacation afterwards were glorious, but mostly invertebrate-free. Actually, that's a complete lie, since we saw many beautiful insects in both the mountains and the deserts, but no marine invertebrates. I was disappointed not to see a tarantula or scorpion in the desert, but that's pretty easy to say from the comfort of my couch. And there were no snails spotted in the mountains, though I did see a single freshwater snail in a reservoir near Zion.

When I returned to the humid Northeast, I found my snails in good condition, so I'm getting painfully back to the grind, trying to get as much done as I can before the academic year cycles back around again.

The birds, the bees, and the snails in my lab

Mating Crepidula fornicata. Photo credit A. Cahill

It's summer. I can tell because I'm working crazy hours again and loving almost every minute of it.

Last Saturday night, around midnight, I was feeding the snails in the lab when I found a mating stack, something I've never seen before. The female had become detached from her substrate, which is why I could see what was going on. She's the bottommost snail on the stack below, with her head towards the right of the shell. Normally she would be holding on to the side of the tank with her large, muscular foot.

You can see two males trying to inseminate her in this photo. The one on the right is the male closest to her in the stack, and he was actively mating at the time. I could tell because the male on the left (second from the female in the stack) withdrew into his shell when I disturbed the water, but the other guy carried on as if nothing was the matter.

The next morning I came back in and the closer male had finished and withdrawn, but the other male was now actively mating with the female. Then I flipped the stack over so the female would be able to reattach to the tank and survive, so I don't know how the drama ended.

Female C. fornicata can store sperm from multiple matings for many months (probably over a year). The eggs that are ultimately laid by this female will have been fertilized by several males -- maybe even all of the males in her stack. And then I will have more larvae to study, and the circle of life work continues on.