What is the major cause of tides? And why are there usually two high tides and two low tides each day? Role of moon and centrifugal force: See Fig (Role of sun: next slide) Role of the earth’s rotation 

Effect of the sun Spring tides: sun and moon aligned Spring tides: sun and moon aligned Neap tides: sun and moon at right angles Neap tides: sun and moon at right angles

The tilt of the earth This causes the two high tides and two low tides each day to be of unequal height This causes the two high tides and two low tides each day to be of unequal height

The Oregon coast has mixed, semi- diurnal tides, as show here:

Why don’t the tides occur at the same time each day?

Tidal zones  Upper intertidal  Middle intertidal 1  Lower intertidal

Upper intertidal: submerged only on high-high, spring tides.  Upper intertidal

Middle intertidal (upper zone): exposed to air more than water, but submerged at least 1x per day  Middle intertidal (higher)

Mid-intertidal: Usually submerged 2x per day, exposed 2x per day (generally submerged a bit more than exposed)  Middle intertidal: lower

Low intertidal: Submerged except during low-low, spring tides.  Lower intertidal

Physical factors affecting distribution of organisms Extent of tidal exposure Extent of tidal exposure Amount of wave action Amount of wave action Exposure to direct sunlight Exposure to direct sunlight Temperature Temperature Substrate Substrate Other characteristics of water (see previous lecture) Other characteristics of water (see previous lecture)

Adaptations to the physical environment Trapping water within Trapping water within Limpets and others: clamping down Limpets and others: clamping down Barnacles and snails: Trap doors Barnacles and snails: Trap doors Called an “operculum” in snails Called an “operculum” in snails Anemones and snails: closing up Anemones and snails: closing up Algae: mucopolysaccharides Algae: mucopolysaccharides

Adaptations to the physical environment (cont.) Microhabitat refuges Microhabitat refuges Physiological adaptations Physiological adaptations