Intertidal and Subtidal Zones

Egrets and Spoonbills search the shallow marsh for food.

NPS

Tides can significantly alter the physical characteristics of beaches along the Florida coast. Tides are defined as periodical changes in sea level throughout the course of a twenty-four hour cycle. At the Matanzas Inlet tides can cause dramatic landscape changes, including the formation of extensive sandbars and the erosion of coastal dunes. Tidal events are really all the result of the moon’s gravitational pull. The moon’s gravity tugs on different parts of our planet as the Earth rotates and the moon orbits about it. The moon’s gravitational pull is so small that we don’t notice it in our everyday lives but, since water is a lot easier to move around than solid material, it greatly affects our oceans. Due to the moon’s presence, water facing it tends to bulge out towards space. This bulge of water creates high tides, which is why when there are full moons the tides are at their peak because the sun, Earth, and moon are in direct alignment. Tides are also high during new moons when the moon lies directly between the sun and Earth.
The movement of the tides create unique ecosystems called intertidal zones. Fort Matanzas doesn’t have rocky shorelines like other intertidal zones (such as in New England), but the park still contains a diverse collection of plants and animals that inhabit and thrive in the different environmental conditions created by varying water levels throughout the tidal cycle. When low tide takes the water away, you can find a surplus of creatures that you wouldn’t be able to see at high tide. A few different types of animals that people may discover at low tide are parchment tube worms, various types of sponges, marsh periwinkle snails, various fish species, oysters, and fiddler crabs.
A specific intertidal zone that is found in the park is the tidal marsh. A tidal marsh (also known as a "tidal wetland") is a marsh found along rivers, coasts, and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea, and in our case, inlet. These marshes provide food, habitat, and nursey areas for many fish and shellfish. In addition to providing habitat, marshes act as a filter, by absorbing excess nutrients from upland runoff that could potentially cause harmful algae blooms in larger waterways. And they also absorb the energy of storms off the oceans and thus help protect inland areas from excessive flooding. That’s an extra added benefit of a healthy marsh when hurricane season rolls around.