By Tom Baird
The seasons are turning and while elsewhere people are enjoying the autumn foliage, we can witness impressive seasonal changes in the bay and gulf. Nowhere is this more dramatic than the plants of the upper salt marsh. The upper marsh responds to the seasons and the sea’s touch with varying colors. Seaside goldenrod displays bright bits of color and sea oxeye daisy (Borrichia frutescens) and salt marsh aster (Aster tenuifolius) create bands of color in the zones where they grow. The salt pannes or salt barrens now blaze red with glasswort and these same salt flats may have purslane in bloom. Sea lavender has sent up sprays of delicate purple flowers that make the upper marsh look like it is covered by a lavender mist. The plants of the marsh tell the seasons as clearly as the trees in a forest.
Irregularly flooded by the highest tides and visited by many terrestrial animals, the upper marsh is intimately linked to the regularly flooded lower marsh and eventually to the sea beyond. Plants of the upper marsh contend with extremes of salinity and drying. The majority are halophytes, salt tolerant plants that exhibit modifications and adaptations to their habitat. Succulents and plants with a thick waxy cuticle keep water loss to a minimum. In some marsh plants, salt glands secrete the excess salt taken in from the soli and tides. Salt crystals sparkle from their leaves on dry sunny days. Other plants resolve the salt problem by preventing salt uptake by the roots.
Definite zonation patterns based on their abilities to tolerate salt and drying characterize upper marsh plants. The plant dominating the irregularly flooded high marshes of the Atlantic and Gulf coasts is needle rush or black rush (Juncus roemerianus). Growing on higher ground and generally behind the more productive cord grass, this is the plant that often looks dead and brown. In some sections of the bay, the high marsh is characterized by salt-meadow hay (Spartina patens) and spike grass or salt grass (Distichlis spicata). More birds nest in this zone than anywhere else in the marsh.
Growing mixed with the salt grass in the same zone is the more attractive, but less abundant plant, sea lavender (Limonium carolinianum). Salt glands on this perennial herb help it withstand submersion in seawater. During most of the year the plant is low growing and inconspicuous; then, in a period of less than a week, it flourishes into a showy, delicate, multi-branched spray of tiny lavender blossoms. The high marsh glows with purple flowers, and the migrating butterflies love the nectar.
Parts of the marsh receive such little tidal flooding or run-off from the land that evaporation causes the soil salinity to become excessively high. Only a select few plants are adapted to these harsh salt barrens. One of the few plants able to grow in the salt barrens is glasswort (Salicornia), found worldwide in tropical and temperate regions. The plant is composed largely of succulent, salt-filled, oppositely branching, jointed stems. The genus name, Salicornia, is derived from the Latin sal, meaning “salt” and cornu, meaning “horn,” referring to the plant’s saltiness and horn-shaped stems. Its reduced scaly leaves make the plant appear to the leafless. Glasswort is edible – snap off some and try it – and is used for making pickles or in salads, but is also valuable simply for the variety it adds to the marsh with its fire-red autumn coloration.
Other plants often found on or near salt barrens are saltwort (Batis maritima), and sea purslane (Sesuvium portulacastrum). Saltwort may cover the ground almost exclusively in very saline areas, and can be found in profusion on some of the low islands in St. Joseph Bay. It flowers from spring to late fall and produces a berry. Sea purslane, like glasswort, is edible. The pinks and purples of sea purslane flowers add color to the browns and greens of marshes.
Along the inland fringe of the salt marsh occur species of plants associated with coastlines but growing in areas that are flooded only during the extreme storm surges. This group includes sea myrtle (Baccharis halimifolia), marsh elder (Iva frutescens), seaside goldenrod (Solidago sempervirens) and Christmas berry (Lycium carolinianum), as well as various willows and sumac. It is the cottony flowers of sea myrtle and the small blossoms of marsh elder that attract and feed so many migrating butterflies each fall. Both can be seen on US 98 just east of town and along the edge of the marsh. If you see a bush covered in butterflies during this time of year, it is likely either sea myrtle or marsh elder. Christmas berry brightens the high marsh with bluish flowers and bright red fruit. Blending into upland hammocks is the beautiful and poisonous coral bean (Erythrina herbacea). In the spring, the bright red blossoms of this plant are conspicuous along the marsh edge, as well as, along the roads along St. Joseph Bay. Coastal Indians once made beads from its poisonous red and black seeds, and it is these red seeds that are visible now.
Relatively few animals can endure the extremes of the upper marsh. The clapper rail both feeds and nests in the upper marsh. The diamondback terrapin, the only turtle in the world that lives in brackish and saltwater marshes, hibernates in the marsh muds, but lays its eggs in the sandy areas above the high tide mark. The rough green snake and the salt marsh snake (Nerodia clarkii) live in this zone. Rarely seen, the salt marsh snake is strictly nocturnal. Besides rails, marsh wrens and seaside sparrows are some of the birds that inhabit this zone. Scott’s seaside sparrow (Ammodramus maritimus peninsulae) is the race found locally and is picky in terms of habitat. It is a salt marsh obligate.
Besides resident populations of fiddler crabs, rails, wrens, and terrapins, the marsh vegetation supports many migrants. Raccoons, opossums, deer and mice visit the upper marsh for food.
Considerable research has been conducted on the regularly flooded low marshes, where nutrients and metabolic wastes can be exchanged on each high tide. Only spring tides, storm tides, and wind-driven tides ever cover the upper marshes, where nutrient exchanges are less well understood. Yet, the high marsh plants function as a buffer between polluted water run-off from land and the highly productive lower marsh. Construction set-backs are necessary to protect this critical transition zone, which is not only an important wildlife habitat but a protective buffer for the regularly flooded salt marsh.
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.