It’s dark this morning, but I spot four figures in brightly-colored clothing already on the beach just to the south of the fishing pier. A little annoyed that anyone beat me to the beach, I decide to go north. As I get closer, though, I realize that what I thought were human figures were actually just tied-up beach umbrellas, left in place overnight. I change my mind and head south, instead.
I walk a long way in the darkness, watching the sand for movement. All I see are coquina clams – lots and lots of them. Whole beds of coquinas, washing along in the swash zone. As I watch them, I notice something peculiar.
The coquinas near my feet do the expected thing: when the surf rolls back, they dig into the sand and disappear. However, the coquinas further down the beach slope don’t dig themselves in. As I watch, these clams dig themselves out! In a moment I have a guess as to why.
It’s around 6:00 am. Low tide was around 4:00, so this is an incoming tide. Of course, I realize with a start. The coquinas can’t only dig in. If they did, they couldn’t move with the changing tides. Instead, they must dig in only when they reach the top of the swash zone, and dig out when lower. That lets the incoming wave wash them up the beach.
I watch a few more beds of coquinas to see if my guess matches with their behavior. Yes! Every time I see a bed of coquinas down low, they dig out of the sand as the wave recedes. Then, when those same coquinas get washed up higher by the next wave, they dig into the sand and disappear beneath my feet. Amazing.
Next I realize that this behavior must change as the tides change. They can’t only let themselves be washed up the beach. They must also let themselves be washed down the beach during a receding tide! On Friday, when I’ll be on the beach all day long, I’ll test this guess against reality.
Of course, I know this isn’t some great discovery. It’s almost just common sense, and I’m certain if I studied the literature on coquina clams and the swash zone this behavior will be well-known and well-studied. But to me, it’s a new discovery, deep, beautiful, and exciting.
Like all such discoveries, it suggests far more questions than answers. I wonder next, how to the clams do it? How do they know when to alter their behavior? How can they tell if the tide is swelling or receding? I can’t tell, not without the internet in my pocket (or at least a tide table). How do these tiny mollusks know?
Are they programmed to their specific beach? If I took coquinas from this beach and placed them on another with very different tide times, would they ever adjust? Or is their internal clock independent of outside influence? How could so much knowledge reside in this tiny shelled creature?
Mysteries are wonderful things; I can’t wait to explore this one some more.
This long barrier island just south of Clearwater Beach is relatively litter-free; even so, I do come across the occasional thoughtlessly-left bit of trash on the beach. Now I find a gall0n-sized zippered plastic bag, and I decide to grab it. Plastic bags are the mortal enemies of sea turtles, who eat them thinking they are jellyfish.
Humans are remarkable creatures, I think as I carry the wet bag up the beach toward a trash can. We’re capable with our brains and our technology of utterly transforming an environment, making it totally unsuitable for the natives. We are also the only creatures that try in any way to mitigate their impact. Maybe I just saved a sea turtle’s life.
I decide to sit on a bench just there and watch the ocean for a while. The Sun is coming up behind me now and the gulf is turning green. Such a lovely sight. I will miss this when I’m gone.
Later, I’m lying on a boat ramp into the Boca Ciega Bay, trying to get a picture of a shy fiddler crab. The crabs scurry into their holes on my approach, but if I sit very still, they will eventually forget about me and come out. I get them to reappear, but only then think to take a picture. My movement to get my phone out spooks them, and they disappear. I prepare to wait once again, this time with camera aimed. Unfortunately, those clouds in the picture above are moving west to east, and as soon as they hit the cool morning air over the land, the skies open up and the rain starts pouring down.
I’m not concerned about myself, as the rain is just cool enough to offset the heat of the rising Sun. But I am worried about my phone, so I head for some shelter. There’s a trash can there, and ironically inside is a plastic grocery bag. I pull it out – still clean – and wrap up my phone. Now I can head back out, and I’m excited to do so, because I know enough geometric optics to realize what’s coming next. The Sun is in the east, where the sky is clear. The rain is coming in from the west. I’m about to see a rainbow on the beach!
As I head down the nearest public access, there’s the rainbow. Beautiful, and I immediately start thinking what I always think when I see this marvel. Does understanding the rainbow really make it less beautiful? Of course not. I think again about the coquinas, and my “discovery” earlier that morning.
The first person to understand where a rainbow would appear in the sky must have gotten an enormous thrill, the same thrill I received from my coquina realization. And just as with my coquina discovery (as Richard Dawkins pointed out in his book on the subject), learning one truth about the rainbow didn’t just answer questions, it raised them. Studying rainbows led to the discovery of the true composition of light, its various wavelengths and frequencies. This led in time to the connection between frequency and energy, which in turn led directly to quantum mechanics, the structure of the atom and, eventually, to the age, size, and birth of the universe itself. Not bad.
Between all this reverie and the plastic bag protecting my phone from the rain, by the time I got a picture taken the rainbow was just about gone. Who knows, maybe it wouldn’t have shown up, anyway; I’m still very new at this whole photography thing. But even without a visible rainbow (trust me, it was there just in the left part of the shot), I still think I managed a pretty picture. What do you think?
(Yes, that’s a sea turtle nest – though not “my” nest, it’s further off to the left – in the center of the photo.)
Only two more beach walks, and then it’s back to landlocked Ohio. Oh, dear.