This Earth Cache will lead you through Robinson Preserve along the Spoonbill Trail to one of the best views of the preserve's salt marsh habitat. Learn about the geology of this special place and discover why it's a often described as a sort of "Floridian desert."  

Welcome to the Salt Marsh!

Robinson Preserve Salt Marsh. Photo by George Donohue - Taken in 2013 when this Cache was first listed

To log this earth cache, please complete the following activities. And remember, you DO need to send in the answers! Please email team_nell with your answers

1. (Updated 2024 as much of the marsh is transitioning to mangrove forest): When this cache was originally created in 2013, much of Robinson Preserve was a salt marsh. Over time, the land has changed tremendously. Look at the gallery and the past logs of previous years and compare them to what you are seeing now. How has the land changed over time? How has the land transformed over time?
Previous Question from 2013-2024: Observe the plant life growing immediately beyond the object at GZ. Look around it and note how much of the ground is NOT covered by plants. Estimate the percent coverage of plants, and the percent that is just open saltern or salt pan. Hypothesize why these areas do not have any plant growth.

2. Take a photo at GZ facing north. Try to get the ground as well as the water; these photos will create a journal of the area's growth over time. (optional) If you do not do a photo, count the number of plant species you can see. How many are present? Hint: look at color/size/type of leaf to try to discern different types. It is not necessary to be able to identify them.

3. (Updated 2024 as much of the marsh is transitioning to mangrove forest): Walk around the area and see if you can find any places to look out and see what remains of the marsh. See if you can spot the tall marsh grass that grows along the water's edge. This is Spartina alternaflora, smooth cord grass. Carefully observe the water line. At the time of your visit, is the grass underwater or above it? Record your time and observation.

4. Hypothesize the role these plants play in maintaining the structure and form of the habitat. Describe in your own words how these plants help the system and the soil. 

5. Note any wildlife that you find - bonus points if you post a photo! (optional)

This is my FAVORITE Florida feature. Why? Because it looks, well, rather unimpressive and uninspiring...but once you really start to examine it you'll find that this habitat is filled with all sorts of amazing wonders. Let's look around to see what we can find!

Salt marshes are the place where the land and water meet. These habitats are a type of wetlannd that has saline soil and are usually located on the border of saltwater bodies or esturaine (a mix of fresh and salt water) waters. These habitats are unique in that they are heavily influenced by the tide; the areas are generally covered by water at least part of the day. Many of the plants and animals that live here, then, have adapted to the influx of the tide and the sudden flooding as the water rushes in. Native plants have grown spreading, runner-like roots to better cling to the soil, allowing them to survive the tidal action. The wildlife too have learned to live with a changing system, moving into the tall marsh grass to hide from predators when the water is high and covering the base of the plants, and then retreating as the tide exits.   

Fiddler crabs make their home in the mudflats and salterns scattered amonst the high marshes. Photo by Dotty Motta
 

The salt marsh can be divided into several different areas or zones.  A section of the marsh is subtidal and under water, then the marsh opens into the expanse of the mudflats, followed by a grassy low marsh and a high marsh with a much greater plant diversity. Here at Robinson Preserve, there are patches of saltern (mudflats or salt pans) in among the high marsh. At low tide, when the water is far away from the plant life, you may see mudflats closest to the water, then the low marsh, then salterns, then the high marsh. The low marsh floods frequently, often twice a day, while the high marsh may only have water during extreme high tide events. Because of this difference in tidal events, a strigkingly different plant community can be found in each location. Even so, with the prospect of regular flooding very few plants can grow in these areas. Those that do are halophytes, a plant that grows in waters of high salinity, and as mentioned above possess specific adaptations to allow them to survive. At Robinson Preserve the tall grass you see growing closest to the water's edge, for instance, has special salt glands that help it secret the salt that builds up as it soaks up the water throughout the day. Look closer inland to the saltern and  you will see a vine-like plant spreading across the flats. This is sea purslane, another halophyte, and its survival strategy is to absorb and store the salt in its fleshy leaves. The diversity of plants is very low in these areas because so few plants can survive in this harsh environment. 

Spartina, smooth cord grass, in the low marsh at Robinson Preserve. Photo by Jan Reises

 

The soil of the salt marsh is predominantly sandy or clayey and very saline; containing a great deal of salt. It may be surprising, but the soil is actually rich in decaying organic matter and nutrients. In the low marsh area the soil is made up of mud and peate. The peate is made of decomposing plant matter and can be several feet thick. At Robinson Preserve, only the smooth cord grass and mangrove trees can flourish here in the low marsh, but the grass is still a major producer in the system. The grass is a food source for resident snails and, as it dies and is broken down by bacteria, for tiny fiddler crabs. Its presence softens the blow of the waves, absorbing energy and preventing erosion too.

Elevation in the Salt Marsh. Image courtesy University of Florida IFAS

 

Elevation changes in the salt marsh are just a mere matter of inches, but they result in a transformation of the landscape. As the elevation increases across the marsh, moving from the water up the shore, the pH of the soil and the amount of organic matter decrease allowing for a greater diversity of plant life. Even so, there is still a great deal of salt in the soil here - while the salt water may evaporate, the salt is left behind and builds up within the soil. These plants, too, are halophytes and can handle the salty soil, but not the constant flooding of the low marsh. 

Yellow crowned night heron feasts in the salt marsh. Photo by Dotty Motta 

The salt marshes found along Florida's coast are in decline. Here in the Tampa Bay region, the area has lost over 70% of its salt marsh habitat due to development. Robinson Preserve is a special place as this habitat has been preserved for the wildlife, and the human visitors, to enjoy. This transitional zone, as a wetland, absorbs and traps pollutants before they reach the water. In this case, Robinson Preserve's salt marshes help protect the waters of Sarasota Bay. The plants prevent erosion, serve as a "nursery" for small fish and invertebrates who live within them during the various tidal cycles, and become an eatery for the larger predatory wildlife who hunt wthin that same "nursery." Widely considered one of the most productive plant communities in the world, this habitat can produce up to 80 metric tons of plant matter a year! And if you like to fish, hidden within the tall grasses are the young forms of over 70% of our state's most popular commercial fishing and shellfish species. These important coastal communities, while seemingly only harboring a few species, actually present a huge diversity for creatures all across the food web and at all stages of the life cycle.