MARSH ECOSYSTEM

Summary: The Marsh ecosystems of Castilla y León (Spain).

Natural Areas: Lagunas de Villafáfila ; La Nava y Campos de Palencia.

Marshes are transitional areas between land and water, ocurring along the intertidal shore of swamp where salinity (salt content) ranges from near ocean strengh to near fresh water. Salinity, frecuency and extent of flooding of the marsh determine the types of plants and animal found there. The low marsh zone flooding always has water while the high marsh floods only during the winter. Animals and plants that live in these zone of the marsh, depend on how well they can withstand the drier conditions of the upper marsh or the wet conditions that occur in the lower marsh. As a result of this, in the marsh we can to see four vegetation rings: meadows, wetland plant, floating-leaf plant species and submergent plant species. Each ring has its own fauna.
For example, one plant, Common Reed Grass (Phagmites australis) dominates wetland vegetation. Few animal eat this plants, but many animal and plants live on it or the marsh surface protected by its roots and stalks.
Salt marshes rank among the most productive ecosystems on earth. Live Common Reed Grass is not a source of food but dead marsh plants are a source of nourishment for many species. Decaying Common Reed Grass breaks into small pieces called detritus that fuels the marsh and its animals. In spring and summer, marshes are lush green, highly productive and grow in height. In late fall, the green Common Reed Grass begins to turn brown as leaves die and decomposition begins. Water, waves, wind and storms dislodge and break up decaying leaves, and transport them to mud flats and other locations around the marsh. This dead plant matter, or detritus, forms an attachment site for microscopic organisms such as bacteria, fungi and small algae. These organisms colonize the broken bits of plant material and break down portions of the detritus that are not digestible by animals.
For the most part, this decomposition occurs on or in the sediments where bottom-dwelling scavengers such as worms, fishes, shrimps and crabs live. These animals eat the decaying plant material, along with the bacteria, fungi and attached organisms. They then digest the material and excrete the undigested plant remains in feces that can be colonized again by microorganisms. As the microorganisms utilize detritus and reduce it to smaller and smaller pieces, the remaining detritus becomes fertilizer for the next Common Reed Grass crop. In this way, the whole food web cycle is repeated.
Microscopic animals associated with detritus also cover the surface of mud in the marsh. They help stabilize sediments, are food for larger organisms and contribute to an enrichment of the sediments. Large numbers of more sizable invertebrates (animals without backbones) inhabit salt marshes. Rapid changes in salinity, temperature and exposure create stressful conditions and thereby limit how many species occur in this habitat. Fiddler crabs, marsh snails and marsh mussels are typical invertebrate species which live in salt marshes. The popular and highly prized oyster generally borders salt marshes. Fiddler crabs and marsh snails shred dead plant material during feeding, aiding the decomposition process.
Insects are also abundant in the salt marsh. Most of these salt marsh invertebrates consume living plants, or fluids secreted by the plants. Some insects also feed on detritus, though the importance of their role in the food web as grazers and detritus feeders is small compared to their importance to the abundant species of birds who depend on them for food. The undigested grass eaten by insects is deposited as feces on the marsh surface where it becomes part of the detrital food web. Many fish species living near the salt marsh rely on insects for food during part of the year.
Fishes, crabs, and shrimps live in salt marshes where stems, leaves, and roots provide food and shelter from predators. The young of many species, such as the blue crab, white shrimp and spot tail bass utilize the salt marsh as a nursery. Without benefit of an abundance of food and protection given by marsh plants, few younger animals would survive to adulthood.
The regularly flooded salt marshes provide excellent habitat for birds, with many places for feeding, reproducing and roosting. Some bird species alternately eat insects and seeds depending on the season. Other birds feed on fishes, shrimps and fiddler crabs. The commonly heard but seldom seen clapper rail forms roosting areas on the marsh surface within the protective cover of marsh grass. Birds contribute important nutrients to the salt marshes through their feces, which accumulate in large quantities around nesting colonies. In turn, feces fertilize marsh grass, an important function in the marsh food web.
In this unit, our students will work recognizing bird that live in the marsh of Castilla y León. For this, they will learn the external anatomy of the birds with feather type. Morover, they will learn to speak about the habits of these animals, such as reproduction and food.