What is a salt marsh?

Based on research by Hayoon Chung, MIT ’16

Salt marshes are the transitional coastal ecosystems between the land and ocean, where saltwater and freshwater mix. Salt marshes are known for their rich diversity and productivity. Of all the ecosystems in the world, salt marshes are the most productive.

When people think of biodiversity, life, and energy, they often think of rain forests. However, the often neglected salt marshes rival tropical rainforests when it comes to life and productivity.

Salt marshes are not physiologically identical throughout its habitat. Because it is the boundary between land and water, there are three distinct areas, ‘zones’,  that differ in conditions and characteristics. These zones are often defined by the various salt marsh plant species that thrive in specific elevation ranges. (Pennings and Bertness 2001)

Submerged zone: This is the lowest portion of the salt marsh in elevation; it remains under water. Because of such characteristics, this area is mostly populated by animals such as fish and crab.

Intertidal zone: This is the section of the salt marsh where the tide most frequently washes over.  It fills and drains during high and low tide cycles. Plants that live in this area are generally stronger species because of the physical stress that they need to withstand. Such stresses include the incoming waves and tides, as well as the salinity of the water. This zone is less productive than  higher zones are because of the physical stress. Physical stress is what sets the bottom bounds and limits of this zone.

Supratidal zone: This is the area of the salt marsh that is highest in elevation where water less frequently washes over. Plants that live in this area are generally weaker species because of the more favorable and ideal conditions of the zone. There is no intense physical stress from waves or high salinity of water. However, because it is a more ideal habitat, there is a lot of competition amongst the plants. Such inter-species competition is what sets the upper zone boundaries in this area. This area has the higher productivity because of its ideal conditions for the plants to live in.