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Sandy Shore Ecosystem

There are many different types of shorelines, but when many of us picture the beach, it is sandy. The sand is where we dig holes, build castles, and lie on our towels to enjoy the sunshine. There are many other organisms that enjoy that sandy habitat also. You may have seen marine mammals such as harbor seals (Phoca vitulina) or sea lions (Zalophus californianus) resting on the sandy shore or rocky outcroppings, but not all sandy beach organisms are so obvious. Some are well camouflaged or hide in the sand, so you may not even know they are there. Some even come under cover of the night.

One of the most fascinating visitors to the sandy beach ecosystem is the grunion (Laureshtes tenius). From March to August during nighttime, high tides caused by a full or new moon, these fish will swim up onto the beach and strand themselves to spawn. The female will dig herself into the sand using her tail, and then deposit her eggs two to three inches below the surface. The males swim all around her, depositing their milt (which contains their sperm) on the sand, where it flows down the body of the female and fertilizes the egg. The fertilized eggs will incubate for about two weeks, safe under the sand until the next high tide washes them out. These spawning events can turn into huge spectacles with thousands of fish on the beach at once, which can sometimes draw large crowds of observers.

Beaches in our area which have had Grunion runs include San Clemente Pier Beach, Doheny State Park, Corona del Mar State Beach, and Newport Municipal Beach.

Photo Courtesy by California Beaches

If you have been to the beach, you have undoubtedly seen shorebirds. From the ubiquitous Gulls (genus Laurus) to the shy Sanderlings (Calidris alba), the sandy shoreline provides a habitat for many birds. Some birds, like the endangered California Least Tern (Sternum antillarum browni) and the Western Snowy Plover (Charadrius alexandrinus nivosus) make their nests right in the sand and raise their chicks on the beach. Others, such as Spotted Sandpipers (Actitis macularius) and Egrets (Adrea alba) come to the beach to find food. While a gull would be happy with the leftovers of your sandwich, many shorebirds such as the various sandpiper species are looking for tasty treats buried in the sand.

Sandpiper using their long beak to forage for food deep in the wet sand.

The long beaks of these shorebirds can probe deep into the substrate where the burrowing organisms they are looking for try to hide by digging into the sand. This doesn’t always work, and sometimes the digging creates clues as to where they are hiding. You may have seen dozens of little V-shaped patterns in the receding tide as you walk out to the surf. These are made by one of the most well-known of the sediment dwellers, the sand crab (Emerita analoga). Children love to dig for sand crabs and watch them burrow back into the sand. This burrowing behavior is part of their feeding strategy. When a wave washes up the beach, the sand crabs come out of their burrows and extend their feathery antennae to try to capture food particles suspended in the water. As the water flows back down the beach, they must again burrow into the sand to avoid predation. As they are feeding this way, they get moved slowly down the beach with the current.

Shore crabs popping their heads out of the sand to feed | Photo Courtesy by Monterey Bay Aquarium

Clams also leave clues to their location under the sand. If you see a dimple or small hole in the sand after the water has washed out, you might be looking at evidence of a clam. These holes, called clam shows result from the clam digging into the sand and squirting out the water that they absorbed during the digging process. In Orange County, you might find razor clams (Siliqua patula), pismo clams (Tivela stultorum), or littlenecks (Leukoma staminea). These were an important source of food for the indigenous people who originally inhabited these lands. Deeper in the sand dwell blood worms (genus Glycera), nature’s sand cleaners.

They eat the sand that they burrow into and their bodies digest the organic material coating the sand grains. The clean sand is then deposited back on the beach. These worms can be found at the mid-tide level where the sand is slightly pockmarked and has a different consistency.

Photo Courtesy by Washington Department of Fish & Wildlife

These burrowing animals live in the swash zone, the area where the waves actively wash back and forth across the beach. A bit farther up the beach, we can find other burrowing animals that live in a very special microhabitat on the sandy beach. Beach wrack, the name given to piles of seaweed that lie along the high tide line, is an extremely important component of the sandy beach habitat. Beach wrack is like the ocean’s daily Grub-Hub delivery for the shoreline. The wrack is the main source of vegetation in this ecosystem, so it forms the basis of a large food web. In addition to kelp, the wrack also brings in tiny organisms and decaying matter from the sea. Two very common wrack inhabitants are beach hoppers (Orchestoidea californiana), small crustaceans often called sand fleas, and isopods (Excirolana kincaidi), which are similar to the roly-polies that we find in terrestrial settings. These, as well as kelp flies (Coelopa frigida), rove beetles (family Staphylinidae), and sometimes crabs and other small crustaceans, break down the wrack and pass its nutrients up the food chain. These tiny animals burrow under the beach wrack during the day to avoid predation and keep from drying out.

Unfortunately, many Orange County beaches actually remove this beach wrack when they “groom” the beaches. Beachgoers do not like the smell of decaying beach wrack and do not appreciate the beach hoppers and kelp flies that live there; sand flies bite, and can raise a nasty welt or even a blister. But this can have powerful negative effects on the sandy beach ecosystem. Without the beach wrack, food supplies for shorebirds are severely diminished, and an entire microhabitat is destroyed. In fact, a California Sea Grant study from 2019 showed that urban beaches contain 50% fewer species than their non-urbanized counterparts. The wrack also plays a role in establishing dunes on the beach. It can trap windblown sand and anchor it in small hummocks and dunes. These dunes play an important role in protecting areas behind the beach from storm surges and coastal flooding.

Snowy plover on the hunt for food in and around the beach wrack.

The beach is truly a treasure trove of beautiful and fascinating organisms. From adorable marine mammals that come to the shore to rest or give birth, to the tiny sand fleas that we try to avoid, all of these organisms have an important place in the ecosystem. So, next time you are walking down the beach and see a pile of beach wrack crawling with beach hoppers and kelp flies, look at it as an integral part of this very special and sensitive habitat.

To learn more about the shifting sands on our beaches, the preservation of watersheds and wildlife, the effects of rising sea levels, and more check out our Coffee & Conservation below on Sand Movement!

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