The Cape San Blas Ecological Study

Principal Investigators: Margaret M. Lamont, H. Franklin Percival, Leonard G. Pearlstine, Sheila V. Colwell, Wiley M. Kitchens, and Raymond R. Carthy

Funded By: The Department of Defense, Eglin Air Force Base, Natural Resources Branch

Introduction


Cape San Blas, Florida lies on the St. Joseph Peninula, part of a dynamic barrier island chain that extends along the northern Gulf of Mexico. Due to the natural forces that formed Cape San Blas, and those that maintain this area, St. Joseph Peninsula has experienced severe landform change over time. These changes allow for fluctuations in habitat types along Cape San Blas that influence the floral and faunal species using this area. The dynamic envronment along Cape San Blas includes flatwoods, interdunal swale, rosemary scrub, and beachfront. These habitats support a wide array of species, including several threatened and endangered species such as the loggerhead sea turtle (Caretta caretta), Piping Plover (Charadrius melodus), Least Tern (Sterna antillarum), and Bald Eagle (Haliaetus leucocephalus). In additon to threatened and endangered species, Cape San Blas supports tourists and recreationists. Although Gulf County is sparsely populated, with approximately 13,000 inhabitants throughout 580 square miles, summer tourism and heavy recreational use of beaches for fishing, crabbing, and shelling place continued and increasing pressure on the natural resources of these areas. Gulf County is also one of the few remaining counties in Florida that permits vehicular traffic on its beaches, including Cape San Blas. To allow continued public use of this area while also protecting the unique flora and fauna of this property, a complete inventory of the physical features of the area was undertaken along with a description of the distribution of selected faunal species. Comprehensive investigation of this area allows for understanding the relationshps among factors influencing Cape San Blas. Each aspect of the environment influences the entire system, therefore all aspects must be researched before successful management is possible.

Erosion

Photo: Jack Cox

Formation and maintenance of barrier islands require abundant sand supplies. Since present sea level has stabilized in the past 4,000 to 5,000 years, there has been very lttle new sand added to barrier islands along the northern Gulf of Mexico. The result is that portions of these barrier islands are being eroded by several forces, including winds, tides, and waves. Erosion influences most barrier islands, although those along the Florida panhandle experience especially large rates of erosion. Historically, the western shore of Cape San Blas has eroded at approximately 11m/yr, with the tip of the St. Joseph Peninsula and the eastern shore of Cape San Blas undergoing accretion. Results of this study support the theory that Cape San Blas experiences one of the greatest erosional rate in Florida. During three weeks in June 1994, the cape spit lost approximately 20m of beach. The north beach also underwent erosion with a net loss of nearly 10m from 1994 to 1995. The east beach, however, accreted nearly 6m throughout the study period. It is apparent from this research that the pattern of accretion and erosion that influences Cape San Blas is the result of natural forces. Vehicular traffic along these beaches may exacerbate the situation, however ocean currents throughout the Atlantic Basin and Gulf of Mexico, wind patterns over the gulf, and changes in sea level appear to be the primary causes of barrier island dynamics along Cape San Blas.


Above is a graph of beach profiles conducted along the north coast of Cape San Blas from June 1994 to September 1995. Each line represents a horizontal profile of the beach during one survey. The red line on the right (with the arrow) indicates the beach profile when the project began, and the dark blue line on the left (with the arrow) shows the beach profile after 15 months. This graph demonstrates the large amounts of sand lost on the north beach of Cape San Blas, and also shows how variable the beach is throughout the year.

Landform and Landcover Change


Cape San Blas has experienced land form change for over 100 years. These changes occur primarily due to natural forces and may be exacerbated by human distrubances.

Sets of aerial diapositives of the St. Joseph Peninsula were obtained for 1942, 1959, 1967, 1971, 1977, 1981, 1990, and 1994. Each set of photography were photogrammetrically scanned. Adjacent images were digitally mosaiked using common image identifiable points, and then georeferenced to a common coordinate system (universal Transverse Mercator; UTM).

To create the digital vector layers, the georeferenced images were used as base maps for photointerpretation and on-screen digitization. Polygons delineating the land cover and landform of Cape San Blas and St. Joseph Peninsula were labeled and attributed interactively and were then compared visually to locations of landscape feature evident on the imagery. Relative accuracy of land cover delineation is estimated to less than five meters for all line work. Image processing steps were performed using ERDAS Imagine 8.2. Vector layers were created using ESRI SRC/Edit GIS software.

Topography of EAFB on Cape San Blas was measured using standard topographic techniques. Conventional survey techniques were employed with the resulting traverses tied to established monuments. Only one Department of Natural Resources (DNR) monument recovered from Hurricane Opal (Octover 4, 1995) was usable, therefore National Geodetic Survey (NGS) monuments were used. Each traverse started and ended at points of known location or looped back. The resulting errors were measured. These errors were assumed to have been uniformly accumulated and the corrections were applied accordingly. Data from this survey was transformed to a continuous spatial surface in Arc/Info and Microstation.

Maps produced in GIS indicate Cape San Blas has undergone landform change since 1942 and support historical data collected in this area by various other researchers.

Hydrology

Tidal patterns were recorded using a Hydrolab DataSonde3 water monitor. This device was attached to an old lighthouse base (the old lighthouse base was toppled during Hurricane Earl in September 1998) that was located approximately 25 yards offshore of the Coast Guard Station on Cape San Blas. The monitor would datalog tidal heights for a given period of time. We would then retrieve the equipment, download the data to a computer, and deploy the monitor again to collect more information.

The water table level plays a large part in defining the habitat type. In some of these habitats, the water surfaces are continuous with those of nearby lakes and swamps, and although they fluctuate with rainfall, they are usually present at some depth. In others, however, water tables are located above clay layers and last only as long as rainfall exceeds losses. Losses are most often due to evapotranspiration, therefore destruction of the green canopy by fire, wind, or logging often temporarily increases the height and duration of both types of water tables. Therefore, habitat type is determined in part by the depth and stability of the water table.

The Florida Aquifer is the most important freshwater aquifer in Florida, underlying much of the central and eastern panhandle, and most of the peninsula of Florida. This is the thickest and most productive unit in the central panhandle, supplying the bulk of the domestic, urban and agricultural water used in Gulf County. The top of the aquifer varies in depth from approximately 150 MSL at the northern edge of the county to 500 ft MSL under the St. Joseph Peninsula, including Cape San Blas. The Floridan aquifer system is confined in all areas of Gulf County. Most water flowing through the Floridan aquifer system is discharged into the Gulf of Mexico.

During this project, water sampled in freshwater wells throughout all habitats on Cape San Blas was taken from the surficial aquifer system. Changes in depths and salinities were consistent with the characteristics of this aquifer. Water table depths varied among habitats, most likely due to differences in the surface topography and rainfall. Salt water intrusion into the surficial water table may alter the habitats dependent on the water table for survival. Several plant species, particularly those comprising mangrove habitats, are able to survive saltwater intrusion by excluding or excreting salt. Hardwood hammocks, however, are less able to survive salt water inundation, therefore these species are restricted to freshwater uptake. Changes in the salinity of the surficial water table may, therefore, greatly influence the plant species inhabiting the area.

Tides may also contribute to saltwater intrustion, although along Cape San Blas this does not appear to be so. Tides effect this area in a different way, however. The amount of damage afflicted by a tropical storm is often exacerbated by the tidal range and water depth offshore of the site where the hurricane strikes land. Tidal ranges vary throughout Florida. Because the northern Gulf of Mexico is shallow and relatively flat, wave action is slight which allows for smaller tidal ranges observed along the Gulf of Mexico coast. Therefore, the small tidal range that occurred along Port St. Joe during our study is typical of the panhandle coast, whereas the tidal range off Cape San Blas was even narrower than the average ranges along the northwest Florida coast. Small tidal ranges may increase risk for severe damage during storms because they do not provide buffers for storm surges. The narrow tidal range along Cape San Blas may not provide a sufficient buffer during tropical storms, therefore, this area may experience severe damage during storm events.

Soils

Often, changes in vegetation types occur across major soil boundaries, therefore identifying soils types may aid in understanding the various vegetative habitats located in an area. The soil types located along Cape San Blas are most likely influenced by the source material of this barrier island and the water table supplying the soils with nutrients.

Soil samples were collected by personnel in the Soil and Water Science Department at the University of Florida during 1995 and 1996. Soils were collected from the surface to maximum depths in each major horizon and subhorizon, and subsamples were taken within horizons that were more than 50 cm thick.

The results of particle size analyses indicated all the soils sampled along Cape San Blas were high in sand content with just a very small amount of silt and clay. The fine sand size fraction dominated the sands, with the exception of one map unit that contained medium sand in most of the horizons. In addition, the frequently flooded unit contained a higher percentage of coarse sand than the other soils sampled. These differences in sand sizes may reflect the effects of the frequent flooding and rapid water movement. The other soils sampled generally had a very low content of coarse sand as well as a very low content of very coarse sand and very fine sand. The dominance of the fine and medium sand sizes may indicate a uniform rate of depositions of the sandy sediments.

Birds

Neo-tropical Birds

Migrating birds are often exhausted and energy-depleted after crossing large barriers, such as the Gulf of Mexico. Therefore, peninulas and barrier islands become natural funnels for migrating birds. Cape San Blas provides a variety of habitats for neotropical migrants, including ridges of rosemary scrub and swales of slash pine. In addition, of the approximately 500 acres of property managed by Eglin Air Force Base on Cape San Blas, only about 100 acres are occupied and the remaining are undeveloped.

Red-eyed Vireo (Vireo olivaceous)
Hooded Warbler (Wilsonia citrina)

Transient neotropical migrants require more than just appropriate habitat and undeveloped tracts of land, however. During this study, fewer than 10 transient neotropical migrant species were recorded during fall 1994 and spring 1995 migrations. Although nearly 2,000 individual birds of nearly 60 species were recorded in fall, and slightly greater than 2,000 birds of nearly 70 species were recorded in spring 1995, the majority of these birds were resident species, such as the Rufous-sided Towhee (Pipilo erythrophthalmus) and the Northern Cardinal (Cardinalis cardinalis). It is possible that this area is lacking suitable food resources or protection from predators. In addition, weather patterns over the Gulf of Mexico during spring and fall migration may carry birds further west causing them to travel primarily along the central flyway over Texas.

Wading Birds

The large amount of coastline and significant areas of wetlands found in Florida support a large number of wading bird species. Along Florida's gulf coast, Reddish Egrets (Egretta rufescens), Snowy Egrets (Egretta thula), Tricolored Herons (Egretta tricolor), and Yellow-crowned Night Herons (Nycticorax violaceus) breed. Much of these breeding areas in South Florida have been developed, thus destroying wading bird breeding habitat. The northwest coast of Florida has yet to undergo the amount of development that has influenced south Florida, therefore providing pristine habitat for wading birds.

Great Egret (Casmerodius alba)
Great Blue Heron (Ardea herodius)

Wading birds were observed in small yet consistent numbers from April 1994 through April 1996 along Cape San Blas. The most common species were the Great Egret, Snowy Egret, and Great Blue Heron, which are all permanent residents of Florida. Great Egrets are the most cosmopolitan of all heron species, and their range is still expanding following severe depletion by plume hunters at the beginning of the century. The Snowy Egret's range also continues to expand. This highly colonial species is often found in mixed flocks throughout the state. The Great Blue Heron is a common species throughout the United States and numbers of this species are increasing throughout its range. The fourth most common species found along Cape San Blas was, however, a less common and abundant species. The Reddish Egret was hunted extensively in the early 1900's and disappeared from Florida from 1927 to 1937. Presently there are approximately 2,000 breeding pairs throughout the United States and about 400 breeding pairs in Florida. Along Cape San Blas, Reddish Egrets were observed in small numbers during every season throughout the study period. These individuals were most likely immature birds wandering during post-breeding dispersal. It may be possible, however, that the range of the Reddish Egret is expanding, and may soon include Cape San Blas.

Shore Birds

The Texas coast is often considered one of the primary flyways for migrating shorebirds. These species are often found feeding along the coastal beaches and barrier islands of Texas. These systems are dynamic however, and subject to disturbance, such as erosion, human influence, and hurricanes. In addition, competition among shorebirds along these beaches may limit the number of birds using this area. Therefore, migrating shorebirds may have secondary areas utilized when primary habitat is unavailable or when individuals are unable to compete for primary sites. Cape San Blas may provide such a site for migrating shorebirds.

Dunlin (Calidris alpina)
Sanderling (Calidris alba)

Nearly 8,000 shorebirds of approximately 30 species were observed along Cape San Blas from April 1994 through April 1996. The greatest number of shorebirds and shorebird species were recorded in spring. The most common species observed in this area was the Sanderling, with the Willet (Catoptrophorus semipalmatus) accounting for the second most common. Another common species observed along Cape San Blas was the federally threatened Piping Plover (Charadrius melodus), which was observed throughout the year. Although past surveys indicated the Florida coast may not represent a significant wintering area for Piping Plovers, it appears Cape San Blas supports a consistent number of Piping Plovers. This species may exhibit great sight fidelity, therefore once plovers begin using Cape San Blas, they may continue to return in future winters.

Sea Birds

The Gulf of Mexico coastline supports significant nesting populations of gulls and terns. Approximately 95% of the United States breeding population of Sandwich Terns (Sterna sandvicensis), 70% of the Black Skimmers, and 60% of the Forster's Terns nest along the Gulf of Mexico coast. Many seabird species are year-round residents of the Gulf coast, however numbers typically increase as migrants move south from additional northern breeding grounds. Because the beaches and barrier islands that seabirds rely on are often altered by hurricanes and coastal erosion, these species must be able to relocate after a disturbance. Species relocating due to disturbances along primary breeding and roosting areas in Texas and Louisiana may utilize the habitats along Cape San Blas.

Photo: Erin McMichael
Black Skimmer (Rynchops niger)

During this study we observed slightly greatly than 31,000 seabirds of 17 different species along Cape San Blas, which indicated this area may represent significant habitat for seabirds. The most common species observed during this study were the Royal Tern, Laughing Gull, and Brown Pelican. These common residents of the Gulf of Mexico coast tend to nest and roost in large, mixed congregations along sandy beaches, and marshes. This area provides both marsh and sandy beach habitat, with direct access to the Gulf of Mexico for foraging. The Cape spit is typically available at low and high tide and provides resting areas for all seabirds, especially fledging Brown Pelicans that are unable to land in trees where adults nest. Cape San Blas is significantly impacted by erosion and human disturbance, however, and will require continued monitoring and protection for sustained use by seabirds.

Beach Mice

The oldfield mouse (Peromyscus polionotus) is common and abundant throughout the southeastern United States. Along the Atlantic Ocean and Gulf of Mexico coasts, local populations of the oldfield mouse, known as beach mice, have been isolated by formation of islands and rising sea levels and have diverged into separate subspecies. One species of beach mouse currently protected by Florida as an endangered species and under consideration for federal listing is the St. Andrews beach mouse, P. p. peninsularis.

The historic range of the St. Andrews beach mouse was Crooked Island (Bay County), south and east to the St. Joseph Peninsula (Gulf County). It is unknown, however, if beach mice still inhabit this entire range. St. Andrews beach mice typically occur in well-developed dunes where the major vegetation is sea oats. They also inhabit older and higher back dunes that support live oaks and rosemary. In October 1995, Hurricane Opal struck the Florida panhandle and destroyed most of the dunes along Cape San Blas. It is unknown if Cape San Blas supported a population of St. Andrews beach mice prior to Hurricane Opal and if so, how this natural disturbance affected the beach mice in this area.

Our data indicated Cape San Blas does not support a population of St. Andrews beach mice. Possibly, due to habitat destruction or increased numbers of predators, the range of this beach mouse has decreased. Habitat destruction may occur due to natural distrubances such as hurricanes or human disturbances, including beach driving.

Cape San Blas has been severely impacted by several storms, including Hurricane Agnes in 1972 that had sustained winds of 86 mph and a 7 ft tidal surge, Hurricane Elena in 1985 during which 1,500 ft were lost from the cape point along Cape San Blas, and Hurricane Kate in 1985 that had sustained winds of 135 mph and a tidal surge of 8 ft.

On Eglin Air Force Base, commercial and residential development are not permitted, therefore human development of beach mouse habitat along Cape San Blas may not be restricting mice from inhabiting this area. Although development is not permitted along Cape San Blas beaches, vehicular and foot traffic are allowed. Species of dune vegetation, such as sea oats, may be influenced by vehicular traffic. Therefore, even if vehicles on Cape San Blas are not driving directly over dunes, they may be limiting colonization of dune vegetation, thereby preventing formation and growth of dunes. Lack of dunes along Cape San Blas would most likely result in poor habitat for St. Andrews beach mice.

Storms

Hurricane Erin's time-lapse path: September 1995
Effects of Hurricane Earl: September 1998

Climate directly affects an area by influencing the weather and environmental conditions, either through persistent, long-term weather patterns or through occasional, short-term events. Weather patterns influence the type of habitat and fauna that inhabit by providing sun, rain, high or low temperatures, and humidity. In some areas however, occasional short-term climatic events, such as tropical storms, may cause extreme damage. In the United States, tropical storms primarily affect the Southeast. From 1971 to 1992, nearly 1,000 tropical storms have occurred in the tropical north Atlantic Ocean, with about 180 of those having struck or passed immediately offshore of the Florida coastline.

Because South Florida is more developed than Northwest Florida, severe storms in South Florida typically cause more economic damage. Although South Florida may experience greater economic damage than the panhandle during a hurricane, Northwest Florida experiences greater storm surges due to the shallow waters along it's coast, thus resulting in increased severity of storms that affect this area. The average minimum pressure in Florida's hurricanes is 50mm less than the average atmoshperic pressure. ths amounts to a lifitng of approximately 0.5m, of water. Near shore, however, this may result in a mound of water as high was 4 m. Because of the action of waves, the surge of water may even be greater if the hurricane approaches shore rapidly. Furthermore, coastal areas with a greater extent of shoaling will generally expreience a higher storm surge. Therefore, in hurricanes of equal size and strength, the Gulf coast of Florida typically experiences greater storm surges than the Atlantic coast. hs results in extreme alterations to the coastlne and habitat along the Florida panhandle. Because waters off Cape San Blas are shallow and shoal extensively, storm surges caused by tropical storms are often large and cause significant damage to structures and habitats.