California’s Ocean Habitats: The Rocky Intertidal Zone

Imagine a mystical world revealed when the gravitational forces from glowing celestial orbs peel back watery waves, uncovering pools teeming with life. Jewel-toned, flower-like animals gently sway in the currents, waiting for their next meal to float by. Eight-armed creatures turn a kaleidoscope of colors to camouflage into their surroundings. Botanical gardens of iridescent tendrils stretch out like feathery tree branches across the surface of the pools.

Would you like to visit and explore this alien world? Well you can, right here on Earth, in a habitat called the rocky intertidal zone. Grab your beach attire and supplies and let’s head out to the coast to go tidepooling!

The first, and probably most important information you need to know is that tidepools are sensitive habitats. Although tidepools have evolved to thrive in the harsh conditions of the coastal ocean, they can easily be damaged by overzealous visitors. When visiting tidepools it is important to practice proper tidepool etiquette and responsible harvesting. Here are some useful tips:

  • If you plan to collect your next meal from the rocky intertidal zone, know your local marine protected area and tidepool harvesting regulations, and current health advisories before you head out to harvest. Be sure that anyone 16 years old or older has a current recreational fishing license and, if south of Point Arguello (Santa Barbara County), an Ocean Enhancement Validation.
  • While tidepooling, avoid picking up organisms, and touch gently with just two fingers.
  • Watch your step! Be careful to avoid slipping and trampling on the tidepool life.
  • Never turn your back to the ocean! Even on calm days, sneaker waves can wash ashore.

After learning how to protect tidepools during your visit, the next thing you need to know to start your tidepool adventure is when the tide will be low enough to visit this unique habitat. The tides on Earth are largely influenced by the gravitational pull from the moon and sun. On the California coast, there are usually two high tides and two low tides every 24 hours. Because the phase and positions of the earth, moon, and sun are predictable, so are the tides! You can find your local tide table predictions here or by picking up a pocket tide table booklet at any of your local ocean recreational businesses. There are even tide prediction apps for your smart phone. Plan to arrive about an hour before the lowest tide during the day and aim for tides lower than 0.0 feet. The lower the tide, the more tidepool habitat there will be to explore.

The rocky intertidal zone is one of the most extreme places to live on the planet. The animals, plants, and seaweeds that call the tidepools home endure large changes in temperature, weather conditions, and the pounding surf as the tides ebb and flow. Imagine if you were sitting comfortably in your living room and it suddenly started to fill up with water! To stay alive, you would have to learn how to hold on, breathe, and find food in this changing environment. Right when you get the hang of it, the flood subsides and you are left sitting back on your sofa, high and dry.

The constantly changing environment in the rocky intertidal creates a common ecological pattern called zonation. Zonation happens in many places in nature, such as forests, mountains, and marshlands. However, zonation in the rocky intertidal is unique because it occurs on such a small scale. Exploring the different zones on a mountain could take many hours or even days of hiking to get from the forest lands at the mountain base to the snowy habitats above the tree line at the top. However, in the rocky intertidal you can traverse zones just by taking a few steps, making it a wonderful place to easily discover and study different environments. Many pioneering scientific discoveries about how ecosystems adapt to changing environments and disturbances have been made in the rocky intertidal zone.

illustration of intertidal zones
The ecological pattern called zonation in the rocky intertidal at Pigeon Point. There are three main zones: high, mid, and low.
photo by M. Worden.

The rocky intertidal is split into three main zones: high, mid, and low. The high zone is exposed first as the tide goes out, so the organisms that live there are better adapted to a life on land. You may find seaweeds like rockweeds that help shelter tiny snails from the sun and wind while the tide is out. Unlike most land snails, the snails that live in the rocky intertidal have a trapdoor-like structure, called an operculum, that they close tight to prevent from drying out during low tide.

As you make your way closer to the water you enter the mid zone, and more life begins to appear. Remember to tread lightly and avoid stepping on any organisms and slippery rocks, and never turn your back to the ocean. Tidepools in the mid zone harbor bright green anemones, lace-like red seaweeds, and prickly purple sea urchins. Small fish called sculpins dart around in the pools gulping up tiny crustaceans. Mussels take up much of the rocky real estate in the mid zone and form expansive beds that act as an important habitat for many intertidal organisms. They attach to the rocks and each other using powerful sticky structures called byssal threads that keep them from getting swept away by the waves.

Mussels are the favorite food of one of the most charismatic intertidal creatures that you may be lucky enough to find, the ochre sea star. The ochre sea star is a fierce predator that has a unique way of eating its meals. It pries apart the two shells of a mussel using thousands of tube feet and pure brawn, then spits out its stomach to engulf what’s inside the mussel, sucking its stomach back in once it’s digested its meal. The ochre sea star is considered a keystone species because it plays a critical role in the intertidal ecosystem. With its voracious appetite, it controls mussel populations and clears more space on the rocks for other organisms to live, boosting the biodiversity in the rocky intertidal.

Sea star populations on the U.S. West Coast saw a huge decline from 2014 to 2016 due to sea star wasting syndrome, which coincided with the “warm blob” and a strong El Niño year that heated up ocean waters. Through the statewide MPA Monitoring Program, researchers surveying sea star populations were able to detect the onset of the decline early, and continue to monitor sea star recovery and the effects of this die-off on the rocky intertidal habitat.

The sea star die-off is just one example of how the changing climate is affecting tidepool habitats. Warming, more acidic waters, and rising seas impact tidepool habitats in many ways, like causing species to move north and shrinking living space across each intertidal zone.

A quick glance at the time indicates that it’s almost low tide, and time to leave the mid zone behind and step into the low zone. The low zone is only exposed for a short amount of time before the tide starts to come back in, so keep an eye on the waves.

The colorful world of the low zone is accented by bright orange sponges, hyper-colorful sea slugs called nudibranchs, and glimmering, iridescent seaweeds. You may have to gently move the long, frilly fronds of the feather boa kelp to uncover animals and seaweeds living beneath the blades. Feather boa kelp does not grow as fast as giant kelp, but it covers many of the low zone rocks. Peek under the rocks, being careful not to move them, and you may see a monkeyface prickleback peering back at you or the curly arms of an octopus reaching out from a dark crevice.

The only flowering plant found in the rocky intertidal, surfgrass, is considered an ecosystem engineer because it can change its surrounding environment by trapping sediment, dampening wave action, and changing carbon dioxide into oxygen when it photosynthesizes.

researchers in intertidal zone
Researchers monitor the biodiversity in the rocky intertidal at Del Mar Landing State Marine Reserve as a part of the statewide MPA Monitoring Program.
photo by D. Lohse, MARINe

Today, the rocky intertidal continues to play a critical role in marine science as a key habitat for research and monitoring in California’s Marine Protected Area (MPA) Network. Studying the rocky intertidal can give us important information about marine biodiversity, or variety of species, and the effects of climate change on our coastal communities.

About 27 percent of California’s rocky intertidal habitat is protected within MPAs. To enhance your tidepool experience, consider visiting MPAs that were designed to protect this important habitat. Cabrillo State Marine Reserve, Point Lobos State Marine Reserve, and Duxbury Reef State Marine Conservation Area are all excellent MPAs for exploring the intertidal zone. Many MPAs, like Montara State Marine Reserve, have docent programs that lead scheduled tidepool tours and teach visitors the proper tidepool etiquette. Check your local websites and guidebooks for more information on the best beaches to find tidepools near you.

Before you know it, the ocean begins to rise and reclaim the rocky intertidal zone as part of the watery realm, and it’s time to head home. But your intertidal adventure doesn’t have to end when you leave the rocks! Besides visiting the tidepool habitats in your local MPAs, here are some resources about tidepools and ways you can help conserve this important habitat for exploration when the tide goes out again:

Each visit to the rocky intertidal zone will reveal new and fascinating wonders about this alien world, so keep your tide calendar handy!

post by Sara Worden, CDFW Environmental Scientist