Late summer and early fall are a great time to explore our salt marshes. The marsh vegetation is flourishing and marsh critters abound. Areas of marsh ring St. Joseph Bay, forming a narrow fringe along much of the spit, but beginning to widen near Pig Bayou. The bay is home to approximately 762 acres of salt marsh, which coupled with the vast undersea turtle grass meadows, make this one of the most productive bays in the Gulf. The marshes are best viewed toward the south end of the bay at Stump Hole or Salinas Park or climb the observation tower at the St. Joseph Bay Buffer Preserve for a bird’s eye view. To really appreciate expansive marshes, travel eastward to Carrabelle or St. Marks National Wildlife Refuge to witness salt marshes that are miles wide and offer fantastic vistas. Even those marshes pale in comparison to the huge and productive marshes along the Georgia coast.
Since marsh plants cannot root and grow where strong waves occur regularly, salt marshes are indicative of low energy coastlines. On the Florida gulf coast, marshes begin to flourish just north of Tampa Bay. Mangroves, which are tropical plants, dominate southward of Tampa Bay, although we have some cold stunted black mangroves growing and reproducing in St. Joseph Bay.
Whether wading, kayaking or bird-watching along the shoreline of the bay, you probably noticed two main kinds of marsh plants. In the spring and summer, the grasses next to the waters’ edge or along tidal creeks are a bright yellow-green. This isn’t because they get more water. This plant is smooth cordgrass (Spartina alterniflora) and it is found from Texas to Newfoundland. It can withstand a wide range of salinities.
Many people mistake cordgrass for sawgrass, which has serrated leaf margins. Sawgrass prefers a more freshwater situation. Cordgrass doesn’t cut the fingers and tolerates salt water or high soil salt content by excreting salt through special salt glands on the leaves. They tolerate, but do not require salt. Look closely at a Spartina plant and you may see salt crystals covering the surface of the leaves.
The plant that makes up most of the vast Florida marshes is needle rush or black rush (Juncus roemerianus). It typically grows on slightly higher ground, usually behind the cordgrass, and often looks dead and brown. Looking over a Florida salt marsh one mostly sees the dead brown tips of the needle rush. Yet looking closely at the single plant, the visitor sees the leaves are dark green and very much alive. This plant adapts to its salty habitat by transporting salt to the cells on the tips of the leaves which become hard and brown. This plant has a leaf that is round in cross-section and very sharp on the tip. Both of these adaptations serve to reduce water loss by the plant during dry periods in the marsh and protect against grazing plant eaters. The long, round leaf also absorbs wave shock better in storms.
For whatever adaptations these two plants have to survive in their salty world, they are powerhouses at producing food for near-shore marine life. The salt marshes of Florida’s western and upper Gulf coast are giant solar collectors, absorbing the sun’s radiant energy and converting it into food. It has been estimated that marshes produce about ten tons of organic material per acre per year, a rate of productivity as great as that resulting from our best methods of modern agriculture - and all without the addition of one ounce of fertilizer.
While a small part of the marsh grasses is consumed on the stalk by insects and other terrestrial plant eaters, most of it is consumed by marine organisms in the form of organic detritus (finely divided particulate matter of plant or animal origin). This means that the cordgrass leaf becomes useful as food after it falls into the water and begins to decay. The tides carry this bounty out into the bay. Cordgrasses regularly shed their bottom leaves as the plants grow upward and flower. These perennial plants yearly give up their entire above-ground organic production to the dependent plants and animals forming the marine food web. If not eaten directly, submerged seagrasses also enter the coastal food web via the same detritus pathway.
Once considered valueless wastelands and swamps, scientists have researched and demonstrated the true economic value of salt marshes. Fish, birds, and shell fish, virtually the entire coastal ecosystem, relies heavily on salt marshes as a major source of nutrients, food, and for breeding and spawning grounds. Commercial and sport fisheries are dependent on healthy salt marshes. Just to list two examples, juvenile Gray Snappers (Lutjanus griseus) live inshore in tidal marshes, while the adults live in the Gulf around reefs. Striped Mullet (Mugil cephalus) cruise into marshes consuming detritus and algae, and are then consumed by osprey, dolphins, and people. The value of a healthy salt marsh far outweighs the short-term gain as real estate.
In 1990, the marshes around St. Josephs Bay began to show signs of stress and die off. Scientists with the Florida Fish and Wildlife Conservation Commission studied the phenomenon and concluded it was caused by an unknown pathogen. However, that seemed to be linked to a drought that may have disrupted the delicate web of associations in the marsh. Marsh snails without sufficient algae on the leaves to scrape off for food can attack the Spartina plant itself. The marsh snails are in turn kept in check by blue crabs, and anything that reduces their numbers can cause the snail population to increase, which causes damage to the marsh grasses. If we have learned anything about nature, it’s that it is all connected.
Gradually many communities have come to realize the value of intact salt marshes as storm buffers, naturally absorbing storm surge and wave energy. This realization often came after their coastal marshes were dredged and filled for housing and shopping centers, and their seawalls crumbled in hurricanes.
At a meeting recently held at the St. Joseph Bay Buffer Preserve and conducted by staff of the Apalachicola National Estuarine Research Reserve, the components and importance of our marshes were discussed with an audience of researchers, agency personal, public officials, staff from conservation groups, and concerned citizens. For instance, marshes are among the most productive habitats in the world, are important nurseries, and feed both terrestrial and marine life. They provide sediment stabilization, storm and flood protection, wildlife habitat, and filter pollutants from the land before they reach the bay.
One could also add that they provide beauty and recreation. The marshes of St. Joseph Bay are truly treasures deserving of our care and protection.
Tom Baird has been a fisheries biologist, high school and community college teacher (oceanography and microbiology), director of a science and environmental center, teacher of science and principal in Pinellas County as well as an educational consultant. He retired from the Florida Department of Education and he and his wife divide their time between Tallahassee and Cape San Blas.