Tide pools are rocky pools by oceans that are filled with seawater. Many of these pools exist as separate entities only at low tide.

Tide pools are habitats of uniquely adaptable animals that have engaged the special attention of naturalists and marine biologists, as well as philosophical essayists: John Steinbeck wrote in The Log from the Sea of Cortez, "It is advisable to look from the tide pool to the stars and then back to the tide pool again."

The life in tide pools

Tide pools provide a home for hardy organisms. Inhabitants must be able to cope with a constantly changing environment — fluctuations in water temperature, salinity, and oxygen content. Huge waves, strong currents, exposure to midday sun and predators are only a few of the hazards that tide pools' animals must endure to survive.
Waves can dislodge mussels and draw them out to sea. Gulls pick up and drop sea urchins to break them open. Starfish prey on mussels and are eaten by gulls themselves. Even black bears sometimes feast on intertidal creatures at low tide. Although tide pool organisms must avoid getting washed away into the ocean, drying up in the sun, or getting eaten, they depend on the tide pool's constant changes for food.

Tide pool zones, from shallow to deep

Spray/splash zone

This zone receives spray from wave action during high tides and storms. At other times the rocks experience other extreme conditions, baking in the sun or exposed to cold winds. Few organisms can survive such harsh conditions. Lichens and barnacles live in this region. In this zone, different barnacle species live at very tightly constrained elevations. Tidal conditions precisely determine the exact height of an assemblage relative to sea level.

Since the intertidal zone periodically desiccates, barnacles must be well adapted to water loss. Their calcite shells are impermeable, and they possess two plates which they slide across their mouth opening when not feeding. These plates also protect against predation.

High and mid tide zone

The high tide zone is flooded for hours during each high tide. Organisms must survive wave action, currents, and exposure to the sun. The high tide zone is inhabited by sea anemones, starfishes, chitons, crabs, green algae, and mussels. Marine algae can provide shelter for such organisms as nudibranchs and hermit crabs. The same waves and currents that make the life in the high tide zone so difficult bring food to the filter feeders and other intertidal animals.

Low tide zone

This subregion is mostly submerged — it is exposed only during low tide. This area is teeming with life; this subregion's most notable difference from the other three is that there is much more marine vegetation, especially seaweeds. There is also greater biodiversity. Organisms in this zone generally are not well adapted to dryness and temperature extremes. Low tide zone organisms include abalone, anemones, brown seaweed, chitons, crabs, green algae, hydroids, isopods, limpets, mussels, nudibranchs, sculpin, sea cucumber, sea lettuce, sea palms, sea stars, sea urchins, shrimp, snails, sponges, surf grass, tube worms, and whelks.

These creatures can grow to larger sizes because there is more available energy and better water coverage: The water is shallow enough to allow more light for photosynthetic activity, and the salinity is at almost normal levels. This area is still protected from large predators because of the wave action and relatively shallow water.

Tide pool fauna

Sea anemone, Anthopleura elegantissima clone to reproduce. The process is called longitudinal fission, in which the animal splits in two parts along its length.Sea anemones, Anthopleura sola often fight for territory. The white tentacles (acrorhagi) are for fighting. The acrorhagi contain stinging cells. The sea anemones sting each other repeatedly until one (usually) moves.
Some species of starfish have the ability to regenerate lost arms in time. Most species must retain an intact central part of the body to be able to regenerate, but a few can regrow from a single ray.The regeneration of these stars is possible because the vital organs are in the arms.

Tide pool flora

Sea palms look very much as palm trees do. They live in the middle to upper intertidal zones in areas with greater wave action. High wave action may increase nutrient availability and moves the blades of the thallus, allowing more sunlight to reach the organism so that it can photosynthesize. In addition, the constant wave action removes competitors, such as the mussel species Mytilus californianus.

Recent studies have shown that Postelsia grows in greater numbers when such competition exists — a control group with no competition produced fewer offspring than an experimental group with mussels; from this it is thought that the mussels provide protection for the developing gametophytes. Alternatively, the mussels may prevent the growth of competing algae such as Corallina or Halosaccion, allowing Postelsia to grow freely after wave action removes the mussels.

British Isles rockpool life