The tidepools along the San Mateo County coast are filled with hidden treasures. With a little planning, you can pay a visit to an ecosystem teeming with marine life and get up close and personal with the beautiful sea creatures that only low tides reveal.

Tidepools are part of a tidal zone ecosystem consisting of a splash zone, high-tide zone, mid-tide zone, and low-tide zone. Different animals and algae have adapted to the fluctuating conditions these zones offer, and they have turned the tidepools and surge channels into their homes.


The splash zone is covered only by the “highest high tide” each day (there are two high tides and two low tides each day on our coast—more on tides later) and this zone is dry three-quarters of the day.

Who lives in this zone and how do they survive?

Periwinkles – Periwinkles are very tiny black snails. They resist drying out when the tide is out by pulling their soft bodies into their shells and tightly closing their shells with a “door” – the operculum. Then they produce mucus that acts as “glue” to stick them in place on rock.

Limpets – Limpets hold on to rocks so tightly that attempting to remove them will result in a broken shell. The limpet does not have an operculum like a snail, so it makes a “home scar,” a slight depression shaped exactly like its shell, to seal itself tightly to the rock.

Acorn Barnacles – Barnacles cement themselves head first to a spot on a rock next to others of their kind. They secrete hard protective “plates.” When the water covers them at high tide, they open the shell doors and stick out their feathery feet to filter feed!


The high-tide zone is covered by water during the two high tides that we have each day. The creatures in this zone are dry half of the day and covered in water the other half of the day.

Who lives in this zone?

Black Turban Snails – Black turban snail shells are blue-black in color on top and silvery white near the opening. They have an operculum that can cover the opening, just like the periwinkle snail, to keep them from drying out.

Hermit Crabs – Hermit crabs often use the shells of Turban snails for their home. They are the clowns of the tidepools as they often fight with each other as they scavenge for food. They scurry under rocks and algae to keep moist.

Mossy Chitons – Chitons are mollusks, like snails and limpets, but their shell is divided into eight “plates.” If a chiton is dislodged from its tight hold on a rock, it will roll up like a cradle (or a Roly-Poly bug).

Green-lined Shore Crabs – Shore crabs scurry into cracks or under rocks to hide from predators and waves. They are able to spend much of their time out of water.


The mid-tide zone is left dry only during the lowest low tide, which happens once a day. It is covered by water three-quarters of the time.

Who lives here?

Aggregating Anemones – These sea anemones reproduce themselves by cloning. Their tentacles contain stinging cells that stun their prey as it floats, swims, or crawls by. At low tide, these anemones pull in their tentacles and become a lump covered with bits of sand, shell, and rock to reduce water loss.

Tidepool Sculpins – These small fish (also called “tidepool Johnnies”) are well camouflaged and will quickly dart for cover under rocks or algae in the tidepool.

Bat Stars – Bat sea stars have arms that are webbed like the wings of a bat, with a scaly appearance. Sea stars eat by pushing their stomachs out of their bodies in order to digest their prey. Sea stars have an elaborate system of tube feet that work like suction cups.

Nudibranchs – Nudibranchs are sea slugs—snails without shells. They are brightly colored and are often called the “butterflies of the sea.” They hold on to algae, surf grass, or rock in the tidepools.

California Mussels – Mussels have two shells (called bi-valves) and secure themselves to the rocks by very strong hair-like fibers.


The low-tide zone is exposed for only a few hours every few weeks at special “minus” tides. This is the very best time to visit the tidepools.

Who lives in this zone that is usually underwater?

Purple Sea Urchins – Sea urchins are related to sea stars. They are round and covered with purple spines. They scrape their spines against rock to carve out depressions in which to make their homes.

Giant Green Anemones – Anemones are known as the flowers of the sea, and the giant green is one of the most beautiful. Its brilliant green coloring is due in part to symbiotic algae that live within the tissues of the anemone. They are one of the largest anemones in our tidepools and are very long lived. An anemone 8 inches across could be 75 years old!

Kelp Crabs – Kelp crabs hide beneath thick layers of kelp and surf grass. Their shell (carapace) is shaped like a shield, and they have long spider-like legs.

Red Octopus – One of the most amazing creatures in the tidepools is the small red octopus. It is less than a foot long, and it can be found tucked beneath rocks or lurking beneath seaweed in tidepools or found crawling between tidepools! Octopuses can be out of water for only a few minutes at a time.


Tides are caused by the gravitational pull of the moon and the sun. Although the moon is much less massive than the sun, it is a lot closer to the earth, with the result that the moon’s influence on the tides is a little over two times greater than the sun’s. Sometimes the sun and the moon can join gravitational forces, and all that gravitational pull can create some really high and low tides.

Each year around January 2, earth, in its elliptical orbit, is closest to the sun; and the sun’s gravitational pull on earth and earth’s water is strongest. The gravitational pull of the moon combines with the gravitational pull of the sun when the moon’s position is such that the earth, sun, and moon are aligned in a straight line or nearly so. This creates the highest high tides and the lowest low tides of the year. The exact dates vary each year because it depends on where the moon is in its orbit. We often get these super-high/low sun-plus-moon tides (also called King Tides) in December and January. (When the earth is at the point in its orbit that is farthest from the sun, around July 2, and the moon is aligned just right, we also get super-high and super-low tides.) Super-high tides can give us a preview of sea level rise and help us identify areas that are prone to submergence. And when the tide goes out, super-low tides are a great opportunity to go tidepooling!


When you are ready to visit the tidepools, look for dates with a nice, low tide—something below +1.0 feet is generally pretty good, depending on the site. To time your visit, it is helpful to look at a tide table or graph of the predicted height of the tide throughout the day. (These can be found by searching the Internet.) You’ll see plenty of tidepool action during a +1.0-to-0.0-foot tide; but extra-low, negative tides reveal more rocks and more creatures that are usually submerged.

To best enjoy your time tidepooling:

  • Bring warm clothes and closed-toe shoes. Rubber boots with a rugged sole are best (seaweed is slippery). A magnifying glass or hand lens can also be helpful.
  • Keep your eye on the ocean, and look up and look around often so the tide doesn’t sneak in on you.
  • Remember that creatures in tide pools are for looking at, not prodding at or even touching at all. Even though they’re battered by waves on a daily basis, tide pool organisms are vulnerable to disturbance by humans. A curious poke could mean death for a tide pool animal.
  • Purchase or borrow a local field guide, if you want to identify the incredible sea treasures you are seeing.
  • Plan to arrive at the tidepool at least one hour before low tide so that you have plenty of time to explore before the tide starts coming back in.

The following are great spots to enjoy tidepooling along our coast:

  • Fitzgerald Marine Reserve (the reef just north of Seal Cove beach is especially good)
  • Pillar Point Harbor (the reef where the Maverick’s wave breaks)
  • Bean Hollow State Beach (just south of the north parking lot near Pebble Beach)
  • Pigeon Point Lighthouse (on the north side of the lighthouse parking lot)
  • Pescadero State Beach (by the south access parking lot)
  • Scott Creek (although this area is in Santa Cruz County, it is just 8 miles south of Año Nuevo State Park; the reef is north of the creek)

Happy tidepooling and have fun hunting for sea treasures!