Flora and Fauna of Northwest Florida

Biology Department

University of West Florida

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Salt Marshes

The salt marsh at Big Lagoon State Park consists of a tidal creek (bottom of photo) that enters a lagoon surrounded by expanses of black needle rush (Juncus roemarianus) and Salt marsh cordgrass (Spartina alterniflora).

Marshes are part of a larger category of wetlands: partially or periodically submerged lands where the water table is near or above the soil surface. This saturation of the soil causes the sediment to be anaerobic with oxidized to reduced chemical gradients (e.g. sulfate to sulfide) with depth. Wetlands in general have very low relief (little vertical elevation change) and very little or no wave energy. Water that flows into tidal marshes by creeks and bayous floods out over the marsh surface where the water reaches zero velocity and particles can sediment out onto the marsh surface. This acts as a natural filtration system and adds organic and nutrient-rich particulate matter to the marsh system. Tidal saltmarshes are influenced from the sea by both salt water and by the ebb and flow of tides. Tidal marshes are affected by Spring-Neap tidal cycles, with the landward extent of the marsh determined by the highest high tides occurring in the spring part of the cycle.

In addition to anaerobic sediments, salt is a strong force in determining what plants and animals are found in a tidal saltmarsh. Very few plants can deal with both abiotic factors at once, so that salt marshes have very low species diversity. Along the Gulf coast, salt marshes are dominated by Black Needle Rush, Juncus roemarianus, forming extensive monotypic (single species) stands. Spartina alterniflora, or saltmarsh cordgrass, tends to dominate tidal marshes along the East coast of the US, and is found sporadically along the gulf coast, but again in monotypic patches with little mixing with Juncus roemarianus. These plants have different strategies for dealing with salt. Juncus transports the salt to the cells out on the tips of the plant that then become hard and needle-like. Spartina has salt glands that actively secret the salt out onto the leaf surfaces. Despite the low diversity, salt marshes are among the most productive plant communities known. Spartina and Juncus are both emergent plants, meaning they can have their roots in the water, but their leaves are in the air.

Marshes have a tremendous amount of surface area on the stems of the vegetation within the tidal zone. Like most submerged surfaces, these are coated with "aufwuchs", or a fouling community comprised of microalgae, bacteria, protozoa and very small metazoans. The aufwuchs accentuate the filtration effect by trapping particles of the water as is moves between the marsh vegetation. In addition, there are filter feeding organisms (mussels, barnacles, oysters, bryozoans, etc.) that also act to remove particles from the water flooding over the marsh surface.

Because the sediment of the marsh is anaerobic, combined with high production of plant biomass, plant material and organic particles trapped by the marsh do not completely decompose, but become compacted into a peat. Very little of the plant production is directly consumed by herbivores. Most is consumed after the plant dies and it becomes broken up into fine particles known as detritus Many organisms that consume detrital particles do so not so much for the particle itself, but for the microorganisms that "enrich" the particles.

There are both resident and transient fishes and crustaceans in the salt marsh. Many transients come into the marsh as juveniles and use the marsh's surface as a protective refuge from predators as they grow. This "nursery" function is important for many of our commercially important seafood species. Other transients include larger predators that come into the marsh with the tide to feed along the marsh edges on the smaller organisms that venture too far from the protection of the marsh grasses. Many of the resident organisms feed on the aufwuchs, like the periwinkle, olive nerite, grass shrimp, hermit crabs and amphipods. Fiddler crabs like sandy patches in the marsh where they can come out into the air at low tide to feed on microalgae growing on the sand. During high tide, they stay in their burrows to avoid being eaten. Blue and gulf crabs are one of the major predators on the marsh, crushing the shells of many species to eat them, catching small fishes, and eating dead animals.

Trails used by marsh rabbits (Sylvilagus aquaticus) and raccoons (Procyon lotor) through the marsh vegetation are usually obvious. Fecal remains, or "scat", provide good indicators of the diet of these organisms. S. aquaticus is a herbivore, and the round, compact pellets (0.5-1.0 cm) from this organism are dominated by cellulose. Scat from P. lotor reflects its omnivorous diet, containing animal (shells, but mostly unidentifiable stuff) and vegetable remains. Note the seeds of Serona repens that are passed after eating the fruits. This method of seed dispersal is called zoochory. Predation often has profound effects on the distribution of species. P. lotor is also an avid consumer of mollusks, like Blue and Gulf crabs that forage on the marsh at high tide. Note that the distribution of salt marsh mussels (Guekensia demissa) is largely restricted to the root mats between the stems of marsh vegetation (try to get one out with your fingers!), but empty shells and shell fragments are found on the marsh surface. What would you hypothesize to happen to the distribution of G. demissa if we put predator exclusion cages out on the marsh? Also note that the periwinkles Littorina irrorata are mostly restricted to the stems of marsh plants. This species will climb the stems as the tide comes in to stay out of the water and avoid predators. Shell damage on these snails indicates their predation risk.

Dominant Species

Plants

Black Needle Rush

Juncus roemarianus

Salt Marsh Cordgrass

Spartina alterniflora

Saltwort

Salicornia perennis

Salt Meadow Hay

Spartina patens

Saltgrass

Distichylis spicata

Cattail (brackish species)*

Typha angustifolia

Seaside Elder*

Iva imbricata

Wax Myrtle*

Myrica certifera

Yaupon Holly*

Ilex vomitoria

Palmetto*

Serenoa repens

* Found in low salinity marshes or where fresh groundwater reduces soil salinity.

**Found at transition to or border of upland: low root tolerance for saturated sediment.

 

Animals

Molluscs

Periwinkles

Littorina irrorata

Olive nerite

Neritina reclivata

Salt Marsh Mussel

Guekensia demissa

Oyster

Crassostrea virginica

Crown Conch

Melangena

 

Crustaceans

Fiddler crabs (4 spp)

Uca spp

Square Back Crab

Sesarma reticulatum

Amphipods

Gammarus sp.

Green Striped Hermit Crab

Clibanarius vittatus

Gulf Crab

Calinectes similis

Blue Crab

Calinectes sapidus

Grass Shrimp

Palaemonetes spp.

 

Fishes

Long-nosed Killifish

Fundulus similis

Bayou Killifish

Fundulus pulvereus

Diamond Killifish

Adinia xenica

Sheepshead minnow

Cyprinodon variegatus

Sailfin Molly

Poecilia latipinna

Mosquito fish

Gambusia affinis

Tidewater Silverside

Menidia berylina

Clown Goby

 

Stiped Mullet

Mugil cephalus

Spot

Leostomus xanthuris

 

Birds

Rails

Rallus spp

Seaside Sparrow

Ammospiza maritima

Redwing Blackbird

Agelaius phoeniceus

Great Blue Heron

Ardea herodias

Green Heron

Butoroides virescens

Belted Kingfisher

Megaceryle alcyon

 

Mammals

Raccoon

Procyon lotor

Salt Marsh Rabbit

Sylvilagus aquaticus