Darwin’s Barnacles

As the weather finally gets a bit colder, I find myself drawn away from the water itself and more toward indoor places where I can grab a quick drink and a bite to eat. Recently, I ordered some oysters at a favorite bar where the oysters come straight from the left coast. Aside from the oysters being delicious (and Washington oysters being doubly so), the gnarled and fractaled shell provided a perfect location for a few barnacles to make their homes.

This provides a unique opportunity from an imaging perspective. Though I’m tremendously interested in barnacles (their life cycle is so tantalizingly weird), their preference for growing on rocks makes them pretty tough to look at unless you have an underwater rig or a tank in which to grow them. Mine live in an old takeout container that used to house Chinese food. Set up on oysters, they’re remarkably portable, which means their behaviors are also observable.

Most of my observations have been through a macro lens I made for my phone out of the lens of an old digital camera. It gives me this bit of footage of one feeding.

And this, more recently, of the same barnacle molting after a few days.

To understand the concept of a barnacle molting took me a few tries. It finally became clearer when someone pointed out that they’re crustaceans. Which is to say, a barnacle is essentially a shrimp that’s fused by its forehead to a rock and uses its leg hairs to catch food (like I said…tantalizingly weird). The molted skin provided an opportunity to see up close what the barnacle’s legs looked like.

I keep comparing the barnacle’s feathery filters to the images I’ve taken of spider’s legs. They share so many physical characteristics–long and spindly, segmented and covered in sensitive hairs–but for such different purpose (though one could argue that both are used to catch food; it’s only the methodology that changes). Under high magnification, we can see how these hairs branch out from the legs as flexible segments of their own (and provides an interesting image of the mechanism of the hairs at work).

Barnacle Feather High Mag 3 Barnacle Feather High Mag 2

It’s no wonder that Darwin found these creatures so fascinating, why he spent almost a decade studying them while he sat on his Origin of the Species. They’re such a great expression of the way modifications in the same forms can create whole new creatures with brilliantly different ways of living. The ability of the barnacle to claim a niche as a filter feeder, while only changing slightly (and very little from its life cycle) out of the form of the free swimming clam shrimp I found recently in fresh water is an incredible demonstration of Darwin’s principles.

Turning away, momentarily, from the barnacles, the oysters act as a tiny ecosystem in and of themselves. Present on their shells are what appear to be the skeleton of a small, flat coral (visible next to the barnacle at 40 seconds).

I have also found walking around the tank, a tiny oyster (too large to effectively image with a microscope) and the discarded shell of a small bivalve.

Cockle shell 2 Cockle shell 3

The ridges on its shell make me think it was some species of cockle, or possibly a scallop. And turning the scope to the body of a dead barnacle drifting in the water, I find this swimming around.

It’s not clear to me exactly what it is. A rotifer perhaps. It’s ability to move incredibly fast reminds me of a previous post of other protozoa seeming to move at the speed of light.

This makes me want to engage in a new experiment. The common refrain about oysters (eaten raw) is that they taste like the ocean from which they come. I’ve observed this is true. Atlantic oysters on the whole are saltier in flavor, while the Pacific tend to have a more creamy, vegetable taste to them. I suspect some of the reason for this is that the oyster literally traps parts of the ocean in its liquor, so that when we eat an oyster, we’re eating some of the ocean they come from. What I wonder is how much of that ocean has been trapped and how much of an ecosystem is contained therein. Even scrubbed, shucked, and served on ice, these oysters have proven to contain whole worlds on their shell. My next step, then, is to catch some of the water in their shell and see what I find there.


9 Comments Add yours

  1. laksiyer says:

    This is brilliant Matt. I have only read about barnacles, never studied them. Wow this is just amazing. You got to tell us about your tank setup so that it can be repilicated. I also liked that single type of ciliate that you have in one of the videos. Wasnt it in one of your previous videos too? The clonality suggests that it might be barnacle associated. If you get that ciliate in highpower, that would be great.. Yes that looks like a polyarthra rotifer, with saltatory movements.

  2. Matthew Rossi says:

    Laks, my tank setup is so simple it’s absurd. It’s a shallow plastic takeout container I got from a Chinese food delivery several months ago. Plants in the tank churn out oxygen, while the barnacles, which are filter feeders after all, filter much of the bacterial life that produces the uglier chemicals. At least, that’s my working theory. The other “tank” is a small gelato jar, again with seaweed acting as the primary oxygenator.

    My hope is that the barnacles will decide they’re close enough to mate and leave me with naupilii and later cyprids to look at.

  3. Aditi says:

    Awesome. Hoping to get near the ocean this spring break to make a few collections.

  4. laksiyer says:

    Awesome. Hoping to get near the ocean this spring break to make a few collections.

  5. Tom Hata says:

    Excited to see barnacles on the site! One of my PhD studies involved building an artificial wave tank to see how barnacles feed in high flows (like the intertidal). Here’s a slowmo video of one of them feeding https://www.youtube.com/watch?v=9GpDss0YvzQ. I was feeding them brine shrimp eggs, which you might want to give a shot (throw a few in and stir them around so they don’t just sit on the bottom or top). In the video, I think you can see the barnacle actually catching an egg in its setae (hairs).

    I’m mentioning the brine shrimp eggs because some species can filter out bacteria but mostly they need bigger things to feed on to stay happy. I’ve had some that lived for over 3 weeks without food in an aerated and chilled container but they definitely were hungry.

    Interesting fact, the morphology of their legs and the spacing of their hairs change dynamically between molts if they’re in different flow conditions. Theoretically this is to optimize their ability to feed in a given flow climate!

  6. Saad Bhamla says:

    Beautiful videos @Matt…
    I couldn’t help smile at your tank setup description 🙂 Sometimes we all think science is done is hi-fi uber complicated setups in hi-tech laboratories – whereas the world can actually be observed simply – on dimes and nickels. Time is the only thing holding most people back – and effort 🙂

    So inspired by your videos to start my own mini aquatic eco-system.. I have a collection of ciliates for now. Will bring in more organisms slowly 🙂


  7. Matthew Rossi says:

    @Tom good to know about the feeding. I assumed they were smaller protozoa eaters, not larger food. I’ve got a couple of setups going right now. The Pacific tank (where the barnacles live) is pretty murky at the moment, and seems to have a good amount of plankton swimming in it (copepods and the like), so I think they’ll be ok for a bit. I ordered some eggs just in case, though. I’ve started my experiment to investigate the relative ecosystems of the oysters today. So far, I notice larger numbers of barnacles on the Washington oysters, larger numbers of limpets on the Massachusetts. Imaging all the way.

  8. Matthew Rossi says:

    True story: I recently had a problem with a set up with some urchins. They were living in far too close quarters and, unfortunately, died before I could look at them. Barnacles seem like they must be hardier creatures, if for no other reason than they’re adapted to not having water on them for long periods of time (also, these have survived a trip cross country in a refrigerator coma), but I’d like to avoid a repeat of the previous mass die-off.

  9. Manu says:

    Love your “hypothesis” that the ocean flavor has more to do with the ecosystem instead of the water. That is a very creative conjecture and truly exciting to explore..

    I love oysters; so you have given me ideas on what to do with all the dozen oysters I eat in one single sitting.

    Very inspiring work Matt.


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