Get ready to be amazed when you visit the tidepools.
But first,
let’s learn about the tidal zones.
The intertidal ecosystem is at the edge of land and sea, shifting with the movement of the tides. There are four distinct zones with different characteristics in the intertidal area, as well as a subtidal zone that is slightly lower in the ocean. Intertidal zones also vary in levels of predation, interspecies competition, temperature stress, desiccation (drying out), and salinity. Each zone is populated by various species depending on their tolerance of exposure to water, air, or physical stressors like heat shifts. For example, mussels are limited to the mid and low intertidal zones due to their vulnerability to drying out in air.
As the tide withdraws, it can also leave tidepools behind in pockets of rock formations. These serve as a refuge for any animals that are not adapted to remaining out of the water, such as sea stars, nudibranchs, or small fish.
Spray/Splash Zone
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The spray zone is the highest area, just above the water level at high tide. It receives mild water exposure from waves splashing and sea mist. Organisms here require adaptations to resist high temperatures in the summer and cold in the winter. Under spring tide ("King Tide") or storm conditions, this zone may temporarily be underwater.
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Striped Shore Crab
Periwinkle Snail
High Zone
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The high zone remains in the open air for most of the day but is covered by water at high tide. It is populated by aquatic life that can withstand more exposure to the elements, including crabs, chitons, and limpets. In Southern California, this zone is often indicated by the presence of larger acorn barnacles (Balanus glandula).
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California Mussel
Purple Urchin
Mid Zone
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The mid zone alternates between being submerged and being above water multiple times in a day. Organisms in the mid zone must be firmly rooted in place or flexible to not be battered by the energy of the waves. This zone is also characterized by swaths of rockweed and mussels, which help form shelter for other creatures.
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Chestnut Cowrie
Hermit Crab
Ochre Star
Black Turban Snail
Low Zone
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The low zone is typically covered by water, except for brief exposure to the air during low tide. Temperature fluctuations are mediated by the water, such that conditions underwater remain more consistent. Red and brown algae can be found in the low zone, as well as a greater number of aquatic animals like shrimp, snails, nudibranchs, anemones, and sea hares. The higher water level in the low zone means these animals are in less danger of desiccation or temperature shock.
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Chiton
Sea Cucumber
Sea Hare
Brittle Stars
CA Spiny Lobster
Two-Spot Octopus
Bat Star
Anemones
Tidepool Sculpin
Subtidal Zone
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The subtidal zone lies just below the intertidal ecosystem. It is continuously underwater unlike the intertidal zones but remains shallow in depth. Due to a constant layer of insulating water, the temperature and light exposure levels of this zone are mediated and remain more consistent. Larger aquatic animals like fish and octopuses are more common in the subtidal zone.
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Opaleye
Garibaldi
Abalone
Splash Zone
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Pachygrapsus crassipes – Like all crustaceans, these crabs have gills, but they can survive out of water for up to 70 hours. They have been known to eat everything in the intertidal, including their own species. They can be found throughout all zones of the intertidal, but are usually resting in shady cracks and crevices.
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Littorina spp. – These tiny snails are often mistaken for eggs or rocks. During the low tide, the snails seal the water inside their shells with a trap door called an operculum. Their shells become the first home for juvenile hermit crabs.
High Tide Zone
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Mytilus californianus – Mussel beds form a very important habitat for more than 300 marine species. These filter feeders have numerous natural predators such as sea stars, shore birds, and sea otters, but often are disturbed and collected by humans for bait and aquaria, or killed by incidental trampling.
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Strongylocentrotus sp. – The purple urchin feeds primarily on brown algae that gets stuck on its spines in tide pools and often concentrate their efforts on the holdfast of the kelp when in the ocean. Although purple sea urchins are smaller than their less common counterpart the red sea urchin, both are commonly served in Japanese restaurants as uni.
Mid Tide Zone
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Neobernaya spadicea – The chestnut cowrie is named for its beautiful chestnut-colored polished shell. These snails are the only cowrie found in the east Pacific Ocean. Often hiding under rocks and protected crevices, these creatures are carnivorous eating sea anemone, sea sponges, and other dead organisms.
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Pisaster ochraceus – The ochre star is the most common sea star in the intertidal. It can eat anything that can’t move out of the way including snails, barnacles, chitons, and mussels. Identified as a keystone species, ochre sea stars allow for a diverse rocky marine intertidal. Its only known predators are sea otters and gulls.
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Chlorostoma funebralis – Like other snails, Black Turban Snails use a scraping tongue called a radula to eat algae growing on the rocks. Black Turban Snails are a eaten by crabs and birds, and their shells are a favorite for hermit crabs.
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Pagarus spp. – Hermit crabs are a unique animal because they use the discarded shells of intertidal snails to protect themselves from exposure. They will change shells as they grow, often keeping an eye out for new empty shells, but have been known to steal shells from other hermits. As a defense, they will draw their legs into their shells and fall to the bottom of their tidepool.
Low Tide Zone
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Parastichopus spp. – Sea cucumbers look like sea slugs, but are actually closely related to sea stars and urchins. It has one of the most unique defense mechanisms of all tidepool creatures. When in extreme danger, it will eject its internal organs in an effort to distract its predator. If it survives being eaten, it can regenerate these organs!
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Panulirus interruptus – Unlike Maine lobsters, California spiny lobsters do not have huge front claws. Instead, all their appendages are used for walking. They shed their exoskeletons periodically as they grow, and their molts can be found along the shoreline. These lobsters will hide in crevices during the day and move around at night feeding on sea urchins and mussels. A few predators of the spiny lobster are the California sheepshead, sea bass, and sea otters.
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Anthopleura spp. – Anemones are related to jellies and corals and have small stinging cells in their tentacles known as nematocysts. They adapt to surviving exposure during low tide by collecting shell fragments to remain moist. They have a symbiotic alga living within their cells that provide supplemental nutrition and oxygen.
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Mopalia muscosa – Chitons like this mossy chiton, are snail-like mollusks. They have a single muscular foot, and 8 jointed shell plates. It stays in one place during the day leading visitors to assume that they are fossils, but at night they move and graze on algae growing on the rocks.
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Aplysia Californica – Sea Hares are named for their broad antennae that look like a hare’s ears. They are herbivores, so they eat red, brown, and green algae. They can release a dark purple ink if disturbed or irritated. They have been observed to lay almost 480 million eggs in one season.
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Ophiuroidea – These small sea stars spend the day hiding under rocks and crevices such as mussel beds. They can also be found in the holdfasts of giant kelp that have washed up on shore. They are scavengers where they will eat decaying matter or plankton.
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Octopus bimaculoides – Living only 1 to 3 years, the two-spot octopus can change color instantly using specialized cells called chromatophores. It can drill into their shelled prey using a scraping tongue called a radula. The two spots below the eyes of the octopus act as eyes to distract predators. Studies show that they have the intelligence of a 3-year-old human!
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Patiria miniata – Bat stars are named for their webbed arms. They come in a huge variety of colors and can have mottled patterns. They eat algae and animals, both dead and alive. Other sea stars, mollusks, and crustaceans will feast on these bat stars.
References:
Intertidal. National Parks Service. 2016 May 13 [accessed 2021 Jan 31]. https://www.nps.gov/subjects/oceans/intertidal.htm
National Geographic Society. Intertidal Zone. National Geographic. 2019 Oct 10 [accessed 2021 Jan 31]. https://www.nationalgeographic.org/encyclopedia/intertidal-zone/
National Oceanic and Atmospheric Administration. What is the intertidal zone? NOAA's National Ocean Service. 2020 Apr 9 [accessed 2021 Jan 31]. https://oceanservice.noaa.gov/facts/intertidal-zone.html
Rosaler J. Orange County Tidepool Docent/Educator Training Manual. 2008.
Töpke K. Rocky shore habitat. Coastal Wiki. 2020 Sep 8 [accessed 2021 Jan 31]. http://www.coastalwiki.org/wiki/Rocky_shore_habitat
