As the season changes, spring seems to come while the tide is out and winter creeps back with the cold water of high tide.
8
The marsh mud is warmed at low tide, for there is no tall grass to shade the surface. When the tide turns, heat stored in the thin warmed layer of mud passes into the cold water that creeps up. The water is slightly warmed but then goes back and mixes with the great reservoir of cold water at the edge of the sea. Many sunny days must pass before the heat penetrated very far into the water.
Most intermediate-sized animals are safely buried some inches under the mud or the water and will not come out into the world until the warmth of spring penetrating slowly deeper and deeper into the ground, finally arouses them to the surface.
But most of the activity of the marsh takes place at the surface of the mud. Animals, plants, and bacteria concentrate at the mud surface and are subject to the full force of the sudden changes of temperature, salinity and water level that occur there.
Plants
Plants, one-celled diatoms and flagellates, grow in full sunlight on the solid surface where fertilizing nutrients are concentrated.
9
The ideal spot to find food, light, and the necessary nutrient elements for plant growth is at the surface of the mud where any food settling from the water must come to rest. But it is also the place most subject to change in temperature as the sunlight comes and goes and the tides ebb and flow.
In spite of cold nights, gray, cold and rainy days, the mud does thaw and gradually warms up. Plants begin to grow again. The mud on the creek banks turns a rich brown in the morning sun as the diatoms and dinoflagellates become abundant on the warm mud. Spartina seeds, that escaped the birds and insects and fell into the mud the preceding fall, sprout. Later, the shoots in the high marsh manage to push their way through the cover of last year’s grass. The marsh begins to green up.
Animals
The animals are also warmed and begin to be active again. Their food needs increase. The fiddler crabs suddenly appear above ground when the temperature reaches about 60°F in their holes.
Birds
The sun continues to warm the edge of the land and the ribbon of green marshes is seen again along the coast. Male marsh wrens move in to the fast growing Spartina along the creek banks and begin staking out their territorial claims building nests one after another. The marsh rails begin their nests hidden among the Spartina, but the nests are too heavy to be supported by the grass and rest on the ground.
10
The birds collect their food and for their nestlings on the marsh. Insects from the Spartina and snails and crustaceans from the mud are taken.
The tempo of life speeds up in the spring in the marsh as it does on land, except that it is complicated by the tides, by the slowness with which the water warms ups in comparison with air, and by the changes in temperature and salinity as a result of spring rains. As the summer advances, the activity of the marsh reaches its maximum. Growth of new plants and decay of old vegetation proceed at their greatest rates.