by Caroline Wiernicki -- June 27th, 2016
“There’s something big out there.” I fold a hand over the top of my eyes in a vain attempt to shield out the sun’s glare. A pair of triangular grey fins slice through the surface and disappear again. “There. You saw that?” Asya grins at me.
“Dolphins. Hurry up and put your mask on.” Already wearing hers, she shuffles her fins backwards into Francis Bay. I glance up at the sky—it’s a hot, clear day, with the blue punctuated by a crying cloud of pelicans and gulls. They hang above the water—above where I saw whatever I saw—occasionally cannoning into the bay, beaks open. The tourists lining the sand further down the beach seem to not notice the commotion. I grab my mask and my camera and—after an equally awkward shuffle backwards—dive into the shallows.
There were no dolphins in Francis Bay the morning Asya and me set out to place the PVC pipe markers for my first study on the invasive seagrass, Halophila stipulacea. Rather, those fins cutting up the water beneath the gulls and pelicans belonged to Megalops atlanticus, or the tarpon. Or, rather, multiple tarpons; at least thirty tarpons; at least thirty big tarpons. The screaming cloud of birds above the water had nothing on the commotion going on below. Our predators were in pursuit of prey, and—as we quickly discovered—breakfast consisted of a couple tens of thousands of baitfish. A fish an inch long—and so many that they blocked out the sun beneath them. We swim to the middle of this silver channel and—by some unseen force of decision or instinct—the tiny fish shift as one, closing a shining bait-ball around my manager and myself. Their rhythm is interrupted by the lazy glide of the tarpon. If the baitfish are bullets, then the tarpon is a torpedo, sending the smaller fish into a silver explosion of panicked scales.
Right. Seagrass. That was why were were here. It was only the first of three sites for the day, and we had already spent over an hour watching the tarpons hunt. We had work to do. As a brief recap, may I remind you that this particular study observes just how well—or perhaps how poorly—H. stipulacea can displace native grasses, such as turtle grass. The plan was to drive ten PVC pipes into the borders of where the invasive meets the native and to measure any encroachment over the course of the next few months. Simple enough. We had the pipes; we had the sledgehammer; and, at least insofar that morning at Francis Bay, after a quick recon, the invasive appeared to be everywhere. When discussing the set-up with Asya the day before, I anticipated that the total time to place the pipes shouldn’t take more than half an hour for each site. The only aspect that should really take much time would be finding the stuff, and H. stipulacea was really easy to find; and, I reasoned earlier, of course we should be able to identify turtle grass with ease—it’s just about everywhere, too.
I don’t start to panic until I’ve snorkeled well past the feeding frenzy. Here, the water is calm, clear, and empty. No baitfish, no tarpon, and no turtle grass. I try for deeper water and am met with a carpet of invasive grass. I can hear the pelicans splashing back down the beach where we started. I had always heard from professors, classmates, and colleagues about the need for flexibility in the field; what you expect to find is, more likely than not, not what will meet you. As I drift back towards the top of the beach, I kick myself for not having a better thought out contingency plan. What did I miss? Where is all of the turtle grass? This is borderline embarrassing. (Bad pun intended). What adjustments will I have to make if I can’t find a margin of stipulacea and testudinum? What will this imply for the rest of the study and the other bays? Is there something else, some sort of c-factor involved that caused the grass to decline, or can I just not find it? Asya looks at me, waiting. What do I do?
At this point I’ve made it back to the initial site where we got into the water, a couple of meters inshore away from the continuing feeding frenzy. I am searching for a lonely patch of manatee grass—another native—that could potentially be used as a proxy. Between the efforts to maintain consistency across the other two sites, and the plethora of potentially interfering variables—differences in growth rate, in natural densities, in habitat limitations—switching measurements is not something I want to do. I dive down, gently guiding a cloud of baitfish away—I can’t even see the bottom, they are so dense. Then I laugh. I surface, yell over to Asya, and I laugh. I dive back down—its fairly shallow here—and I grin around my mouthpiece at the patch of flat, long grass waving at me in between the schools of little fish. I swat, and the silvery channel parts a little more, and a little more turtle grass appears. As I lean closer, a four-foot-long tarpon drifts past my elbow, scaring more baitfish and exposing more turtle grass. I race away and out of the water to grab the pipes and hammer from where they sit waiting on the beach. Asya and I take turns hold pipes down and hammering them deep into the sand. By the time we are done, the baitfish still haven’t cleared away, but now swirl around a winding line of white tubes poking above the grass.
The rest of the set-up after Francis Bay was—wonderfully—uneventful. A curious sea turtle in Waterlemon, and a few curious beachgoers at Maho. Plenty of turtle grass and plenty of H. stipulacea to go around at both. As far as preliminary observations, one pattern among the sites that I did notice was a seeming decrease in density of each grass species upon their meeting. While I could identify borderlines between the two, the coverage appeared substantially thinner at these converging boundaries. Whether that has anything to do with each species filling in new growth and slowly spreading out to each other, or whether one is having an adverse impact on the other—I don’t know, or at least I cannot say anything yet. We will return to Francis, Waterlemon, and Maho in a few days to check that the pipes are still there, and then in a few weeks to take the first round of measurements. Until then. In the meantime, I’ll be brainstorming a few more backup plans, should another unexpected tarpon—or, dare I say, tourist—swoop in on the pipes.