Salt marshes of St. Joseph Bay

St. Joseph Bay saltmarsh
Special to The Star
Published: Thursday, September 19, 2013 at 09:06 AM.

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.

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