Habitat Reconstruction: Restoring Salt Marshes

Rezek RJ, Lebreton B, Sterba-Boatwright B, Beseres Pollack J (2017) Ecological structure and function in a restored versus natural salt marsh. PLoS ONE 12(12): e0189871. https://doi. org/10.1371/journal.pone.0189871

 

Restoration.

As society stretches itself further and further we are witnessing the strangling of our coastline. Urbanization and agricultural have decimated the productive and pristine estuaries encircling most of the world’s coasts. These impacts are not foreign to the United States. Since the late 1700s nearly 50% of all coastal marsh habitat along the Gulf of Mexico has been lost. In Nueces Bay, an estuary located in southern Texas, nearly 150 acres of salt marsh habitat were lost during the creation of US Highway 181 in the 1940s. Several decades later, in 2011, a restoration project was initiated to replant much of the lost native salt marsh grasses.

Replanting salt marsh plants and establishing new marshes brings a lot of good to the ecosystem. It can assist in many natural processes as well as establish nurseries for many commercially important fish and migratory birds as well as reduces the amount of pollutants entering the ocean. But how well are these restored marshlands mimicking a natural unrestored marsh?

A study by Rezek and fellow researchers hoped to answer this question. Through the aid of chemical isotope analysis, they hoped to understand how these added plants may affect the animals living in the surrounding estuary and depend on the habitats these plants provide.

The research base, Texas A&M Corpus Christi campus. Source: Wikicommons

What Are Isotopes?

The world is made up of chemicals. These chemicals are made up of atoms such as carbon and nitrogen. But not all atoms are equal. For example, 12C has six protons and six neutrons while 13C has six protons and seven neutrons, these are different carbon isotopes. It just so happens that salt marsh plants have specific isotopic signatures, therefore anything that consumes or uses parts of the plant may pick up those isotopic signatures. This means that scientists can collect samples from both marsh plants and animals in the restored and unrestored areas of the marrsh and see how the plants may influence the diets of the animals. From isotopic analysis scientists can determine the impact replanting salt marsh grasses has on the food chain.

A great egret standing in Nueces Bay, Texas. Source: Wikicommons

What They Found.

Before diving into the isotopes, the researchers first examined the plants and their surrounding environment. Four years after the restoration, they found the restored marsh had a similar size of plants that matched that of the neighboring natural marsh. Each marsh sustained similar ecologically important animals. So on paper it looks like the restoration process was a huge success! Not so fast, what about the isotopes? By examining the isotopic signatures found within dozens of invertebrate species from both marshes, the researchers were able to determine how important the plants were to the critters. It turns out that i the natural marsh, the plants make up a significant portion of the species diets’ but in the restored marsh the animals still rely on the nutrients in the water rather than the plants.

In conclusion, both marshes looked identical from afar, but upon further investigation the restored marsh plays a less significant role in the food chain than the natural marsh. It has been estimated that plant characteristics in a restoration project will recover within 5 to 15 years while its overall influence on the ecosystem may not be seen for several decades. The major takeaway from this research is that restoration projects don’t simply “fix” ecosytems overnight, it takes a long time for nature to recover to what it once was.

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Aidan Barry

I am in the process of earning my Master's in Natural Resources from the University of Connecticut. I am fascinated by potential shifts in biological processes due to climate change. My research is focused on how sea level rise and restoration practices may alter biogeochemical processes of salt marsh vegetation as well as the microbial community. When I'm not in the lab or covered in marsh muck, there's a god chance I'm down at the beach either surfing or fishing.

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