The Critters that Call the Salt Marsh Home
Photo Credit: Danielle Meeker
Driving down the causeway to Seven Mile Beach, you can’t help but notice the expanse of salt marsh outside your window. As summer approaches, those watching get the privilege of seeing the marsh turn from a dull brown backdrop to a lush landscape teeming with life. Maybe they roll down their windows and breathe in the salty air mixed with a little low-tide mud smell. It is easy to drive by with eyes on sandy beaches and an endless ocean horizon, but there is so much to love and appreciate in the salt marsh.
The salt marsh is a wetland ecosystem that develops between upland habitat such as forests and low-energy intertidal zones. The dominant factor that influences this habitat is tides. Every day the salt marsh experiences two high tides and two low tides. High tides flood the area and all the surrounding plants and animals with salty water. About six hours after a high tide, the water has receded, leaving all of those same organisms exposed to the elements. Plants and animals that live in this habitat must be able to withstand constant changes to their environment.
One type of animal uses the power of tides to its advantage when feeding. Bivalves, a type of mollusk that has two shells, do what is called filter feeding. By ever so slightly cracking open their shells, bivalves use their siphon, which acts as a straw, to suck in water and filter out any plankton or organic material that is in it. At each high tide, bivalves are flooded with food and nutrients that sustain them.
There are many types of bivalves in our salt marsh, but some of the most commonly seen are ribbed mussels, eastern oysters, and hard clams. All three make their home in a salt marsh but prefer different locations within it.
Ribbed mussels (Geukensia demissa) are found firmly attached to the base of salt marsh grass, or Spartina alterniflora. They use strong byssal threads to anchor themselves in place, where they will live out the rest of their lives.
Oppositely, hard clams (Mercenaria mercenaria) prefer to call mud flats home. In the soft mud, hard clams are able to use their foot to orient themselves and move when submerged in water. But at low tide, they bury themselves to avoid predators and exposure to the elements.
Lastly, eastern oysters (Crassostrea virginica) require a hard surface to grow on. As juveniles, oysters float as plankton until they hopefully land on a hard substrate and begin to grow into their adult form. They can often be seen growing on other bivalves such as other oysters or mussels and off of rocks and pilings.
Despite their differences, all three of these bivalves help to maintain this ecosystem by filtering the water and creating habitat for numerous other organisms.
When looking out across the green expanse of the salt marsh, it can be surprising to learn that salt marshes are some of the most productive and diverse habitats on earth. In fact, the productivity of salt marshes is often compared to that of rain forests. Darting in and out of the grass shoots and moving just below the surface are an uncountable number of fish, crabs and mollusks that start their lives in the safety of the salt marsh. In the obscure network of tidal creeks and bivalve beds, animals use the complexity of the habitat to hide from predators that are unable to navigate and traverse these spaces.
One such fish is the Atlantic needlefish (Strongylura marina). Shooting just below the surface of the water is this thin, silvery fish with a long, pointed jaw. As adults, needlefish can grow up to 2 feet in length, but in the salt marsh juveniles are usually only a few inches long. Juvenile needlefish are a quick snack for most predators, so they hide at the surface of shallow water where their thin silver body looks like a glimmer of sunshine on the water.
Swimming below the needlefish is another juvenile dodging predators. Black sea bass (Centropristis striata) are a very popular fish for recreational anglers, but before they end up on a fisherman’s line, they start their life in a salt marsh. Black sea bass lay eggs in estuarine habitat, where freshwater mixes with salty ocean water. Once hatched, the larval sea bass float until they begin to develop into their juvenile states. Juveniles exist in four color stages, becoming more brilliant and aggressive as they grow. After one to three years, the sea bass are ready to migrate offshore into deeper waters.
Even deeper, tucked inside an oyster reef is an unassuming mottled fish called an oyster toadfish (Opsanus tau). These fish are bottom dwellers that hide among oyster reefs, wrecks and other debris to escape predators. They also use their incredible ability to camouflage in order to catch prey for themselves. These pesky fish are often considered a nuisance fish to fishermen, many of whom nickname them oyster crackers for their strong bite.
Hiding nearby, tucked into a sea grass bed, are lined seahorses (Hippocampus erectus). Lined seahorses are the only species of seahorse we have in our area. They live their entire lives clinging to sea grasses, crab pots, ropes and pilings. They camouflage so well into their environment that they have next to no predators. Seahorses mate for life and are often found in pairs. As poor swimmers, seahorses hold onto substrates and wait for food, such as small crustaceans, to come to them. These animals rely heavily on their habitat to provide food and safety.
For some of these organisms, the salt marsh is their forever home. For others it’s a nursery, where they are safe to grow before it is time to venture into deeper waters. As a whole, the salt marsh is home to an incredible diversity of plants and animals. It is estimated that about 68% of commercial seafood utilizes wetland habitat and that at least 75% began its life in a salt marsh. Not only that, but more than 180 million Americans visit estuaries and coastal waters for recreation and tourism.
Hopefully, the next time you take a drive past the marsh, you see something more than waving green grass. Knowing and understanding the value of this habitat to the organisms that call it home and the humans lucky enough to visit it is a great way to begin to appreciate the salt marsh. To do just that, visit us at The Wetlands Institute or explore our Virtual Wetlands Experience online at wetlandsinstitute.org. Discover more about these animals through our virtual Creature Features or in the Watch Tank!
