The oceans cover 70 percent of the earth’s surface. Early on, they were not nearly as salty as they are now. The rains, great rivers, and inland seas that created them washed in billions and billions of tons of soils and the salts contained in them. Meanwhile the seas were evaporating from the surface, leaving the salts behind; thus they became even saltier.

    It took awhile for animal life to work out subsistence in a salty medium, but having gotten the hang of it more than 300 million years ago, it flourished, in particular the invertebrates and the fish.

    Seaweeds — there are thousands of them now — also evolved to handle life in the briny. They further developed pseudo-roots, called holdfasts, to tie them to the sea bottom and rocks at the shore so the tides and waves didn’t sweep them away.

    Flowering plants, the ones that produce seeds, having gotten their start on land and in freshwater wetlands and ponds, had the most difficult time of all dealing with salt regimes. They have yet to conquer the seas; there are only a handful of them that have done well over the millennia.

    Those that have, such as eelgrass, Zostera marina, had the sea shallows all to themselves, save for the seaweeds, and so were able to spread throughout the world’s oceans.

    While the seagoing aquatic flowering plants were making a go of it, another group of salt-tolerant plants was developing along the world’s coasts. They had an even more difficult job working out a life strategy: They not only to contend with saltwater from each day’s tides, they had to handle storms, droughts, and other episodic events — acts of God — that made it difficult for land plants to contend.

    Nevertheless, a few hardy plant families managed to overcome all the hurdles and today they make up the world’s salt marshes. No continent, save Antarctica, is without them. The Americas and their Atlantic Coast are no exception: They have the richest, most productive salt marshes in the world, stretching from Labrador and Nova Scotia in Canada all the way to Tierra Del Fuego at the southern tip of Argentina.

    They differ here and there, but they all have many of the same species, or cousins of the same species. They all differ in their tolerance for salt and tidal inundation. Only a few can handle the semi-diurnal tides that we have along our coast.

    Chief among them is Spartina alterniflora, saltwater cordgrass. It doesn’t mind being awash in brine two times a day; in fact, it thrives under such conditions. It’s a perennial that gets going in mid-May, grows to a meter in height or more, flowers at the end of July, and seeds in late August and early September.

    While the seeds are resistant to marine conditions, they are atavistic, remembering their past, as it were, they only germinate in freshwater. Consequently, almost all cordgrass reproduction is by underground extensions called rhizomes.

    You almost never find a healthy salt marsh along our coast without healthy saltwater cordgrass. It ties down the marsh, trapping sediments from the tide, as do the ribbed mussels that live in the peaty soil that they help build. Once the forepart of the marsh is stabilized, all sorts of salt-tolerant species come in behind, the most dominant of which is another spartina grass, salt marsh hay, named such by the colonists because it was gathered and used as a winter fodder for livestock.

    Salt marsh hay and the other plants that grow with it, spike grass, sea lavender, salt marsh aster, salt marsh gerardia, and black grass, to name some of the more common forbs and grasses that grow with it, can handle salt water, but only a few times a month, during the new moon and full moon tides. Too much salt will do them in.

    Two shrubs, marsh elder and groundsel bush, or sea myrtle, also occupy salt marshes, the former sometimes called high tide bush because it grows just beyond the upper edge of the mean high tide, the latter safely ensconced on the landward edge of the salt-marsh-hay zone.

    Between the intertidal marsh and the high marsh is another group of plants, the salicornias or pickleweeds, seablites and arrow-grasses, that are in between the other two zonal communities in their tolerance for salt.

    Here is where the fiddler crabs most like to dig their holes and establish their colonies. Muskrats dig burrows in the intertidal peat, mice live in the high marsh, lots of mammals, including raccoons and deer, forage throughout both zones. With all of the critters that live in, and use, the marsh, it is well fertilized.

    Because so few plants can handle the salty conditions that drive the tidal marsh, and maintain it in a climax condition, the plants that live there are secure from invasion by exotic species, say, weeds like mugwort, Japanese knot–weed, bittersweet, and garlic mustard, with one very big exception.   

    Ditch reed, Phragmites australis, the genotype imported from Eurasia, is the only serious invasive our native salt marsh plants have to fear, and fear they must. This nasty but attractive 10-foot-high grass is the bamboo of the salt marsh, equally sinister in design and intent.

    It doesn’t like salt all that much, but has developed a different strategy for dealing with it. It sends out rhizomes from an upland base that carry fresh water and nutrients to the new shoots arising in the marsh. In this manner it is able to establish a dense system of these feeding tubes, all of which produce new shoots, the new plants eventually becoming a dense interlacing monoclonal stand, forcing out everything else.

    Once phragmites comes in, there go the fiddler crabs, ribbed mussels, and other birds and mammals that frequent the normal healthy diverse salt marsh. Phragmites occurs throughout the world and in New York State it is an enemy of not only the salt marshes but also all freshwater wetlands, to wit, the Hackensack Meadows in New Jersey, where Giants Stadium is located.

    At times, a native salt marsh species in one region will become an invasive in another. Not only do salt marshes in California have to contend with phragmites, they also have been invaded by our saltwater cordgrass, which is displacing the native one, Spartina foliosa, which is similar in appearance and habits. This is particularly so in the San Francisco Bay region, which support’s the state’s biggest collection of salt marshes.

    Other than takeover by phragmites, the other major problem that our salt marshes face is drowning. Sea level is rising so quickly that the marsh can’t accumulate sediments quickly enough to keep up with it, as it has in the past.

    In Accabonac Harbor, for example, in places the marsh peat is 17 feet thick — that’s how much sediments have been building up in the less than 12,000 years or so the salt marsh has been building there. This computes to less than a millimeter a year or so, but sea level is rising faster than that now.

    The marshes will either have to retreat farther inland to where the topography is gentle, or be artificially supplied with sediments dug from harbor bottoms and sprayed on top of it, the way stucco is sprayed on the side of a building.

    Attacked from both sides by rising sea level and Eurasian phragmites, salt marshes have never been in such peril. Even the Terminator will have a difficult time saving them — at least he will have in California, where he presides. We don’t have a terminator on this coast, do we?