Field Study Report: Gulf Coast Dunes

Ardea herodias on February 8th, 2014 in Gulf Coast National Seashore near Pensacola Beach. This photograph, titled Dune Heron, won second place in a college photo contest. It captures the life of a coastal hunter during his down time.

Purpose

            The purpose of this field trip was to help the students understand the place of the organisms that they had studied in lab and lecture in the places where they naturally occur. Studying organisms in a classroom setting is a good way to think about process details or certain aspects of anatomy and their function, but another branch of zoology involves the life and interactions of those organisms themselves. The only way to truly understand the way organisms interact with one another is to observe them in the field in relation to their contemporaries.

Description of Habitat/Organisms

            This narrow strip of land before the forested panhandle of western Florida is a monument to change and diversification. Every year, tropical storms ravage this protective band of sand pushing the dunes even higher. In the past, it was storms like these that drove the formation of the islands and lagoons along the Gulf of Mexico. It is likely that these particular island chains began to form shortly after the Global Flood and again after the earth began to warm once again following the Ice Age.

Today, these dunes continue to shift and move, housing a unique and adaptable community of organisms in a variety of special habitats. In the lagoon on the sound side, a competitive shallow water ecosystem thrives. Pushing through the soft muddy or sandy bottoms of these shallows is a great diversity of invertebrates. Naticidae (moon snails) sink deep into the substrate, pushing it around their large fleshy bodies so only their hardened shell remains visible. I picked one of these shells, which appeared to be empty. However, no space is wasted in nature; the surface of the shell displayed a diversity of smaller gastropods, the Orthogastropoda (limpets), which had colonized the space to feed on algae. An ornately patterned leg tucked away deeper into the shell revealed another opportunistic renter Clibanarius vittatus (stripped hermit crab). In fact, there seemed to be more Clibanarius inside snail shells than there were snails.

One of the top predators in this ecosystem is Dasyatis (the stingray). This member of Class Chondrichthyes is a patient hunter of invertebrates, often burying its body in the sand. Fortunately for the zoology class, the tail remained unconcealed as some students approached. Soon the ray was on the beach; the subject of a very hands-on Chondrichthyes anatomy lesson. It was a fabulous way to connect students with an animal that might be otherwise difficult to relate to. After spiracles, gills, and spine were accounted for, the ray was released back into the lagoon. Unfortunately, it took some time for the ray to work out the aches, pains, and unconsciousness associated with asphyxiation.

However, a sound drew away from the main body of water. In a muddy slough leading away from the bay, Mugilidae (mullet) were jumping. In the shallows, some species of Fundulus (topminnow) schooled. Snails, with their spiraling shells bleached white by the relentless sun, clung to the rushes at the water’s edge. Calidris alba (sanderlings) and C. alpina (dunlin) poked through the mud on the shore and some members of the Anatidae (ducks) whistled nervously as they moved farther up the slough. Even a green heron flushed from the undergrowth. However, another bird caught my eye as it stalked out of the rushes; Rallus longirostris, the clapper rail. I had only ever seen a rail once before and that for only a fleeting moment as it flushed from in front of me. What struck me most about this bird was its way of moving. I had expected it to move something like a heron or egret but, rather, it stepped deliberately and almost awkwardly, like someone walking under a spruce tree in bare feet. It seemed so untypical—almost prehistoric.

Moving farther from the main group, I wandered up into the network of dunes. Anolis carolinensis (green alone) scampered into the thorny vines and cacti of the dunes. Many tracks were seen from animals as diverse as raccoons, deer, and mice. Reaching the top of one of the dunes, I was surprised to notice a freshwater pond, nestled among the withered skeletons of trees and sedges. Once there, I discovered life was again flourishing in unexpected places. Judging from tadpoles alone, there were at least three species of frog that bred in this small, warm pool. At the bank, some frogs were jumping, but they avoided landing the water. Rather, the tended to move into the sedges at the pond edge where I repeatedly failed to catch them before they almost magically disappeared. One frog, a Lithobates sphenocephalus, did jump into the water, but only long enough for me to identify it. Then it was gone, like all the others, into the reeds. Surprisingly, the pond was also home to a number of gaudy fish, defending their nesting territories from other fish. Judging from my photographs, these were a species of pupfish, Cyprinodon variegatus (sheepshead minnow). How any of these freshwater species managed to get out on this desert-like strip of land is beyond me. However, I imagine that many of these species harken back to a warmer period, before the onset of the ice age.

Discussion of Organism

            Certainly the most memorable species I encountered on this filed trip was Rallus longirostris. It was not an easy identification, however. The short tail and long orange-colored bill certainly gave credence to its status in Genus Rallus, but another species, R. elegans, is nearly indistinguishable to an amateur like myself. Thankfully, I was able to get a photograph before the timid bird wandered back into the rushes and its weaker flank bars were the give-away. Rallus belongs in the class Aves, the order Gruiformes, and the family Rallidae, which also includes the gallinules and coots. However, I am not certain that Rallus could be considered as the same created kind as the other members of the family. Their long bills and narrow toes, at first glance, seem to distinguish Rallus as a distinct monobaramin and possibly deserving of their one holobaramin.

            I am fascinated by the ancient nature of the Rallidae. It seems that, in 2001, Drs. Storrs L. Wilson and David B. Wingate were asking some of the same questions about Rallus. The paper they published that year in Volume 14, Number 2, pages 509 through 516 of the Proceedings of the Biological Society of Washington, “A New Species of Large Flightless Rail of the Rallus longirostris/elegans Complex (Aves: Rallidae) from the Late Pleistocene of Bermuda,” discussed the new discovery of R. recessus. It was from a cave deposit on the island of Bermuda, along with some other Ice Age animals, providing a glimpse of some of the diversity among rails at that time. It was very similar to R. elegans, with the exception of a very reduced keel, evidence that it was indeed flightless. Like many bird families during the Ice Age, it seems that some island forms of Rallus became flightless.