Tide pool
Shallow intertidal pools formed at low tide.
A tide pool, also known as a rock pool, is a shallow pool of seawater that forms on the rocky intertidal shore, typically ranging from a few inches to a few feet deep and a few feet across. These pools exist as separate bodies of water only at low tide, when seawater becomes trapped as the tide recedes. Tide pools are notable for hosting adaptable marine life and have engaged naturalists, marine biologists, and philosophical essayists, with theories suggesting they may have been an environment where life on Earth originated.
Quick Facts
- Tidal cycle length
- about 25 hours
- Tidal cycle composition
- two high tides and two low tides
- Depth range
- a few inches to a few feet
- Width range
- a few feet across
Facts from the source article.
Zones
Tide pools exist in the intertidal zone, the area within the tidal range that is submerged by the sea at high tides and during storms. The rocky shoreline exhibits distinct zones created by tidal movements: the supralittoral or splash zone above the high-tide mark, which is virtually terrestrial and only occasionally splashed; the intertidal fringe around the high-tide mark; the intertidal or littoral zone between high and low tide marks, further divided into high, mid, and low intertidal zones; and the sublittoral or subtidal zone below the low-tide mark. The presence and abundance of flora and fauna vary between these zones due to niche adaptations to varying tides and solar exposure. At other times, rocks may undergo extreme conditions such as baking in the sun or exposure to cold winds, and few organisms can survive such harsh conditions. The high tide zone is flooded during each high tide, occurring once or twice daily, and organisms must survive wave action, currents, and long exposure to sun and open air. This zone is predominantly inhabited by seaweed and invertebrates such as sea anemones, starfish, chitons, crabs, green algae, and mussels, with marine algae providing shelter for nudibranchs and hermit crabs. The same waves and currents that make life difficult bring food to filter feeders and other intertidal organisms. The zone constantly covered and uncovered by water has more plants and animals than the high tide zone because they are not exposed to drying conditions for so long; during low tide, anemones close up and can cover themselves in shells, and mussels close their shells to keep in moisture, reopening when the tide returns with food.
Marine life
Tide pools provide a home for many organisms such as sea stars, mussels, and clams, whose inhabitants deal with a frequently changing environment of fluctuations in water temperature, salinity, and oxygen content. Hazards include waves, strong currents, exposure to midday sun, and predators: waves can dislodge mussels and draw them out to sea, gulls pick up and drop sea urchins to break them open, sea stars prey on mussels and are eaten by gulls themselves, and black bears are known to sometimes feast on intertidal creatures at low tide. Although tide pool organisms must avoid being washed away, drying up, or being eaten, they depend on the tide pool's constant changes for food, and tide pools contain complex food webs that can vary based on climate. The sea anemone Anthopleura elegantissima reproduces clones of itself through longitudinal fission, splitting into two parts along its length, while Anthopleura sola often engages in territorial fights using white tentacles (acrorhagi) containing stinging cells, stinging each other repeatedly until one moves. Some species of sea stars can regenerate lost arms, though most must retain an intact central part of the body to regenerate, but a few can regrow from a single ray because vital organs are in the arms. Sea urchins move around tide pools with tube-like feet, and different species have different colors; their spines protect them from predators, allowing them to feed almost undisturbed, though spines of some species such as Toxopneustes pileolus are toxic and can deliver an extremely painful sting. Algae and other microorganisms attract urchins to tide pools. The presence of the California mussel increases the supply of inorganic nitrogen and phosphorus in coastal marine tide pools, making the ecosystem more productive; its shell is primarily composed of aragonite and calcite, both polymorphs of calcium carbonate, and climate change and ocean acidification have led to a decrease in these compounds in California mussel shells over many years.
More in Coastal Landforms
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced