Hacking spring: what to do when things are slow in the field

Spoiler: spring progress this year is slow. The cyprids continue to settle.

An oyster shell (Crassostrea virginica) covered with newly settled barnacles.
The redder dots are the younger larvae, and the gray ones are slightly older. 

A cement wall at my field site. It's hard to tell in this picture, but the reddish tint that you see between the large white pebbles is entirely due to a dense covering of newly settled barnacles.

The snails are just starting to come out in the field, and the water is warm enough that the Crepidula are finally brooding eggs. That means that they should be ready for experiments in a few weeks. Until I can reliably collect larvae in the field, I've been making do with what I can farm in the lab. That has meant collecting animals and bringing them up to room temperature, which triggers them to lay eggs. If I keep the females in clear plastic cups, I can watch the embryos develop and collect the larvae when they are ready to hatch.

Developing C. fornicata egg mas in a plastic lab cup. The female is probably about 30 mm long, and you are looking at her underside (ventral side). The solid arrow indicates the egg mass, which is full of little yellow dots. Those are the individual eggs. They are just laid, and have not really started developing yet. As the embryos develop and grow into little larvae, they will change color -- that's the signal I'm looking for to indicate their readiness to hatch. The dashed arrow is the foot of the animal. The egg mass is obscuring the head of the animal; she is brooding the eggs between her neck and the cup. 

This is a nice, convenient way to get lots of larvae for experiments year-round. The animals require extra care in the cups (each one needs to be fed daily and given clean water every 2-3 days), but sometimes this also means that I can get developing larvae as a side effect when working on other experiments with these adults in cups.

The barnacle life cycle: a photo essay

In my last post, I talked about the many settling barnacle cyprids that indicated the arrival of spring around here...but without any good photos of what these larvae actually look like. So here is a brief post on the life cycle of a barnacle.

Barnacles are crustaceans, the same group that contains the more familiar crabs and lobsters. This means, among other things, that they have an exoskeleton and jointed appendages. But they live attached to rocks, covered with a calcareous test, with no sign of those appendages (at least when the tide is out!).

Adult barnacles. Photo from Wikipedia.

When covered with water, though, their jointed legs (cirri) extend from those tests and catch phytoplankton that floats by. 

Feeding barnacles. The feathery things are the cirri. Still from Wikipedia.

Because the adults live cemented to rocks, it is the larvae that do most of the dispersing. Barnacle larvae go through many molts in the plankton as a nauplius.

Nauplius larva. Still Wikipedia.

Then, when they are ready to settle and metamorphose, they turn into cyprids. It is these cyprids that search out a place to live, contacting various substrates and searching for the right physical and chemical conditions before metamorphosing into their adult form. Barnacle settlement is ubiquitous in these parts, and relatively easy to settle, so it has been a mainstay of larval ecology for decades. We arguably know more about how and why barnacles choose their settlement sites than any other taxa. It depends on a variety of physical factors (for example, they preferentially settle in cracks on rocks) and chemical factors (they are attracted to proteins produced by conspecifics).

Here is one of the cyprids I collected this weekend.

A cyprid larva. Many lipid droplets at the anterior end provide buoyancy and energy for the larva.

I have thousands in the lab right now -- if I give them the appropriate settlement cues, I'll be able to watch them metamorphose, and the barnacle life cycle will be complete. (Well, except for gamete production and mating...perhaps left for a future post?)

All of a sudden, spring

I had a post all planned bemoaning the fact that spring is still very far away in these parts. In previous years, the snails are often laying eggs by this date on the calendar. Given the winter we've all had, it's no surprise that they are still nowhere to be seen, let alone reproductive.

I went to the beach on Tuesday (the day after a freak snow) to bring snails back to the lab for some experiments, and this is what it looked like.

The beach on a not-quite-spring morning.
The profile of the beach is still very steep due to winter erosion, and there were very few signs of life.

Berms of dead Crepidula fornicata shells were everywhere on the beach.
That's typical for late winter around here.

But today everything seemed different. It was the first day I was able to go exploring in shirtsleeves this year, and I went down to the harbor to get seawater for the lab. We don't have running saltwater in my building, but we are close enough to the shore that I can go get it when I need it. I found this.

Cyprids! Each of the brown blurry dots in the water is a larval barnacle, looking for a place to settle.

Cyprids, not yet metamorphosed, that have attached themselves to a dead blade of grass.

Cyprids are the last larval stage of a barnacle, and their job is basically to find a place to live as an adult before metamorphosing. They look like little beans with eyes and antennules that they use to sense physical and chemical cues on the substrate. They tend to settle gregariously, preferring to be near other cyprids and adults of the same species.

These cyprids have metamorphosed and become juvenile barnacles. They are probably not long for this world, because this dead blade of grass is not a stable habitat and will almost certainly wash away before the barnacles become adults.

The cyprids are the first clear sign of spring around here, as reliable as the many signs used in the terrestrial world to indicate that we are finally through the winter. So in the few short days since my field trip on Tuesday, things have turned a corner and are looking up. Field season is imminent.

Marine diseases, sea stars, and why it might matter

A sea star that I found on a collecting trip in September.

 It's deep winter here, the kind that has us shoveling new snow more days than not and the animals on the beach dealing with all sorts of ice and snow, so I have more time for the blog than at other points during the year. It reminds me of my childhood winters elsewhere in the country much more than a normal winter here on the coast. So hi again. This time with content.

There are several conservation issues in the marine realm that make the news with some regularity. Climate change, of course, and overfishing, and the relative new kid, ocean acidification. But the latest issue that's making headlines is a catastrophic decline in sea star populations along the Pacific coast of North America. This decline is sudden and unexplained, and although the evidence is consistent with a disease, no one really knows yet just what that disease might be.

Yes, marine invertebrates get diseases too. Scientists really know very little about what causes diseases in the marine realm, but we do have examples from coral, lobster, and oysters, just to name a few. It seems like we need to add sea stars to that list. There's even some indication that the frequency of diseases has been rising of late, possibly due to changing climates.

Here are links to places around the web that have explained the current sea star issue better than I can:

PBS recently produced a great clip on News Hour about the problem that I strongly encourage you to see. The scientists interviewed here are ones that I have met and interacted with, and people I really respect. It's neat to see them on TV. In fact, one of them has made a previous appearance on this very blog for her work curating the collection of glass invertebrates at Cornell University.

More scientific information is available here from UCSC.  This site shows you the different stages of the disease, and even includes a form for you to report sightings of diseased sea stars (for anyone who might be reading this in the affected Pacific Coast area).


And lastly, here's another great blog post about the subject.

But why does any of this matter? Well, for one thing, sea stars are a group of marine animals that people feel some sort of connection to. They are iconic images of the sea, popping up in jewelry, home decor magazines, and children's cartoons. But they are also important animals in the communities where they occur. Six months ago, I wrote about intertidal zonation on rocky shores. Sea stars are crucial players in keeping mussel beds under control by eating mussels (the stars are pretty voracious predators). In fact, they are the defining example of a keystone species: one that has a disproportionate effect on the community relative to its abundance. Remove the stars from an area, and the whole community structure will change.

So the disappearance of stars due to a mystery disease is pretty troubling. Hopefully scientists can at least figure out what is causing the decline while there are still sea stars left in some of these areas to save.

The underside of the same star. Note the tube feet that they use for moving around (operated by a hydrostatic skeleton) and the mouth of the organism, which is in the center where all of the arms converge. Sea stars eat by ejecting one of their stomachs and digesting their prey before ingesting it.

In the bleak midwinter

My field site under six inches of snow.

The high tide line becomes easily visible in the snow: it is where the water has washed the snow away. The beach itself looked normal, until I looked closely.

Ice in the intertidal. It wasn't even that cold this morning (right around freezing). The local flora and fauna are frequently affected by ice in this area, which will scour the rocks bare and create new habitat.

It was beautiful this morning, above freezing, sunny, and not windy. A nice break in what is promising to be a very snowy week. Conveniently (since I need the snails), this corresponded to a very low spring tide. Because many of my snails have been frozen off the rocks (see the third picture) I had to venture out into deep enough water that the snails had not been frozen yet this winter.

Update with snails

I know it's been forever since I updated. The semester started and hit me like the proverbial train, and since then it's been nothing but teaching and research at full-tilt. There was a collecting trip in there, and several experiments started, and a couple finished. I gave an invited talk for the first time at another university, and may have inspired a student to start doing research in ecology.

Here are a few select photos from the last two months:

A tidepool full of Crepidula plana and surrounded by barnacles. Photo taken in September on a collecting trip.

Seaweed (probably Sargassum washed up on a beach in Florida. The seaweed was full of little critters living on and in it, and at night something was bioluminescing in the seaweed clumps. Photo taken in October on a for-fun trip. I am astonished by the colors every time I see this shot.

My local field site, sunset, early November (the day before the end of daylight savings).

What inspired me to come back to the blog today was nothing that I have done, but rather this post from Rachel Collin's lab in Panama (I've mentioned their work with Crepidula before). One of the grad students in the lab has gotten actual video footage of mating Crepidula, and the videos are up on the lab blog.

Go. Check it out. It's really quite amazing.

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.

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.

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.