Big Bend Coast
The Big Bend Coast is the marshy coast extending about from the western end of Apalachee Bay down the west coast of peninsular Florida to the Anclote River or Anclote Key. It partially overlaps the coast line of the Big Bend region of Florida, and is coterminous with the coast line of the Nature Coast region of Florida. Most of the coast remains undeveloped, with extensive salt marshes, mangrove forests, seagrass meadows, and oyster reefs offshore, and coastal hammocks onshore.
Geography
The Big Bend Coast is variously defined as extending from the mouth of the Ochlockonee River, or of the St. Marks River, at the western end of Apalachee Bay, to the mouth of the Anclote River or to Anclote Key, just offshore of that river mouth. It is sometimes divided into two parts, the Big Bend Proper, from the Ochlockonee River to the Withlacoochee River, and the Springs Coast, from the Withlacoochee River to the Anclote River. The northern part of the coast, the Big Bend Proper, is sometimes further divided into four areas for study and discussion purposes: Apalachee Bay, Deadman's Bay, Suwannee Sound, and Wacasassa Bay. The Big Bend Coast is sometimes a component in the larger Wilderness Coast that also includes the coast west of Apalachee Bay to Cape San Blas. The Big Bend Proper includes the coasts of Wakulla, Jefferson, Taylor, Dixie, and Levy counties, while the Springs Coast includes the coasts of Citrus, Hernando and Pasco counties.Geology
The Big Bend Coast is a drowned karst region, covered with salt marsh and mangrove forests. It includes freshwater springs, oyster reefs, and the delta of the Suwannee River. There are barrier islands west of the Ocklockonee River and south starting with Anclote Key, but there are no barrier islands between those places. The Big Bend Coast has little or no sand or mud. The karst topography has produced an irregular, frequently exposed, bedrock surface. The lack of sand has been a feature of the Big Bend Coast since at least the Pleistocene. Sediment of Holocene origin is generally limited to salt marshes and the nearshore zone, and is redistributed by tidal action and storm events. The Suwannee River carries about 73,000 metric tons of sediment to the coast each year. The Big Bend Coast is on the Gulf Coastal Lowlands of Florida, which has recently exposed ocean-smoothed terraces with Tertiary limestone at or just below the surface. The flatness of the Big Bend Coast is interrupted by an area of relic sand dunes just inland from the Cedar Keys. The presence of a high water table has produced a karst landscape. The limestone hosts the Florida aquifer, which reaches the surface near the coast. Steady discharge from the aquifer supports the discharge of the many springs feeding rivers and streams along the coast and maintains a high water table near the coast.Freshwater sources
Rivers
All of the rivers that reach the Gulf of Mexico along the Big Bend Coast are at least partly spring-fed. There are 14 rivers reaching the coast between the Ochlockonee River at the western end of the Big Bend Coast and the Anclote River at the southern end, including the St. Marks, Aucilla, Econfina, Fenholloway, Steinhatchee, Suwannee, Waccasassa, Withlacoochee, Crystal, Homosassa, Chassahowitzka, Weeki Wachee, and Pithlachascotee rivers, and Spring Warrior Creek. Largest is the Suwannee River, with a small delta near the middle of the coast. The coast between the Withlacoochee and Anclote rivers is known as the Springs Coast. Four short rivers, the Crystal, Homosassa, Chassahowitzka, and Weeki Wachee rivers, are fed almost entirely by first-magnitude springs, as there is almost no surface runoff in the area. The entire lengths of the Crystal, Homosassa and Chassahowitzka rivers are subject to tidal influence. At the southern end of the Springs Coast, the Pithlachascotee and Anclote rivers arise further inland, but are almost entirely spring-fed.The many rivers and smaller streams flowing to the Big Bend Coast lower the salinity of the nearshore water. The seasonality of rainfall produces seasonal variations in the salinity of the waters along the Big Bend Proper. Rainfall from tropical cyclones may also lower the salinity of nearshore waters. The shallowness of nearshore waters also mean that the water temperature is strongly affected by the air temperature. Tropical species may be killed by cold weather, or may migrate southward or to deeper water less subject to cooling in winter.
Other freshwater sources
Besides rivers and streams, hundreds of springs, fractures and seeps along the Big Bend Coast contribute to the flow of freshwater into the Gulf of Mexico. The close proximity of the Florida aquifer to the surface with only a shallow soil layer over the porous limestone bedrock means that groundwater can emerge in many locations. The water discharged by the Florida aquifer to the surface has a temperature of year-round. On winter nights the waters of the Gulf are significantly cooler than the water emerging from the Florida aquifer. Thermal images were taken at night in March 2009 along of the Big Bend Coast from Jefferson County to Levy County. The thermal images revealed 874 "hot spots" along the coast which were at least warmer than Gulf waters in the study area. One hundred ninety-three of the identified sources were under water in the Gulf. The authors estimated that the discharge from the identified inland sources is equivalent to that of one 1st-magnitude spring for every of coast.The streams and springs flowing to the Big Bend Coast contribute approximately of freshwater to the Gulf of Mexico each day. Livingston describes the Big Bend Coast as a massive, open estuary.
Intertidal zone
The Big Bend Coast is subject to little or no wave energy. Tidal range is for all of the Big Bend Coast. In the mid-20th century the intertidal zone of the Big Bend Coast consisted of salt marshes up to wide, dominated by herbaceous plants, including Juncus roemerianus, Distichlis spicata, Sporobolus pumilus, and Salicornia species. There were about of tidal marsh along the Big Bend Coast in 1997. The marshes grow on sediment that is usually no more than thick, although some depressions in the karst bedrock may have thicker deposits. As of 2023, mangrove forests are replacing salt marshes in the intertidal zone along the southern part of the Big Bend Coast from the Cedar Keys to Anclote Key. Mussels, oysters, fiddler crabs, marsh periwinkles, crown conch, flathead grey mullet, and blue crabs are abundant in the salt marshes. The vegetation of the salt marshes have been called "perhaps the most productive in the world." Salinity levels and temperatures can seasonally become extreme in salt marshes, potentially killing many fish and invertebrates. Most species found in salt marshes have developed behavioral strategies, such as migration, to cope with the extremes. Marsh creeks carry freshwater runoff from the land to the gulf, and provide another habitat for many species. Glass shrimp and killifish are lifelong residents of marsh creeks. Pink shrimp, blue crabs, stone crabs, mullet, red drum, and Gulf flounder live in marsh creeks as juveniles. As a result of sea level rise, salt marshes have been retreating along the Big Bend Coast, but losses on the open water side have been more than offset by the replacement of coastal forest with new marshes, so that the area of salt marshes along the coast has increased by approximately 23% since the beginning of the 20th century.Oyster reefs
Although relatively rare, there are some outcroppings of limestone bedrock in the water along the coast. Oyster reefs are found on such outcroppings, particularly close to the intertidal zone in the nearshore zone. Oyster reefs often include mussels, slipper shells, and barnacles. Porcelain crabs, mud crabs, peppermint shrimp, snapping shrimp, annelid worms, gobies and toadfish commonly live in the crevices of oyster reefs. Oysters are preyed on by juvenile stone crabs, blue crabs, oyster drills, and crown conchs. Oyster reefs along the Big Bend Coast can be classified as "marsh-oyster", with oysters present as individuals or clumps in Sporobolus alterniflorus on fine sediment, and "sand-oyster", with oysters found on coarse sand and shell fragments with little of no vegetation. Marsh-oyster reefs occur primarily close to shore. The more common sand-oyster reefs are found from close to shore to approximately from the shoreline. Oyster reefs have been present in the area for 2,800 to 4,000 years.A study of oyster reefs in the vicinity of the Suwannee River delta found that the area of reefs in the study area had decreased by 66% between 1982 and 2010. The area covered by the reefs declined from 1982 until 2001, but appeared to increase between 2001 and 2010. The study found that the apparent increase in area between 2001 and 2010 was an artifact of reef collapse, in which reefs with a high density of oysters spread over a wider area with a much lower density of live oysters. On average, both reef collapse and total loss of reefs were higher the further the reef was from shore. Some increase in oyster populations was found in 2010 in areas closest to the shore.
Nearshore zone
The nearshore or littoral zone of the Big Bend Coast was estimated to have of seagrass meadows in 1999, consisting primarily of the seagrasses Thalassia testudinum, Syringodium filiforme, and Halodule wrightii. The seagrasses Halophila engelmannii and Halophila decipiens, and the salt-tolerant wetlands grass Ruppia maritima, are also found in the seagrass meadows. Green algae, primarily of the order Bryopsidales, but including some species in the order Dasycladales, are common, and a few brown algae, are either rooted to the floor of the littoral zones, or attached to seagrasses. Other algae, primarily red algae, but also including some green and brown algae species, drift in the waters around and above the seagrass meadows. In some areas algae outmasses the seagrass. Seagrass meadows stabilize the bottom and slow water flow, which lets suspended particles settle out of the water. This reduces the turbidity of the water, allowing light to penetrate deeper. As a result, the seagrass meadows along the Big Bend Coast extend up to offshore, in water up to deep. The seagrass meadows of the Big Bend Coast are among the largest and least disturbed in the world.The biological diversity found in seagrass meadows is surpassed only by coral reefs in Florida waters. Seagrass meadows host a wide variety of algae and animals. Red algae and filter-feeding animals, such as sea squirt colonies, sponges, pygmy sea cucumbers, and juvenile scallops, attach to the blades of seagrass, often remaining for rest of their lives. Invertebrates, including hermit crabs, stone crabs, various shrimp species, amphipods, isopods, brittle stars, asteroid starfish, sea cucumbers, pen shells, clams, scallops, sea snails, arrow shrimp and sea urchins live among the seagrasses. Some fish, such as spotted sea trout, seahorses, and pinfish live year-round in the seagrass. Other fish, such as black sea bass, gag grouper, and gray snapper shelter in the seagrass while juveniles. Atlantic Spanish mackerel, bluefish, crevalle jack, pigfish, and spot enter the seagrass meadows to forage.
The seagrasses of the Big Bend Coast are typically found in tropical waters, and are at or near the northern limit of their ranges. The lowest tides of the year generally occur in the winter, and expose the seagrasses to freezing air temperatures for significant periods on the coldest mornings. Such climate stress may reduce the ability of the seagrass to recover from the impacts of pollution and other disturbances caused by human activities. Seagrass coverage in the Big Bend Coast may be decreasing. One study estimated that of seagrass beds had been lost off the mouth of the Fenholloway River because of pollution from pulp mill discharge. Other areas, such as around the mouth of the Suwannee River, the southern end of Suwannee Sound near Cedar Key, and Wacassassa Bay, which were reported to have beds of seagrass in the past, do not have them today. Extensive seagrass beds around Anclote Key, at the southern end of the Big Bend Coast, disappeared in the early 1960s.