Life of the Salt Marsh

Hilton Head Island, like most of the Lowcountry, is defined by one of the most remarkable natural systems on Earth, the salt marsh. The marsh has been described as a biological factory without equal; more fertile than an Iowa corn field, and responsible for producing an incredible amount of biomass. 75% of all the commercially caught seafood will spend some point of its life in a salt marsh.

Twice daily, the marsh is inundated with a fresh supply of nutrients, through a massive exchange of water, courtesy of our tides. Plants and microorganisms break down these nutrients and use them with amazing quickness. This tidal cycle nourishes the vast swaths of salt tolerant Spartina grass, by far the most important plant of the marsh. The cane-like stalks of spartina are the backbone of the marsh’s production, creating nourishment and protecting the young of blue crabs, shrimp, flounder, menhaden, mullet, oysters and dozens of ecological and culinary importance.

The salt marsh is a harsh, stressful place for its residents. The plants and animals that live here must be super-hardy, able to tolerate drastic changes every few hours as tides advance and retreat. If one thing defines this taxing world and dictates who survives here, it is salt, mostly common sodium chloride. Salt marsh organism, both plant and animals, must adapt to varying degrees of salinity. In fact, many marine marsh creatures need particular salinity levels at various stages of their lives, and salinity may dictate when and where they reproduce.

black needlerush figures predominately in the high marsh zone.

The High Marsh Zone

The marsh is broken up in zones, the high, mid and low marsh. The high marsh zone contains a mixture of plants. Sea lavender, saltgrass, saltwort, and small stalks of spartina appear, but the dominant plant here in this zone is black needlerush. Named for their extremely sharp tips, which can easily puncture skin, needlerush grows in soils ranging from almost pure sand to fine silt loam and clay mixtures. It also has a high tolerance for anaerobic conditions and helps dilute organic waste that runs into the marsh from the land’s edge, breaking it down before entering the tidal creeks.

In the high marsh, the spartina grass only grows to around a foot high due to the salt content. This is the saltiest part of the marsh and is flooded with seawater for a short period of time each day. As the water evaporates, the salt concentration of the soil increases. Evaporation causes the surface water to draw up more water from below the surface which continues to evaporate and leaves the soil with a high salt content. It’s not uncommon to find areas of the high marsh zone that the concentrations is so great- over 3 times saltier than seawater- that nothing is able to grow. While void of vegetation, these salt pans are wonderful areas for spotting bird and animal tracks.

The Mid Marsh Zone

Entering the mid marsh, the vegetation is solely spartina grass. Ribbed mussels protrude from the soft mud. Periwinkle snails, the “farmers” of the salt marsh, cling to the spartina stems. As the tide rises, the snails will ascend the stems on their single foot to evade the claws of ravenous blue crabs brought in by the tide.

The spartina’s robust root system here, wide-reaching roots and root-like rhizomes create a relatively firm but squishy walking surface along the pluff mud. In this area, small organisms are actively working. Bacteria, algae, fungi, protozoa, nematodes, copepods, and other microscopic life live in the billions per square inch in and on the mud.

Periwinkle snail "farming" on a stem of spartina grass

Ribbed mussels in the low marsh zone

The Low Marsh Zone

Here in the low marsh zone, along the creek bank, is an ideal environment for spartina. The marsh grass is at its most luxuriant here, growing as tall as nine feet and producing more than 17 tonnes of biomass per acres annually. The tides efficiently bring in loads of nutrients and sediments to the upper creek bank and washes away salt, dead matter and other wastes. Changes in temperature and water salinity are minimal here. The mud is better aerated here, with the help of fiddler crabs, constantly burrowing into the mud for refuge and food. It’s estimated that a million fiddler crabs or more inhibit just one acre of healthy salt marsh.

This zone is teeming with life; a variety of microscopic organisms such as fungi, bacteria, and algae cover the mud. These provide sustenance to the meiofauna, a collective term for the ultra-tiny creatures such as nematodes, protozoans, copepods, amphipods, and annelids that live on or just below the mud’s surface. The macrofauna, which are more visible, forage for the meiofauna, as well as for algae and bits of dead spartina grass. Mud fiddlers, marsh crabs, snails and polychaeta worms are just some of the macrofauna that can be found in the area. Oyster beds also line the creek banks, while ribbed mussels are particularly abundant in the lower marsh.

The Need to Protect

The significance of the marsh cannot be overstated. Not only does it serve as a crucial habitat for several species, but its loss would have far-reaching consequences. Without its role as a nursey for shrimp and crab larvae, commercial industries would suffer. Losing oyster habitats would mean the loss of a natural filter for regulating the health of adjoining waters, as well as the loss of a valuable barrier against storm erosion. The loss of spartina grass would have a ripple effect, leading to habitat loss for nesting birds, foraging mammals, and juvenile marine life. Additionally, the detritus from the spartina grass plays a critical role in the ecosystem of creeks, sounds, and oceans. Without it, the balance of marine life could be severely disrupted.

To learn more about the salt marsh, check out the Coastal Discovery Museum! They have an extensive array of information regarding this amazing habitat as well as in depth lectures. Or come out on a tour with us! We’d love to show you how important this is to the future success of Hilton Head and our surrounding area

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Life of the Salt Marsh

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