The dune fields of the panhandle barrier islands closely mimic those in the deserts of the American southwest. With rolling hills of sand (less the rock), small, spaced shrubs, and high temperatures, hiking through the dunes reminds me a lot of hiking the deserts and canyonlands out west. Oh… and you rarely see wildlife in both habitats.
There are many forms of wildlife that are very hard to find in our area. But we continue to look.
Photo: Rick O’Connor
It’s not that wildlife is not present, its just not visible – and this would be true for both habitats. These systems are more open, easier to spot predator and prey, and the temperatures can be extreme. Because of this the animals who reside here are more active at other times of the day and we are made aware of their presence by tracks or scat.
The deserts of the American southwest are ecologically very similar to the dunes of barrier islands.
Photo: Rick O’Connor
In winter the temperatures in the dunes can get quite cold. Being in the eastern United States, and closer to the warm Gulf Stream, the atmosphere is more humid and cold temperatures can feel even colder – the “wet chill” everyone talks about. Add to this the winds from the north and it can be an unpleasant place to be out and about. Many plants have gone dormant not producing flowers or seed, and the leaves falling or shriveled and brown, and you have very little for the herbivores to feed on. When conditions get like this animals have basically two options. One, hunker down, hibernate, wait for conditions and food sources to improve. Two, leave – head south where conditions are more favorable. Either way, you do not see them.
A hike in winter finds little wildlife moving about. Birds are common. Many have flown south from harsher conditions further north and seem to enjoy being out. Unless it is unseasonably cold and windy, you can find a variety of passerines (songbirds) in the shrubs and bushes of the dunes. Mockingbirds, cardinals, and mourning doves are often seen. There are also unique species more common up north. Christmas time is a popular time for the Audubon Society to conduct their annual bird counts. Many volunteers often log species rarely seen during other times of the year.
Mockingbirds are a common passerine bird found on barrier islands. Photo: Rick O’Connor
Mammals and reptiles are not often seen during the daylight hours. Some reptiles may come out of hiding on days when the sun is bright, and the winds are low. They will find a windbreak near a dune and bask in this sunlight for a few hours. But to see them it is one of those “being in the right place and the right time”. Daytime is short this time of year and they are not out very long.
Mammals being endothermic can move around. They are still not frequently seen during the daylight hours because the habitat is too open and hunting not as successful. There are also a lot of humans on our islands now and many mammals are not fond of this and tend to avoid us. So, they change their pattern of activity to other times. Animals who are active during the daytime are called diurnal. Those more active at night are nocturnal. And those more active at dawn and dusk are called crepuscular. During the winter many mammals tend to be more crepuscular because the evenings can get quite cold no matter what the wind is doing. If they are not hibernating, they will hunt for a few hours at dawn or dusk and then hide during the colder parts of the evenings.
During my winter hikes I have seen primarily passerine birds, and occasionally an armadillo. But most sign of wildlife are the tracks of raccoons, coyote, and deer.
Raccoons are common all over the island.
In the spring things change. The earth is tilting more towards the sun, the days become longer, and the cold air masses are met by the more tropical warmer ones. Temperatures and rainfall increases. These warmer temperatures are more inviting to daytime foraging for prey. Ephemeral ponds form due to the increase rainfall. Island amphibians take advantage of this mating and laying their non-cledoic eggs in these ponds while they are still there. The warmer evenings are filled the calls of male frogs seeking females. Mammals are still more crepuscular and nocturnal, but it is a time when your chances of spotting one during the daylight hours increases. Not only is the weather better but the food sources are as well, and some have been hibernating for a couple of months and are quite hungry. Hunger will push them to be more active during daylight than they would otherwise be. The same can be said for reptiles. Snakes moving during daylight is more common this time of year.
Freshwater ephemeral pond.
This is also the time for mating. It will be warm for several more months and this is the best time to raise a small offspring. The temperatures are warmer (conducive to growth), food more abundant (needed for growth), and you avoid the colder temperatures that can kill small animals. Males of these species are out and about seeking females and defending territories. Nesting birds of several varieties can be found building such nests. Turtles and snakes are breeding and seeking good locations to lay their eggs. With all of this comes more activity and more encounters by human hikers.
Let’s not forget the insects. Actually, you can find these creatures at all times of the day in all seasons. Insects are one of the most resilient groups of animals on the planet, and their high diversity – even on barrier islands – supports this. In the spring when the rains come and the ephemeral ponds are available, insects begin to breed and fill the skies. Spring is a very active time in the dunes.
This tick was a hitchhiker on our trip through the dunes.
Photo: Molly O’Connor
Summer brings the heat – particularly late summer. Like the deserts of the southwest, temperatures can rise above 100°F and it is not the best time to be out and about. Much of the wildlife becomes more crepuscular or nocturnal. I have noticed when doing snake surveys, that the snakes may be moving at dawn but by 8:00-9:00am, when you begin to feel the heat of the day, you find no more. They have moved to the shade or a burrow somewhere. BUT the lizards begin to move. Lizards are a popular food for snakes, and it makes sense they would be more active when snakes are not. However, the sand is hot, and birds are also predators. So, lizards, like the six lined skink (Aspidoscelis), move VERY fast across the hot sand from one bush to another. I even notice the passerine birds becoming less common as the heat increases – it is hot out there. Interestingly human activity seems to increase when the temperatures are at their highest. We tend to sleep later than most animals this time of year.
This straight line the sign of a tail drag by a lizard, most likely the six-lined skink.
The fall brings some relief from the heat. As the earth begins to tilt away from the sun and the days become shorter, the temperatures begin to drop, and it is more comfortable coming out during daylight hours. Humans are still around so many will still avoid daylight but it also a time to prepare for winter. Seeking food resources and eating as much as possible is the rule for many. For some it is also a time for breeding. Carrying for offspring in a den or burrow over winter is an option for some species. Because of this they are out seeking mates and may be seen during daylight hours when doing so. This would include some of the snakes like the eastern diamondback rattle snake (Crotalus) and the cottonmouth (Agkistrodon).
Coyote seen on Pensacola Beach.
Photo: Kristen Marks
Though dunes seem void of wildlife there are actually many species that reside here and even more than transient there from other parts of the island. Hikes through the dunes can bring magnificent sunrises and sunsets, just as you see in the deserts out west, and – if you are there at the right time and not moving too much – some really neat wildlife encounters can occur. But further back on the island exist the maritime forest. Here there are more creatures and more encounters. This will be the focus of Part 6.
The open sandy beach is one of the hardest habitats to live in on a barrier island. There is no where to hide and almost nothing to eat. Add to this the direct wind and waves from the Gulf of Mexico and you have a barren landscape with continuous climate and ocean energy. But creatures do live here.
The beach is void of plant life and takes a well adapted animal to reside here.
Phot: Rick O’Connor
Before we go further let’s define a few terms. The beach is actually the dry sandy portion of this environment. The area where the sand squeaks as you walk through it, the place where you set your chairs, umbrellas, and lunch for your day at the beach. The berm is the harder packed sand near the waters edge. The place where you like walk when you walk the beach (it’s easier) and the waves wash over every few seconds. Living in these two would be very different. Second, we will define resident and transient. A resident is a creature who actually resides there. A transient is just passing through but lives somewhere else.
As you look across the beach you will notice there is NO WHERE to hide from the elements… except beneath the sand. One of the more common creatures who lives beneath the is the ghost crab (Ocypode quadrata). This crustacean digs burrows down to the water table where they can keep their gills wet and this can be as deep as four feet. On these flat beaches they are easy target for predators. They have several ways to deal with the problem. (1) Their compound eyes are on stalks above their head to give them a wider, and longer, range of view. (2) They are white in color and blend in with the quartz sand well. (3) They are more active at night, nocturnal. (4) They are very fast.
The trick to speed is to break contact with the ground. If you were to ask someone “what is the fastest way to get to Los Angeles?” They would answer “flying”, and this would be correct. Birds are some of the fastest creatures around. They fly. They lift off the ground and do not touch again until they reach their destination. It does not get any better than that. Cheetahs are very fast as well. But if you watch them in slow motion, you will see they are basically leaping from one point to the next. They touch the ground very few times over a certain distance. They are trying to fly but cannot. If look at video of a human, or centipede, or slug. Not sot good. Crabs are crustaceans and by definition they have 10 legs. When they move across the surface, they usually use eight of those (two being their claws). The same is true for the ghost crabs. But when they decide to run, they only run on three of them. They raise the other five above their heads. This means fewer legs touching the sand which means they are faster.
The common ghost crab. Photo: Virginia Institute of Marine Sciences
Food is another issue. Due to direct high wind (filled with salt), plants do not grow on the beach. Hence the classic food chain (plant – herbivore – carnivore) cannot exist. So, what do ghost crabs eat? They are scavengers. They emerge from their burrows, usually at night, to seek what dead creatures the tide may have washed in. Post storms are particularly good feeding times. Surf fishermen along the Gulf beach often catch hardhead catfish and, not liking them, often toss them on the beach to die. In the evening the ghost crabs will drag these to the entrance of their burrows where they feast for quite a while. They eventually clean to fish to the bone leaving their “hard head” (the skull). When you look at the skull from underneath it appears to be Jesus on the crucifix. These skulls are often collected and sold in novelty stores as “crucifix fish”.
The bones in the skull of the hardhead catfish resemble the crucifixion of Christ and are sold as “crucifix fish”.
Photo: Rick O’Connor
Another prize for ghost crabs are sea turtle eggs. Sea turtles are obvious transients to the beach environment, coming here only during nesting season. The females usually approach the beach close to where they were born at night. She will labor her way across the beach to the first dune line, though some will lay theirs in the open beach area. She could spend several hours digging a hole three to five feet deep. Loggerhead Sea Turtles (the most common on our beaches) simply dig a hole. The Green Sea Turtle will use her flippers to dig a form for her body before digging the nest. She will deposit about 100 eggs before burying them and returning to the Gulf. Ghost crabs, and other beach transients like coyotes, fox, and raccoons, will find and raid these nests.
Tracks left by a nesting Green Sea Turtle. Courtesy of Gulf Islands National Seashore.
The wrack (a line of debris that includes seaweed, shells, and other flotsam from the Gulf) offers a variety of food for ghost crabs. Another who is often found scavenging the wrack are shore birds. There are numerous species of terns, gulls, pipers, and plovers that will pick through the wrack for food.
The berm is a tougher place to make home. You are in the surf zone and must deal with breaking waves every few seconds. As you might expect, there are no plants here, and very few animals. Those that do reside here bury in the sand knowing that the surf will most likely expose them and could carry them to another location. The two most common animals in this zone are the mole crab and the coquina.
The mole crab is often called a “sand flea”.
Photo: Rick O’Connor
The mole crab (Emerita talpoida) is also known by surf fishermen as the “sand flea”. It is a small oval shaped crab that has a hard paddle like telson to dig into the wet sand tail first. With its head exposed it will extend antenna that are covered with small hair-like structures designed to collect plankton from the water that covers it when the waves come in. The surf often exposes them, but they flip over and dig back in very quickly.
The coquina (Donax variabilis) is a small clam that comes in a variety of colors (hence it’s species name). Like all clams, it has a fleshy foot which it uses to quickly dig into the wet sand covering most of its body. Like the mole crab, it exposes its head into the surf extending two fleshy tubes called siphons that draw water into the clam where it can collect planktonic food.
Coquina are a common burrowing clam found along our beaches.
Photo: Flickr
Predators do exist here, but they are not residents. They would include transient fish that come close to shore waiting for the surf to wash these small animals into the Gulf. One of the more common is the Florida Pompano. Surf fishermen like to use “sand flea” baskets, dragging them through the sand near the waters edge to capture the mole crabs for bait seeking these tasty fish. Others would include an assortment of shorebirds like sand pipers and plovers who run to the wet sand when the surf recedes back into the Gulf probing for the mole crabs and coquina, then quickly running back towards the beach when the surf returns.
A variety of shorebirds utilize the wrack. Photo: Rick O’Connor
The diversity of life in the beach-berm zone is not high, but this is a tough place to make a living. Ghost crabs, mole crabs, and coquina clams have all adapted to living here and have done quite well. But more wildlife prefers the dunes. It is a little easier there and the next stop in Part 5 of this series.
Historically the average rainfall in the Pensacola Bay is around 60 inches per year. However, over the past 10 years that has increased to slightly more than 75 inches per year (see Table 1). The frequency of those levels over the past decade shows that most are between 60 – 80 inches but there have been two years with over 90 inches reported. In the last decade, nine of the 10 years had total rainfall above the historic mean for the area.
Along with the increase in rainfall has come an increase in development. This increase reduces the amount of the excess rainfall to percolate into the ground and recharge our aquifer. Instead, it is directed into stormwater projects to reduce flooding in the community. Some of this stormwater will eventually find its way to the estuary or the tributaries that feed the estuary. The question is whether this increase in freshwater run-off is enough to decrease the salinity of the bay system.
There are several restoration projects ongoing within the bay. Two of them Sea Grant has been involved in. One is monitoring the status of seagrass and the other is status of bay scallops. The species of seagrass in lower bay, such as turtle grass (Thalassia testudnium) and shoal grass (Halodule wrightii) require salinities to be at, or above, 20 parts per thousand. Bay scallops depend on turtle grass for their life cycle and also require the salinity at, or above, 20 ppt.
Citizen volunteers are assisting Florida Sea Grant by monitoring the salinity of the bay on a weekly basis.
Volunteers are trained to use a refractometer and asked to monitor their assigned beach once a week, reporting their results to Sea Grant and calibrating their instrument once a month.
We are asking our volunteers to continue to monitor until they have logged 100 readings.
Currently 21 locations around the bay are being monitored. Nine are in the Big Lagoon area, eight near downtown Pensacola, and four near Pensacola Beach.
12 of these sites are actively being monitored at this time, 3 have reached the 100-reading mark, and 6 have not been monitored in some time.
Note:
Our volunteers are monitoring the water at the surface near the beach due to ease of access. The seagrass and scallops we are interested in grow at the bottom and at depth. However, saline water is more dense than fresh, and it is assumed that the water on the bottom at depth is saltier than the data being found at the surface near the beach.
There are other agencies who are monitoring salinity at depth.
Data for Each Site as of the end of 2022
Table 3 – Salinity Mean, Median, and Mode from Around the Pensacola Bay Area
Water Body
No. of samples logged
Mean
Median
Mode
Bayou Chico
7
10
5
5
Bayou Grande
29
20
21
21
Bayou Texar
10
8
7
ND
Big Lagoon
15
23
20
20
Big Lagoon SP
51
16
15
14
Big Sabine
64
22
22
22
Bruce Beach
1
18
18
ND
Ft. McRee
4
21
21
19
Galvez Landing
65
22
23
22
Hawkshaw
24
16
15
15
Kees Bayou
100
20
21
14
Little Sabine
100
23
23
25
Lower Perdido Bay
100
16
15
20
Navy Point SE
21
17
17
20
Navy Point SW
22
16
17
10
Old River
36
23
23
25
Oriole Beach
51
25
25
25
Perdido Key SP
33
21
20
15
Sanders Beach
70
18
18
18
Siguenza Cove
11
22
21
21
Shoreline Park
10
25
25
25
TOTAL
824
19
19
19
Table 4 – Salinity Mean, Median, and Mode from the Big Lagoon Area
Water Body
No. of samples logged
Mean
Median
Mode
Big Lagoon
15
23
20
20
Big Lagoon SP
51
16
15
14
Ft. McRee
4
21
21
19
Galvez Landing
65
22
23
22
Kees Bayou
100
20
21
14
Lower Perdido Bay
100
16
15
20
Old River
36
23
23
25
Perdido Key SP
33
21
20
15
Siguenza Cove
11
22
21
21
TOTAL
415
20
20
19
Table 5 – Salinity Mean, Median, and Mode for the Downtown Pensacola Area
Water Body
No. of samples logged
Mean
Median
Mode
Bayou Chico
7
10
5
5
Bayou Grande
29
20
21
21
Bayou Texar
10
8
7
ND
Bruce Beach
1
18
18
ND
Hawkshaw
24
16
15
15
Navy Point SE
21
17
17
20
Navy Point SW
22
16
17
10
Sanders Beach
70
18
18
18
TOTAL
184
15
15
15
Table 6 – Salinity Mean, Median, Mode for the Pensacola Beach Area
Water Body
No. of samples logged
Mean
Median
Mode
Big Sabine
64
22
22
22
Little Sabine
100
23
23
25
Oriole Beach
51
25
25
25
Shoreline Park
10
25
25
25
TOTAL
225
24
24
24
Discussion
A glance at Table 3 will show all 21 bodies of water that have been involved in this project. Three of those, Lower Perdido Bay, Kees Bayou, and Little Sabine have reached the 100-reading mark.
For Lower Perdido Bay the mean salinity was 16 ppt ±5. The highest reading was 24 ppt and the lowest was 6 ppt. The median was 15 ppt and the mode was 20. These data suggest that this body of water would not support turtle grass or bay scallops, but it is not believed that historically lower Perdido Bay did. We would like to thank Bob Jackson for his effort on collecting these data.
For Kees Bayou the mean salinity was 20 ppt ±6. The highest reading was 31 ppt and the lowest was 5 ppt. The median was 21 ppt and the mode was 14 ppt. These data suggest that turtle grass and bay scallops could survive here. It is noted that Kees Bayou is a shallow basin located next to a highway and during intense rainfall the salinities could drop drastically to cause a decline of both target species. We would like to thank Marty Goodman for his effort on collecting these data.
For Little Sabine the mean salinity was 23 ppt ±4. The highest reading was 30 ppt and the lowest was 12 ppt. The median was 23 ppt and the mode was 25 ppt. These data also suggest that both turtle grass and scallops could survive in Little Sabine, and there are records that scallops were once there. Turtle grass exist there now. We would like to thank Betsy Walker and Liz Hewson for their efforts on collecting these data.
The Big Lagoon Area
These data suggest that most of the sampled areas could, in fact, support both turtle grass and scallops, and there are records that they have supported both in relatively recent years. One note of interest is the lower salinities near Big Lagoon State Park. Most of the sites have data at 20 ppt or higher – except Lower Perdido Bay (understandable) but we are not sure why the numbers are below 20 ppt. at the state park. We would like to thank our active volunteers in the Big Lagoon area Jessica Bickell, Glenn Conrad, John Williams, and Emogene Johnson for their effort in collecting these data.
The Downtown Pensacola Area
These data suggest that this area of the bay would not support turtle grass nor bay scallops. But historically they did not. Seagrass does exist in these bodies of water but much of it is widgeon grass (Ruppia maritima) which can tolerate lower salinities. We would like to thank our active volunteers for the downtown area Tim Richardson and Glenn Conrad for their efforts in collecting these data.
The Pensacola Beach Area
These data suggest that Santa Rosa Sound could support, and do support, populations of turtle grass and scallops. During our scallop searches conducted in July we have found one live scallop in Big Lagoon and two in Santa Rosa Sound over the last six years. Again, these data suggests that all of these locations could do so with the highest salinities in the bay area based on these data. We would like to thank our active volunteers in the Pensacola Beach area Ann Livingston, Gina and Ingo Hertz, and Holly Forrester for their efforts in collecting these data.
Though we have not reached the targeted 100-readings for most of our sites, these early results suggest the rainfall may not be lowering the salinity. We will continue to monitor until we do reach the 100-reading for each and have a better idea.
We are seeking new volunteers. The water bodies needing help are Bayou Chico, Bayou Texar, Big Lagoon, Bruce Beach, and Sanders Beach. If you are interested contact me at roc1@ufl.edu
The classic model of ecological succession begins with new land. This could be new land formed by a sand bar, or a new landscape formed after a volcanic eruption, but new land none the less. Then the pioneer community begins. Based on the model, the plants need to be first, herbivores cannot survive unless there are plants already present. When we teach students about maintaining aquaria, we actually begin with the bacteria community needed to breakdown the organic waste from the plants and animals when they arrive. So, some would say “begin there”. As the pioneer plant communities form, the pioneer herbivores arrive. This would be followed by more advanced communities of plants and then more advanced communities of animals, until you reach the climax community.
Beach
The open beach is how most barrier island ecosystems begin awaiting the arrival of the pioneer community.
Phot: Rick O’Connor
But science understands that it is more complicated than that. Each new member of the community would make chemical and physical changes to the environment that could allow new species to thrive while other existing ones die off. Then those would make changes as well and the process is ALWAYS changing. That there is never a true climax community, change is happening all of the time. Then there was the case of Mt. St. Helens.
St. Helens erupted in 1980 destroying 229 square miles of habitat. This new landscape gave ecologists an opportunity to witness ecological succession firsthand. Like everyone, they expected the pioneer plant community to arrive first, and so on. But in some areas, it was the carnivores that arrived first, completely against the classic model. These carnivores apparently survived the blast and began to wonder the new landscape. How did they survive? They survived by feeding on each other. But eventually the pioneer plants did arrive, all creatures “got in line” and the world was good once again. The interesting thing was it did not happen the way they thought it would. It also shows the resiliency of life.
Mt. St. Helens destroyed almost 300 square miles and produced new habitat.
Photo: University of Washington.
So, how did this process unfold on our barrier islands? I do not know. You would guess that it unfolded the way the model suggests – pioneer plants first, pioneer animals, more complex plants, more complex animals, barrier island ecosystem. But as we have seen, there are several ways it could have started.
What we do know is that the animals who made it to the islands had to do so by either swimming, flying, or walking. For those who reached our islands on foot – beach mice, ants, etc. this must have happened at a time when the island was still connected to the mainland.
The Choctawhatchee Beach Mouse is one of four Florida Panhandle Species classified as endangered or threatened. Beach mice provide important ecological roles promoting the health of our coastal dunes and beaches. Photo provided by Jeff Tabbert
For the swimmers, short swims like Indian Pass could be achieved by several species. Deer and other small mammals may have been able to do this. I have seen bears swim and assume coyotes could make short swims. As the island continued to move with the tide and currents, the distance to the island would have increased. The pass across the mouth of our estuaries, or across the intracoastal waterway, is now daunting for many of these swimmers – but not all. I have seen eastern diamondback rattlesnakes swim across the ICW and have heard bears can still make this trip. For the flyers, these distances do not seem to be an issue. They easily, and often, do so.
Eastern diamondback rattlesnake swimming in intracoastal waterway near Ft. McRee in Pensacola.
Photo: Sue Saffron
If you imagine the early days of an island being low elevated sand, the new wildlife arrivals would face a daunting landscape. Burrowers, such as ghost crabs, could easily make a living here. Their burrows protect them from the elements and being scavengers, they would feed on anything the Gulf washed ashore – something they still do. Sea turtles and shorebirds could easily use the sand bars for nesting, and probably preferred it due to the few predators around. But eventually, the pioneer plants would become more established, allowing selected herbivores (who could survive in low elevation sand) to move in. Next the dunes would form, providing new habitat (read part 2 of this series). Additional herbivores, if they could reach the island, could now become established and at some point, the carnivores would enter the picture.
The line of seaweed and debris along the surf zone is called wrack. Photo: Rick O’Connor
There would initially be a finite amount of space for inhabitation and competition for that space and its resources would be high. Some would be more adapted to the environment than others, or physically stronger, or have a higher reproductive rate, to give them an edge over the others and the island wildlife community would begin. This community would include such things as insects, worms, amphibians, reptiles, birds and mammals. The marsh habitat would include aquatic species such as snails, clams, crabs, shrimp, and fish. All would have had to be able to reach the island, find a suitable habitat for their needs, find suitable food, and out compete others who had made the trip across as well. I was asked once as a college student – “who is a rhinoceros’s greatest competition?” It was an oral exam, and I was very nervous. My mind began reeling in all directions trying to think of what a rhino would have to compete for and WHO would be their greatest competitor. And then, with a little discussion from my professors, it dawned on me. Their greatest competitor would be another rhino. The other rhino would be seeking the same resources, habitat, and mates as the original one. Your first problem is with your own kind. And so, it would be for barrier island wildlife.
The bizarre looking armadillo enjoys a walk on the beach.
Photo: Rick O’Connor
With the arrival of humans, with their bridges and boats, additional creatures would be able to reach the islands and play a role in the competition, but that is another story, and we will discuss this more down the road. In Part 4 we will look at the species that have inhabited the beaches of our barrier islands.
The habitats of a barrier island are defined and driven by the plant communities there. Seeds from the mainland must first reach the new island and they can do so using a variety of different methods. Some come by wind, some by water, some by birds and other wildlife. Some of these germinate, some do not. Those that do, do so on a sandy island with little or no relief and must deal with the winds off the Gulf, which has salt spray. Many of these mainland plants cannot tolerate this and never make it. But some can… and do.
The dune fields of panhandle barrier islands are awesome – so reaching over 50 ft. in height. This one is near the Big Sabine hike (notice white PVC markers).
These early plant communities are known as the pioneer community – meaning the earliest settlers. In the process of succession pioneer communities are made of creatures that can tolerate the harshest conditions, the early days of ecosystem development. There are usually few nutrients, extreme climatic conditions, and for the animals, few prey to select from. But these pioneers are adapted to survive in these conditions and over time alter the conditions so that other creatures can move in.
For the barrier islands, grasses seem to be the plants who do best in the early stages of succession. Though small shrubs and trees may reach the island, the high winds and salt spray will not allow growth. There are numerous species of grasses that can live here, the most famous are the sea oats (Uniola paniculata). This grass can be found on the smallest of barrier islands. Their fibrous root system runs beneath the ground sprouting new grasses all over. Their seed heads blow with the wind starting new populations of plants on other locations and the landscape is soon dominated by them. However, there are other species as well. Panic grass (Panicum amarium), salt hay (Spartina patens), and beach elder (Iva imbricata) to name a few. All these grasses can tolerate the wind and salt spray as well as the low nutrient, low rainfall often found on these islands. They also all have fibrous roots systems that not only connect grasses across the land scape but also trap blowing sand – forming dunes.
The primary dune is dominated by salt tolerant grasses like this sea oat. Photo: Rick O’Connor.
The dunes closest to the Gulf are dominated by grass due to the higher winds and salt spray there. These are called the primary dunes and create one of the first habitats on the island for wildlife. The primary dunes vary in height and how far from the Gulf they range but they do form a wind break for portions of the island landward of the Gulf.
Here smaller shrubs and plants like seaside golden (Solidago sempervirens) and seaside rosemary (Ceratiola ericoides) can grow. With less wind their seeds will germinate and survive. What wind is still there forces the plants to grow in a round shape resembling green sheep on a white field, instead of white sheep on a green field. My professor referred to them as “beach sheep”. This area of the barrier island is called the secondary dune and includes other species such as false rosemary (Conradina canescens), square flower (Odontonychia corymbosa), and sandhill milkweed (Asclepias humistrata). Though they cannot tolerate the high winds as grasses do, they do have to tolerate climatic extremes and low rainfall.
Small round shrubs and brown grasses within the swales are characteristic of the secondary dune field.
Photo: Rick O’Connor
These secondary dunes vary in elevation and can become taller than the primary dunes. In the low areas between dunes are areas where freshwater water can collect and form ephemeral ponds. These areas are known as swales and create unique habitats much sought after by some wildlife. More bog like plants grow here such as water dock (Rumex orbiculatus) and marsh pink (Rhexia nashii) but also includes the carnivorous plants like the sundew (Drosera rotundifolia). There are many insects who used these ephemeral ponds and many spiders and sundews to take advantage of this.
Behind the larger secondary dunes, the wind is even less, and the dune wind breaks higher. Here trees can germinate, if they can tolerate the climatic conditions, and grow. Though the species that grow out there are some of the same you find on the mainland, here they grow differently. Barrier island trees tend grow out, not up, to avoid direct contact with wind and salt spray. And, when they do reach the wind the portion of tree directly facing the wind tends to be stunted in growth, giving it the appearance that someone has “combed” the tree back towards the bay – something they call wind sculpting. Trees that seem do well in what they call the tertiary dune include sand live oak (Quercus geminata), pine (Pinus sp.), and magnolia (Magnolia grandiflora). Yaupon holly (Ilex vomitoria) and even cactus like the prickly pear (Opuntia humifusa) and the devil’s joint (Opuntia pusilla) can be found growing here.
The top of a pine tree within a tertiary dune.
Photo: Molly O’Connor
Tertiary dunes are some of the largest on the island, with elevations reaching 50 feet or more. These provide excellent wind breaks from the Gulf and allow the formation of salt marshes along the bay side shoreline. Marshes are habitats dominated by grass, but these grasses must be able to tolerate periods emersed in salt water, at least at high tide. Close to the dunes the marsh is dominated by dense stands of black needlerush (Juncus roemerianus). In some locations within the needlerush marsh are areas of bare sand known as salt pans. These are low areas within the marsh where water remains when the tide recedes. These small marsh ponds begin to evaporate in the intense sunlight and the salinity increases to a level where it kills off much of the plant life leaving an area of bare sand. These salt pans are used by some wildlife on the islands. Eventually you will reach the waters edge where smooth cordgrass (Spartina alterniflora) grows. This marsh grass can tolerate water for longer periods than needlerush and supports both island wildlife and estuarine fisheries.
A finger of a salt marsh on Santa Rosa Island. The water here is saline, particularly during high tide. Photo: Rick O’Connor
As you can imagine, the process of establishing the pioneer community of grasses on a new, small sand bar, to an island filled with dunes and vegetation takes time – years, decades, maybe centuries – but eventually it will reach what we call the climax community and provides a variety of habitats to support wildlife.
In part 3 we will begin to look at how animal species colonize the islands as these habitats form.
