How Beaufort County’s Salt Marshes Sustain Life with Every Tide

Nursery of the Ocean

Story by Amber Kuehn

The Port Royal area watershed in Beaufort County is unique, boasting more marsh grass in its marine (saltwater) watershed than any other county in the United States. Affectionately called the “Nursery of the Ocean,” it encompasses 200,000 acres of marsh grass, flooded twice daily by the tides — the “Rhythm of the South.” Each tidal cycle in Beaufort County lasts approximately 6 hours, 12 minutes, and 23 seconds, comprising two high and two low tides over a total of 24 hours, 49 minutes, and 32 seconds. This slight extension beyond 24 hours causes a daily delay of 49 minutes and 32 seconds. While the duration of this rhythm remains constant, the volume and speed vary with the moon’s phase and related gravitational pull. Within each interval, water flows faster in the middle of the tidal swing, slower at the beginning and end, and pauses during slack tide before changing direction. This pattern resembles a musical score with a 49-minute, 32-second encore. Although the timing of the tides shifts daily, it is predictable years in advance.

High tide refuge, low tide feast

At high tide, saltwater connects the marsh fields to deeper channels, providing juvenile marine life refuge from predators among the submerged marsh reeds. This creates a game of hide and seek where predators are at a significant disadvantage. Dolphins, for instance, are not typically seen swimming through marsh grass in search of prey at high tide. Instead, they seem to socialize until the low-tide “dinner bell” rings. Dolphins are intelligent and understand that the small fish they consume must follow the receding water, moving away from the safety of the marsh grass with the ebbing tide. These juvenile fish, along with sub-adult blue crabs, shrimp, and others, tend to congregate near the edge of the mudflat, where dolphins patrol a “buffet line.” Locals often use cast nets at low tide to catch bait, small shrimp and minnows. If invited to go crabbing with string and raw chicken, plan for low tide as well. Wading birds stand very still as they hunt in the shallow areas of the waterway at low tide, just outside the nursery. The rhythm of the tide dictates the intensity of predation. High-tide flooding of the marsh enhances juvenile seafood survivability, allowing them to grow large enough to be excluded from some predators’ menus.

A tiny shrimp on someone's fingertip — A tiny shrimp, one of millions in the Nursery of the Ocean, has survived the larval stage — the foundation of the Lowcountry’s intricate food web. As a vital link in the marine food chain, it sustains the next generation of ocean life, ensuring the cycle of survival continues.

A cradle in the current

In the shallow fingers of the Lowcountry waterways, water temperature rises with air temperature. In August surface water temperatures can reach 98 degrees, creating a warm, cozy blanket in the Nursery of the Ocean. Larval organisms are microscopic, numbering in the millions. One blue crab can produce 2 to 8 million larvae, with only one in a million surviving to maturity; the rest become food for other developing organisms in the nursery that are slightly larger. The nursery provides ample food, as various developmental stages offer a range of food sizes, making them all snacks for each other.

bottle nose dolphin strand feeding along the mud flats at low tide — Bottlenose dolphins exhibit a unique hunting behavior known as strand feeding, particularly observed along the mudflats of South Carolina and Georgia. During low tide small groups of dolphins collaborate to herd schools of fish toward the shoreline. They then create a wave that propels both the fish and themselves onto the muddy banks. The dolphins quickly consume the stranded prey before sliding back into the water.

A web of life and renewal

Recognizing that natural processes build upon each other is enlightening. The environment is a web of interdependence. The mudflat is formed by silt collected from the water by marsh grass and held together by its roots. Bacteria within the mudflat process decayed matter to cleanse the waterway. Fiddler crabs living in the mudflat release resulting gases and scour the surface. The marsh is bordered by oysters, each filtering 50 gallons of water daily. The tide flushes the Lowcountry waterways twice daily. Despite limited light penetration, the Lowcountry waterway is considered pristine. Although the water appears dark green due to trillions of larval microorganisms blocking sunlight, it is crystal clear upon close inspection, teeming with life in the Nursery of the Ocean. This story begins with the marsh grass.