Mobile invertebrates and vertebrates that are found on rocky intertidal shores are typically divided into two categories based on the amount of time spent between tidemarks. Resident species remain in the intertidal zone throughout most of their life and face a large range of local physical conditions that they mitigate by a variety of behavioral and physiological adaptations. Many residents find shelter during low tides, either between rocks, under algae, or in tide pools, while other species attach to exposed rock surfaces just ahead of the incoming tide. Transient species are those that spend only a small part of their life cycles in the intertidal zone (e.g., as juveniles) or are those that enter and leave the intertidal zone during low or high tide.
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