In the Salt Marsh

Along the Atlantic Ocean and Gulf of Mexico, from Newfoundland to Florida, you can find a special habitat—the Spartina salt marsh. A transition zone between the land and the sea, this is a challenging place to live for many organisms. I found myself with some spare time while visiting family in South Carolina, so of course I couldn’t resist exploring a nearby salt marsh, one of the most productive ecosystems on Earth. This habitat produces more biomass per meter than almost any other biome. Only tropical rainforests are more productive.

brown grass in salt marsh meadow

A typical salt marsh scene in winter: golden-colored cordgrass.

I reached the marsh near low tide, which exposed soggy ditches and mud flats. The mud was soupy in places, sucking at my boots.

Looking down on boots in soupy, dark brown mud.

Oysters clung together in the lowest reaches of the tidal flats and ditches. The tips of their shells may be fragile, but they are also extremely sharp, as sharp as a surgeon’s scalpel. I don’t know whether the shell’s sharpness is an accident of evolution or an adaptation to protect them from predators like drums, rays, and clumsy humans like me. I do know that I’ll never forget the first time I tried to walk over a few oysters while only wearing flip flops. Trust me, it’s not a pleasant experience.

oyster shell with sunlight passing through translucent upper portion of shell.

The edges of many oyster shells are thin and fragile, but also very sharp.

Walking was easier where vegetation was firmly established. On the U.S. Atlantic coast, most salt marshes are dominated by Spartina grasses. There are several species of Spartina, but the most abundant is salt marsh cordgrass (Spartina alterniflora). Cordgrass thrives in this habitat, despite the harsh conditions—flooded twice-daily by tides, exposed to high salinity, and mired in anoxic (oxygen-free or oxygen-limited) mud.

golden brown grass, trees seen on horizon

Salt marsh cordgrass is the most abundant and ecologically important plant in East Coast salt marshes.

Most flowering plants have a fairly low tolerance for salt, but the cordgrass is watered by the ocean twice a day. Cordgrass meets the salty challenge by sequestering salt in its shoots and excreting the salt through glands in its leaves. The grass deals with the challenge of low oxygen levels in the deep mud by exchanging gases from roots in the upper few centimeters of mud to those underneath. Few plants have these dual abilities, which is the reason cord grass so thoroughly dominates salt marshes. Once you learn to identify salt marsh cordgrass, you can easily and accurately judge the average level of high tide, since cordgrass is usually limited to areas that receive substantial flooding with each high tide.

brown grass of salt marsh, taller rushes on left of photo, trees on horizon

The transition between the low marsh to the high marsh is marked by plants other than salt marsh cordgrass. The high marsh lies above the typical high tide line. Plants like black needlerush (Juncus roemerianus), salt meadow hay (Spartina patens), salt grass (Distichlis sp.), and saltwort (Salicornia sp.) begin to compete with cord grass where tidal flooding is less frequent. Needlerush is the taller plant on the left of the photo.

pinkish, segmented stem of saltwort

Saltwort is a noticeable member of the mid to high marsh community.

Unlike salt marsh cord grass, saltwort tolerates high salt levels through its ability to retain water in its stems, but it cannot withstand the same level of submersion that cordgrass can. Saltwort always captures my attention though, not only because it is a pretty plant, but because it is tasty. Late December is not a choice time for nibbling on saltwort stems. Few were even standing, but the sight of them reminded me of their pleasing salty bite. (I’ve also pickled saltwort using a recipe I found in a Euell Gibbons book. It tasted surprisingly good.)

Before leaving the marsh, I took some time to watch birds out on the lower fringes of the exposed mud. A casual scan through binoculars revealed over a hundred semipalmated plovers. On the edge of the marsh, these birds work to survive the winter before returning north to their breeding grounds from Newfoundland and Labrador west to Alaska.They were also finding a few more invertebrates than I was.

shorebird pulling a worm out of mud with its bill

Worms are yummy for plovers.

My urge to get a little closer to the exposed mudflats brought me to the edge of the cord grass where the mud was very soft. While plovers were pulling invertebrates out of the mud, I was having some difficultly extracting my boots from the mud. Salt marshes are challenging places to live and, if you’re human, difficult places to travel.

looking down on very muddy pants and footware

Salt marsh trekking is dirty business.

4 thoughts on “In the Salt Marsh

  1. Interesting information about the salt marshes. My family was gifted a tract of salt marshes (here in New England) by a King’s grant. Salt marshes were very important to the local farmers as they used the land to graze their milking cows. The prevailing logic of the time was, the cows would eat the grasses becoming extremely thirsty and drink more water, thus, produce more milk. Capitalism at it’s best! I often wondered about this practice as we were warned as kids never to walk on the marshes.

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  2. Another great post! Thanks for pointing out the importance of this ecosystem that many people fail to value.

    I grew up playing around the sloughs and salt marshes in the San Francisco Bay. I too munched on our local species of saltwort. And would slip about in the mud looking for cool critters. I came home more than once completely black with mud. (My poor mother!)

    The difference with west coast salt marshes is that spartina is a dirty word around here. As you pointed out, spartina is highly successful in handling high salt and low oxygen and it is fairly aggressive, so it is a major threat to our native salt marsh species. A lot of time and energy is spent removing it.

    How are the salt marshes holding out on the east coast? In the SF Bay, we have lost 90% of our marshes and we really need them to filter pollutants and moderate tidal flows. Never mind providing food and winter habitat for birds on the Pacific Flyway! Fortunately, a lot of the salt ponds in the south bay have been turned over to local governments by Cargill and are being restored as salt marshes. (We were actually going to go hike in one today, but chose a redwood forest instead…)

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    • Good point. Spartina‘s invasive status in certain areas (it’s also invasive in Europe, China, and New Zealand) illustrates the dangers of introducing (purposefully or accidentally) species outside of their native range.

      There are still millions of acres of salt marsh on the east coast, but development has taken a very heavy toll in many areas. Development of salt marshes is much more extensive in the Northeast compared to the Southeast U.S. Dikes, drainage ditches, and causeways also alter the hydrology of marshes up and down the Atlantic coast. Other looming threats are pollution and sea levels rise. Salt marshes can handle sea level rise on their own, but only if they have the room to migrate. Prehistorically, these marshes migrated landward as sea levels rose, but now people so thoroughly dominate coastlines in many areas that there may not be anywhere for the marshes (and the species living in the ecosystem) to go. The salt marsh is a resilient habitat, it has to be to exist on the edge of the sea, but humans need to give it space remain resilient.

      The lack of opportunities for species to naturally migrate from their historic ranges is one big reason to mitigate climate change. Species still became extinct during past climate regimes when natural forces altered climate, and there wasn’t 7.4 billion people on Earth then. Now species must deal with the perils of a changing climate and human-dominated ecosystems.

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