Charles Darwin is, oddly, still as polarizing today as when he was when he published his first book. Evolution, obviously, is a slow process. Darwin, like other cultural touchstones before him, has been turned into a two dimensional historical character but, as one might expect, his life and work is interesting even beyond material for another feature about religion versus science. For instance, the man spent much of the latter part of his career consumed by Semibalanus balanoides. Barnacles. He studied them for eight years. It was a modest area of research for such a influential scientist, but the man was a naturalist. And there is much about barnacles to hold one's interest. They have, for instance, one of the largest penises, relative to body size, in the animal kingdom. When one spends one's life glued to a rock, it's important to be able to reach about for a mate.

Barnacles are also famously hard. They have to be to survive in the inhospitable environment they've chosen: the rugged intertidal zone. Marine organisms are spoiled by the user-friendly medium in which they have taken up residence. Fairly constant temperatures, healthy salinities, and eternal hydration make the ocean a decent place for even relatively rudimentary animals to live and thrive. Life in the intertidal zone presents the challenge of surviving without all those things for part of every day. When the tide rolls back and barnacles are exposed to a hostile climate. The higher in the intertidal zone organisms reside, the more difficult the jarring transition from marine to terrestrial can become.

Hence the hardness underfoot. Even if exposed to the air for half the day, barnacles have a hard calcium carbonate shell to retreat to. Not much water escapes, so the barnacle can stay soaking even as it bakes in the sun. It makes sense that this sort of adaptation would have appealed to Darwin. These little filter feeders epitomize the issue of zonation. If an organism can figure out a way to survive in higher intertidal zones -- if it can stay hydrated, get the food it needs and deal with fluctuating temperatures -- then finding a place to live is relatively easy. Existence becomes harder not only for you, but for your competition as well. An organism that figures out how to deal with one or two hours a day of exposure can fight in the low intertidal zones for space, but creatures like the barnacle, those who have figured out how to sun bathe for hours on end, have the run of the high intertidal zone. Zonation is a classic example of competition and adaptation at work, and the barnacle is the classic zonation critter. It's really no wonder Darwin was so fascinated. (And, seriously, let's not forget about the monster penises. Bigger than the entire rest of the barnacle body.)

Intertidal zonation affects competition up and down the food chain. The hyper competitive, ubiquitous Ascophyllum species (these are likely the plants that come to mind when someone says "seaweed") tend to run wild over the lower and middle intertidal zones. It's in the higher intertidal zones that one is more likely to find leafier, algal seaweeds. It seems a bit counterintuitive, that the thick leathery Ascophyllum would be the ones to stake out the comfortable lower zones, but they do because they can. The things that make them tough make them resistant to predation and they can stand living among limpets and other grazers.

Leafier, more delicate types are better off trying to crack the problem of spending more time out of the water so they can live higher up the shore, away from hungry predators. The heavier seaweeds that can stand some predation in turn make the lower intertidal zones an even more hospitable environment, providing a thick canopy, which makes good shelter for periwinkles and limpets. And those creatures in turn graze away that competing, fast-growing leafy seaweed and keep it from getting any ideas about making a run at the sweet life in the lower tidal zones. One group of weeds has figured out how to survive predation, the other exposure, and both have found substrate and a niche to live in.

It's less strange than it at first seems that Darwin would spend nearly a decade studying acorn barnacles. The varying tidal levels along the coast do provide a neatly ruled set of environments in which to watch his seminal ideas work themselves out. And, if one has to choose, the beach is always a better place to be than a courtroom in Dover, Pennsylvania.

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