If I was asked to select a single plant species that had a major environmental influence on Cape Cod I would choose Spartina alterniflora, also called cordgrass. This species is a perennial plant that grows up to eight feet tall, and is one of the more conspicuous vascular plants in the marsh. Cordgrass is found along the lower part of the salt marsh in the daily tide zone.
When you examine a population of cordgrass growing along the edge of the marsh you might wonder how it can possibly survive in such a hostile environment. After all, any plant surrounded by a salty system will lose water to the environment. However, this species has a unique way of dealing with that problem. In order to survive the exposure to sea water, cordgrass removes salt through its leaves. Rub your fingers along one of its blades and you can feel the tiny salt crystals.
The plant has also evolved another unique adaptation to the salt marsh. The substrate is an anaerobic environment which would normally be fatal to any plant. However, cordgrass has specialized cells in the leaves for moving oxygen to the roots, thus providing their own source of needed oxygen.
Another interesting ecological feature of this plant is that it creates a protective habitat for rockweed and ribbed mussels. The rockweed acts as a canopy over the mussels, and the cordgrass stabilizes the land and banks for the attachment of the seaweed. This form of zonation is particularly visible at low tide.
When cordgrass dies and decomposes, it forms large mats of decaying vegetation called detritus. Some of these mats are transported into the bay where they are consumed by numerous microorganisms and tiny animals. This detritus represents an important organic food source. It ultimately supports invertebrates and fish, either through direct grazing or indirectly as an energy source through the food web.
A portion of the mat may remain at the high tide mark or wash into tiny pools, or pannes, in the marsh. There it provides additional nutrients and shelter for small living things, as well as enriching the sediments as it decomposes.
Sometimes large chunks of peat break away from the banks of a marsh. These small islands are called hummocks and may have a population of cordgrass already attached. If positioned correctly in one of the creeks, they can get established and the grass continues to trap additional sediments. This is one way in which the marsh can grow and expand.
Ironically, this important species in Massachusetts is considered a pest in other parts of the country such as Washington and California. It has become invasive in parts of those states and has out-competed several native species. But here it is at the top of my list for significant plants along the coastline.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.