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.