Tide pools are rocky pools by oceans that are filled with seawater. Many of these pools exist as separate entities only at low tide.
Tidal pools exist in the intertidal zones. These zones 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.
The intertidal zone is periodically exposed to sun and wind, so it desiccates barnacles which need to 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.
Source: en.wikipedia.org/wiki/Tide_pool - 15.03.2012