Coastal Trail Natural History
These are some of the types of habitat that you will see while visiting the Coastal Trail of the Big Bend Scenic Byway, from the St. Marks National Wildlife Refuge to Apalachicola.
These are constantly reshaped by waves, winds, and tides. Waves and winds pick up sands and reshape the shoreline. Tides sweep sand, shells, and trash onto land and back out to sea. There’s so much change in this zone that vegetation doesn’t have a chance to get established. Both birds and sea turtles lay their eggs on beaches. Resident wading birds and migrating shorebirds feed at the water’s edge.
This long, narrow strip between the beach on one side (where plants can’t grow) and the much more stable communities on the inland side may be dry oak scrub, pineland, or”¨hardwood forest. It includes the inland edge of the beach as well as the dunes. Plants and animals must adapt to salt spray, wind, and occasional flooding to survive here. Most of the plant species are vines, grasses, and herbs (that is, non-woody plants). After a storm wipes out the plants the coastal strand is recolonized from seeds blown in on the wind or contributed in bird and animal droppings. Dunes can be formed when the wind hits plants such as sea oats. The plants slow the wind down just enough to drop the sand it’s carrying. Isn’t it remarkable that these plants can withstand salt spray and strong winds but cannot survive human footsteps?
The marsh’s boundaries are fluid, adjusting themselves according to storms, erosion, sedimentation, the ebb and flow and meandering of tidal creeks, and sea level changes. A salt marsh may not be much to look at but what it does for us is remarkable. These monotonous stretches of grasses produce an enormous amount of dead plant matter, which is quickly broken down by crabs and other little creatures into tiny pieces, called detritus, which in turn feeds the young of many fish and shellfish species that end up on our tables. Blue Crabs, Shrimp, Mullet, Spotted Sea Trout, and Large-Mouth Bass spend part of their lives in the marshes of the Apalachicola estuary. No marsh? No seafood. “¨You can detect where the tide is strongest by which species of grass is dominant. There’s”¨Smooth Cordgrass where the marsh is flooded by tides most frequently and Black Needlerush where the tides don’t reach quite as far. In transition zones between the marsh grasses and the adjacent uplands you’ll find Glasswort, Saltwort, and Marsh Elder. “¨Many of the salt marsh’s inhabitants are seldom seen but are sometimes heard. Listen for”¨the clack-clack-clacking of Clapper Rails and the piercingly loud song of the tiny Marsh Wren.
If you’re really and truly lucky you’ll hear the Black Rail’s “KEEE-KEEE-doo.” For many birders the Black Rail is a Holy Grail of sorts because it is so seldom seen “” and not often heard, either.
Scrub (Xeric Oak Scrub and Sand Pine Scrub) Scrub is miraculous. How can anything grow on old, deep sands that have practically no capacity for hanging onto water or nutrients? Yet trees, shrubs, lichens, and even flowering non-woody plants are found in scrub, along with a full list of animals. Along the corridor you’ll find scrub near the coast on sandy ridges that used to be either dunes or sandbars. As more and more sand accumulated shoreward of these once-coastal features and the shoreline moved farther and farther away, the formerly coastal features became inland communities. At least scrub plants don’t have to contend with the salt spray, windblown sand, and flooding that challenge coastal strand species.
A lot of the land in scrub has nothing growing on it and resembles a white sand beach with trees. Stunted-looking oaks, along with Saw Palmetto, are the dominant plant species in some scrubs; in others Sand Pine is the tallest plant. Scrub relies on fire to keep on being scrub. Without fire, other tree species (such as Live Oak, Laurel Oak, Red Oak, Sparkleberry, Pignut Hickory, Southern Magnolia, and Redbay) that can’t stand burning will establish themselves, and scrub will become a xeric hammock “” a different kind of community.
Sand Pine is unusual in that the cones in some populations are sealed with natural resin. Fire is required to open the cones and release the seeds. Fire kills adult Sand Pine, so once the parent population has been burned a new generation starts up from seed, resulting in a forest of trees all the same age. But other Sand Pine populations “” including most of those in the Panhandle “” do not have closed cones. Instead their cones open up and drop their seeds in the fall, perpetuating the species and resulting in a forest with trees of many different ages.
It takes a long time to accumulate enough fuel in a scrub forest to sustain a fire. As Sand Pine grows its lower limbs die but do not fall off the trunk. When enough dead limbs accumulate they may be ignited by lightning or another source and create high-intensity fires. In a Sand Pine forest where the cones are closed until fire opens them, a lot of seeds are released all at once. In an open-coned population Sand Pine can only regenerate if there are nearby unburned trees to supply seed. If no Sand Pine seed is available, or if fires are so frequent that Sand Pine doesn’t live long enough to produce seed, the forest will end up as an Oak Scrub.
These are stretches of shoreline that are protected from the waves that pound the beaches. Tidal flats are also known as mudflats (because their surface soils are muds brought in “¨by channels from uplands) and intertidal zones (because they are between the tides, exposed at low tide and flooded at high tide). We may not see much besides mud when we look at tidal flats, but many animals see breakfast, lunch, and dinner. A world of invertebrate animals lives in and on that mud, including Tube Worms, Sand Dollars, Burrowing Shrimp, Sea Cucumbers, and assorted Mollusks and Crabs. Not only are there lots of species, there are also thousands of animals per square foot. These invertebrates live on tiny bits of leaves and stems of both land and aquatic plants that are brought into the mudflats in freshwater channels or by tides. The invertebrates become food for fish and birds. When the tide comes in, fish come with it to feast; when the tide goes out, birds dig in. Tidal flats are essential refueling stops for migrating shorebirds.
Coasts & Estuaries
The Byway coastline spans two major estuaries: Apalachee and Apalachicola Bays, where fresh water from the land mixes with salt water from the ocean. This mixture has a level of salt (salinity) that’s somewhere between fresh water and salt water. Without this mixture the fish and shellfish industries, as well as sport fishing, would dry up.
Apalachicola Bay wears a necklace of narrow, sandy strips (St. George and St. Vincent Islands) that boast postcard-perfect beaches. Apalachicola Bay is a type of estuary called a closed embayment, where waves have enough strength to push sand into piles that create barrier islands. The Apalachicola River’s huge drainage basin also supplies sediments to the Bay and the river’s enormous contribution of fresh water carries these sediments into the estuary.
Because open bays are directly connected to the open waters of the Gulf of Mexico they are generally a little saltier than their sheltered cousins, the closed embayments. Both still qualify as brackish, however. Salinity Type of Water Salt content in parts per thousand Fresh Less than 0.5 Brackish (estuarine) 0.5 to 30 Salt (coastal ocean) 30-37 Estuaries are edged with beaches, salt marshes, or tidal flats. In and under the water of the region’s estuaries you can find:
Oyster bars (colonies of oysters), which are most common where the salinity is between 15 and 30 parts per thousand. Oysters can’t survive in fresh water and in saltier water they are attacked by predators, parasites, and diseases. Oyster bars provide habitat for a multitude of invertebrates and fish, including Sponges, Anemones, Whelks, Worms, Barnacles, Blue Crabs, Stone Crabs, Pinfish, Sea Trout, Spot, Black Drum, and Mullet. At low tide shorebirds, wading birds, and Raccoons help themselves.
Seagrass beds, which get their name from a half-dozen species of plants that flower just as land plants do, although they are not related to grasses that grow on land. Hundreds of algae grow on the leaves of these plants, which would smother them if it weren’t for animals that graze on algae, such as Pinfish. Grazers, in turn, are eaten by larger fish and invertebrates. The young of many fish and invertebrate species rely on seagrasses for food and shelter. Without seagrass beds we would have no scallops or shrimp and our fisheries would be much poorer. Sea turtles savor Turtlegrass and Manatees munch on Manatee Grass, which are two of the most widespread seagrasses in the area. Because seagrasses, like other plants, depend on sunlight, they cannot grow in muddy or very deep water.