tidal pool

Tide pool with sea stars, sea anemone and sea sponges in Santa Cruz.

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."^[1]

The life in tide pools

Sea star, Pisaster ochraceus consuming a mussel in California 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 few hazards that tide pools animals should endure to survive.

Waves can dislodge mussels and draw them out to sea. Gulls pick up and drop sea urchins to break them open. Starfishs prey on mussels and are eaten by gulls themselves. Even large predators as black bears sometimes feast on tide pool creatures at low tide.^[2] Although tide pool organisms must struggle to 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.^[1]

Tide pool zones, from shallow to deep

A large sea anemone Anthopleura sola is in the process of consuming a "by-the-wind-sailor" Velella velella a blue jellyfish

Spray/splash zone

This zone gets spray during high tides and water during storms. At other times the rocks bake in the sun or are exposed to cold winds. Only few organisms can survive such harsh conditions. Lichens and barnacles live in this region.^[1] In this zone, different species of barnacle live in very tightly constrained locations, allowing the exact height of an assemblage above or below sea level to be precisely determined.

Since the intertidal zone periodically desiccates, barnacles are well adapted against water loss. Their calcite shells are impermeable, and they possess two plates which they can slide across their aperture when not feeding. These plates also protect against predation.^{[verification needed]}

Postelsia palmaeformis at low tide in California tide pools

Low tide zone in a California tide pool

High and mid tide zone

The high tide zone is flooded for few hours every day during each high tide. The organisms there 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 in food to the filter feeders and other tide pool animals.

Low tide zone

This subregion is mostly submerged — it is only exposed at the point of low tide and for a longer period during extremely low tides. This area is teeming with life; the most notable difference of this subregion compared to the other three is that there is much more marine vegetation, especially seaweeds. There is also a great biodiversity. Organisms in this zone generally are not well adapted to periods of dryness and temperature extremes. Some of the organisms in the low tide zone area are 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.

Creatures in this area can grow to larger sizes because there is more available energy in the localised ecosystem and because marine vegetation can grow to much greater sizes than in the other three intertidal subregions due to the better water coverage: The water is shallow enough to allow plenty of light to reach the vegetation to allow substantial photosynthetic activity, and the salinity is at almost normal levels. This area is also protected from large predators such as large fish because of the wave action and the water still being relatively shallow.

Tide pool fauna

Sea anemones, Anthopleura sola engaged in a battle for territory

Sea anemone, Anthopleura elegantissima clone to reproduce. The process is called longitudinal fission. Few hours (or days) later after longitudinal fission has begun instead of one sea anemone there will be two.^[3] Sea anemones, Anthopleura sola are often seen to fight a war for territory. The white tentacles are fighting tentacles called acrorhagi. The acrorhagi contain stinging cells. The fighting sea anemones will continue to sting each other over and over again. After war ends one of them usually moves.^[4]

Some species of starfish have the ability to regenerate lost arms and can regrow entire new arms in time. Most species must have the central part of the body intact to be able to regenerate, but a few can grow an entire starfish from a single ray.The regeneration of these stars is possible due to the vital organs kept in their arms.^[5]

Tide pool flora

Sea palms look very much as palm trees do. They live in the middle to upper intertidal zones in very wavy areas. 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.^[6] Alternatively, it is thought that 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.^[7]

See also

• British Isles rockpool life

References

External links

Wikimedia Commons has media related to: Tide Pools

• Tidal swimming pools in Britain