Sand, no matter where in the world you are, is primarily made up of the same components: tiny pieces of different rocks and minerals that lead to sand having different colors and compositions. The main one found here in California is tiny crystals of mineral quartz – which consists of silica and oxygen, the most common elements in the Earth’s crust.


Sand from Texel, Netherlands photographed with darkfield illumination. Image courtesy of

Some creatures that live in the sand (Bolsa Chica and elsewhere) & a little bit about them…

What do they eat?

They obtain their nutrients to survive from the passing waves via an antennae they extend that collects detritus and plankton.

Where do they live?

They spend most of their adult lives in the sand between the surge zone, that space where the waves move up and down. To be able to survive such a rough environment they have some adaptations that help them survive and thrive.

Starting with their tough, rounded exoskeleton on top that defects the force of crashing waves. On the underside of mole crabs they have 5 sets of legs that help them move backwards and a V shaped digging tool called a telson, at the rear of their body that faces forward and helps them anchor in the sand/dig rapidly and protect their underside. All of these are necessary adaptations to survive those speedy waves brute force! Interestingly, females are larger than males and the majority of mole crabs live in colonies that can be spotted when waves retract as as v shaped outlines in the sand toward land. As the waves directions change mole crabs change direction as well to ensure they are in a good position to use their antennae to feed.

How long do they live?

These creatures live short lives, 2-3 years, and mate in late spring/early summer. A female can produce up to 40,000 eggs at a time that are kept under the telson for about a month. The eggs start off bright orange and then change to brown as time passes. Once eggs hatch they go through several morphing stages before joining a colony and looking like the common mole crab. These mole crabs make excellent food for many fish and bird species which is why fishermen sometimes use them as bait and they are even eaten by humans in some places.

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Sand fleas – also known by their common nickname the chigoe flea. They hardly get bigger than 1 millimeter so they are quite difficult to see. They are common residents found in California deserts and beaches who feast on blood by burrowing under the first layer of skin.

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These creatures are classified as Bivalves – meaning their bodies are laterally compressed and enclosed by a shell consisting of two hinged parts – and there is a wide variety of clams and mussels found in the SoCal sand. One such clam is the Pacific Littleneck Clam (Leukoma staminea).

How do they eat?

These little guys are what is known as filter feeders. Water goes through the clam and anything edible like microscopic algae or detritus gets digested by the clam, and the rest gets filtered through and sent back out through the siphon.

On the other hand, who eats clams?

Good question! Fishes, marine mammals, birds, and humans are among the top predators of clams. PSP or paralytic shellfish poisoning is something that can occur and be dangerous to all predators of clams. This occurs when some of the microscopic food ingested by the clam contains neurotoxins which accumulate in the clams as it eats more and more. PSP is less common from little neck clams versus other clams because they have an enzyme that converts the neurotoxin into a less dangerous chemical. In terms of competition their biggest competitor is the Japanese Littleneck Clam.

How did fiddler crabs get that funny name?

Well, fiddler crabs – also known as calling crabs – have one distinctively large and small claw. However that is only on the male crabs, the female crabs have the same size claws. The claws are scientifically known as chelipeds. If the big claw is lost the opposite claw grows in size to replace that big claw after a few molts. Crabs communicate via moving their claws in patterns and gestures. They get the name fiddler crabs because they hold the large claw in front of their body and move it back and forth thus giving the illusion of playing the fiddle.

You may be wondering “how do they eat”?

The (small) claw (on males) picks up sediment and puts it in its mouth where the crab uses maxillipeds and other parts of its mouth to sift through and find anything edible (like algae). Then, the rest of the sediment get spat up as sediment balls also known as feeding pellets. It is believed that the feeding habits of crabs plays a vital role in wetlands by introducing air to the substrate.

What are the parts of a crab called?

How do fiddler crabs reproduce?

After mating and courtship displays involving waving of the unevenly sized claws of males, the female crabs keep their eggs on the underside of the belly. She stays in her burrow for 2 weeks and then heads out to drop her eggs into the tide. Fiddler crabs are found all over from mangroves to beaches, from Africa and Portugal to the USA.

Bolsa Chica is home to several species of terns, including Royal Terns (Thalasseus maximus), Elegant Terns (Thalasseus elegans), Forester’s Terns (Sterna forsteri), Caspian Terns (Hydroprogne caspia) and the endangered California Least Tern (Sterna antillarum browni). Terns are closely related to gulls, though differ slightly from everyone’s favorite (or least favorite) beach bird. These birds utilize the sand in an interesting way: as nesting grounds.

How do terns reproduce?

Terns have an elaborate courtship ritual for mating that can take place in the air or on land:

    • Royal and Forester’s Terns use what is called the fish-flight display. During this display, a male flies around with a fish in his beak while being pursued by a female. This chase is very vocal and the birds weave through the sky dramatically, sometimes descending together and other times gliding in sync.
    • Elegant Tern courtship displays take place on the ground, where both members of a pair droop their wings, stretch neck upward, and raise and lower their bills
    • Caspian Tern males capture fish and fly back and forth by groups of other terns, showing off their prize. Small groups of both males and females may follow or chase the male in the air. He will eventually land next to her and present her the fish; a receptive female will accept the fish.
    • California Least Terns court on land, where he male carries a fish in his beak while dancing around a female, and if she chooses him she begins to dance with him.

All of these rituals lead to monogamy for the season.

Tern eggs vary in color as the sand and/or gravel they lay their eggs in varies from one site to another, as so does the down of the chicks that hatch. Eggs can be blonde with brown or gray speckles and sometimes even reddish to best match the terrain (to best camouflage eggs from predators). While a good disguise is necessary to avoid predators, unfortunately this camouflage can sometimes be too good and lead to humans stepping on hidden eggs if they are not in a fenced off area.

What are terns conservation status?

Terns were previously on the endangered species list, but some species have been removed thanks to conservation efforts. Royal, Forster’s, and Caspian terns are currently species of low concern, with their numbers remaining stable or increasing over the last few decades. Elegant Terns are still listed as vulnerable/near threatened, despite a northward increase and spread in California, as their nesting is restricted to very few sites. California Least Terns have been listed as federally endangered in 1970, and endangered at the state level in 1971; these birds are at high risk of population decline through natural disasters, predation, and human disturbances.

To help with the conservation efforts of the California Least Tern, the Bolsa Chica Conservancy hosts Eyes On Nest Sites (EONS), which monitors local populations of California Least Terns and Western Snowy Plovers during breeding season. Click here to learn more about EONS!