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What is the Littoral Zone and Why is it Important?

July 5, 2023

While it may sound like a state of mind devoid of allegory or a place where what you see is what you get, the littoral zone is really a much murkier territory. Littoral comes from the latin littoralis "of or belonging to the seashore," and it’s the transitional area between dry land and open water—an intertidal zone that is sometimes above and sometimes below the water level. Littoral ecosystems vary widely from place to place, as they are related to local conditions including climate and the hydrological and geological features of shorelines and nearshore bottoms. Species that inhabit or regularly visit this intertidal territory are vital for ecosystem health and perform a number of ecological services such as facilitating energy and nutrient exchange between land and water, providing nurseries for aquatic organisms, stabilizing shorelines, contributing to water filtration, and supporting overall biodiversity. That’s why conserving and managing shorelines is essential! Get to know and appreciate the locals with our line-up of some of the key characters found in the Northeastern Atlantic littoral zone.

1. Red Knot

Red Knots are plump sandpipers that inhabit shorelines, foraging for aquatic invertebrates by probing the sand with their long bills. They are marathon long-distance migrants, flying each spring from the southern end of South American to Arctic nesting grounds. During this arduous journey, they rest and re-fuel in vast hordes at traditional stopover points such as the Delaware Bay, feeding on the eggs of horseshoe crabs. Nearly 90% of the entire population of the Red Knot subspecies rufa can be present on the bay in a single day. The overharvesting of horseshoe crabs is partly responsible for a sharp decline in Red Knot populations.

2. Horseshoe Crab

Horseshoe crabs are one of the world’s oldest species–estimated to be at least 300 million years old–and are more closely related to scorpions and spiders than they are to crabs. Despite their rugged visage, with hard shell and long tail spike, they are harmless to humans. During their breeding season, they spawn at high tide along the shore, burrowing into sand and mud to lay their eggs, thousands at a time. Many species rely on these eggs for food, notably the Red Knot, which has for millennia depended on them to fuel the last leg of their long migration to the Arctic. Additionally, their unique copper-based blue blood has biomedical applications. This has led to the overharvesting of the crabs, and in turn, the decline of Red Knots. The presence of horseshoe crabs is indicative of a healthy and balanced coastal ecosystem.

3. Summer Flounder

Nicknamed “chameleons of the sea,” summer flounder are a kind of flatfish that have evolved to live on the bottom of the ocean and can change their coloring to camouflage with their surroundings. They’re born with an eye on each side of the head, but as they mature, one eye migrates to the other side, so both eyes face up. They rely on the littoral zone in their juvenile stage, burrowing into the sediment of marsh creeks, seagrass beds, mut flats and open bays. Because this life stage takes place near heavily populated areas, maintaining good water quality is essential for the health and survival of these fish.

Joseph Bartholomew Kidd, CC0, via Wikimedia Commons

4. Sea Grass

Seagrasses are submerged plants that often live in the littoral zone, where water is shallow and light can penetrate. They provide many important ecological services, including creating habitat and shelter for a diversity of marine organisms, oxygenating the water, nutrient cycling, and slowing the flow of water. Their roots trap sediment, which helps improve water quality and also reduces erosion by stabilizing the coastline. Seagrasses can also help water quality by absorbing nutrients in runoff from the land.

5. Harbor Seal

These coastal seals rely on the littoral zone as a place to congregate, “hauling-out” onto the shore to rest, avoid predators, thermoregulate, and reproduce. They play a key role in maintaining the balance of the food web and contribute to nutrient cycling through feeding habits. They also serve as an indicator of ecosystem health.

6. Knobbed Whelk

Knobbed Whelks are large, predatory sea snails that live in Atlantic tidal estuaries. They spend summer and winter in deep water, and spring and fall in shallow intertidal flats, where they feed on oysters and clams. During their spring and fall migrations, they breed in deep water, laying a string of eggs, nicknamed a “mermaid’s necklace.” Their young provide an important food source for crustaceans, horseshoe crabs, and fish. Adult whelks are consumed by loggerhead sea turtles and humans, who also prize their beautiful shells.

7. Ruddy Turnstone

Like Red Knots, Ruddy Turnstones rely on the littoral zone throughout their lifecycle. These plump sandpipers migrate long distances between their breeding grounds in Arctic tundra and their off-season grounds along the coasts of North and South America, Eurasia, Africa, and Australia. Because their migration touches so many places, they serve as important indicators of ecosystem health across the globe.

8. Striped Bass

Striped bass, like many other species, rely on the littoral zone as a nursery. Native to the Atlantic coast, they migrate between fresh and salt water at different points in their life cycle. They spawn in freshwater, and their larvae drift downstream to river deltas and the shallow waters of coastal estuaries. They spend 2-4 years there, before moving out to the Atlantic Ocean. Striped bass play an important part in the food web.