Friday, August 23, 2013

Summer photos 8: a horseshoe crab

Sunrise in the field on a flat calm spring tide.

A horseshoe crab, Limulus polyphemus, surrounded by many many mud snails.

Well, this is it, the last week before school starts. And then I will be in the awful part of the year where I am juggling lab, field, and school responsibilities. Before that happens, I went out in the field to collect more snails. It was a beautiful morning, and I was there just as the sun was breaking over the horizon. It was a dead-calm day, as you can see in the first photo up there.

Among the many interesting things that I saw was this female horseshoe crab (Limulus polyphemus). These guys are really amazing. They are not really crabs (not crustaceans), but are more closely related to arachnids. They have remained morphologically the same for hundreds of millions of years, and are different than anything else I have seen on the shore. There's just one species in this part of the world, and I'd never seen it before moving to where I am now. But here they are all over, and I have collected molts of all sizes. One of the coolest sights on the beaches here is in May/June during the spring tides, when they come up onto the beaches by the hundreds to mate. I often barely miss stepping on them as I am walking around in the intertidal. This female got caught high on the shore at low tide, so she dug herself in to stay damp until the water comes back in.

Horseshoe crab blood has many different medical uses, and their eggs are eaten by many species of migrating shorebirds on the east coast of the U.S. Unfortunately, due to heavy use of the species as bait and to habitat destruction, their numbers have been declining for decades.

A deceased horseshoe crab with C. fornicata and C. plana attached. The size of the C. fornicata indicate that they were probably growing there while the crab was still alive, impeding respiration and locomotion. Photo by J. Browne.
They're also very cool because of how different they are from any other group that we study in invertebrate zoology. One of the things that I will miss when I leave this area is seeing them in large numbers, often with their carapaces bedazzled with Crepidula shells.

Sunday, August 18, 2013

Summer photos 7: the Bay of Fundy

I'm taking things a little out of order today, chronologically, because school starts oh-so-soon and I want to make sure that I get this post written before it does.

In late July, I went on a snail-hunting trip to the northern end of Nova Scotia (Cape Breton). Those photos will be forthcoming. But what matters for today is that this entailed an epic drive across the northeastern bits of both the U.S. and Canada. I had constraints on my time due to things happening in the lab, but also on a more immediate basis because of the tides. Since I can only look for snails at low tide, and low tide is only at a particular time, this means that I often have more time than I need to drive from point A to point B on any given day, leaving me time to do a little bit of sightseeing.

On this trip, I took a short detour through Fundy National Park in New Brunswick. I very sadly did not have time to explore either the bay or the hiking trails, but it was a nice drive.

The Bay of Fundy is notable for having the highest tides in the world. What that means is that the difference between high tide and low tide is larger there than anywhere else (an average difference of 47.5 feet during spring tides). There are also whales in the bay, and tidal bores where the rushing tides run into rivers and cause the rivers to change direction at certain times of the day. For a marine ecologist (or at least for me), this is something of a pilgrimage to go see.

Fundy National Park, New Brunswick. I'm not sure when in the tidal cycle this was, but somewhere in the middle.

Tidal flats at Fundy National Park.

Low(ish) tide at St. Andrews, New Brunswick. At high tide the water would be up near the pier, which is probably 10-12 feet high. Also note the abrupt change in the weather from the previous day. This made for more unpleasant driving.

Another shot of the Bay of Fundy, this one from a previous trip to Quoddy Head, Maine (the easternmost point in the US. This was taken only 1-2 hours before high tide (there's 6 hours between high and low tide), and by the time I left the park all of this rockweed was underwater.

I still have not had the opportunity to really explore the Bay of Fundy. Someday I definitely want to go see its more famous landmarks, look at the whales, and really explore its lower intertidal. For now, I'll have to content myself with pretty views from pretty high up on the shore.

Friday, August 16, 2013

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.

Wednesday, August 14, 2013

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.

Thursday, August 8, 2013

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.

Tuesday, August 6, 2013

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.

Friday, August 2, 2013

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.

Thursday, August 1, 2013

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.