Water loss

• Major hazard at low tide is desiccation
• Some organisms hide

1. Crabs in crevices & under rocks
2. Numerous organisms in tidepools

• Some clam up or clamp down
• A few withstand desiccation (chitons, Fucus)

Temperature

• Most intertidal organisms
• Some reduce heat absorption by being light colored
• Others reduce temperature by staying in shade or water

Salinity

• Affected by rainfall and/or evaporation
• Many intertidal organisms can withstand wide salinity ranges
• Others clam up or clamp down

Effects on Feeding

• Deposit feeders are rare
• Filter feeders most common
• Grazers, predators & scavengers also present
• The higher an organism is in the intertidal the less time it has to feed

Wave Action

• Wave shock can be very strong
• Wave shock intensity varies depending on contour of shore
• Waves are refracted to be + parallel to shore

Coping with Wave Shock

• Permanent anchoring
• Clinging by suction or claws
• Hiding in sheltered locations
• Thick shells and/or low profile
• Streamlined shape and/or flexibility
• Wave action often determines community composition

Competition for Space

• First comers at an advantage so dispersal ability a must
• Epifauna and flora abundant
• Displacing or growing over competitors also occurs
• Blue mussel (sheltered) and California mussel (open)

Vertical Zonation

Factors Determining Zonation

• Zones determined primarily by tide levels
• Zones are best seen on a uniform sloping beach
• Abiotic factors determine community structure in upper intertidal
• Biotic factors determine community structure in lower intertidal

Zonation along Pacific Coast: See Handout.

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