Tides and Tidal Zones

Tides

• The rising and falling of the sea
• Produced by the gravitational pull of the moon and the sun
• There are two high tides and two low tides per day

• High Tide

• Water at its highest level
• The water on the same side of the moon bulges out toward the moon
• The ocean also bulges out on the opposite side of the Earth.

• Low Tide

• Water is at its lowest level
• Moon forms a right angle with location on Earth
• The ocean is also at low tide on the opposite side of the Earth

• Spring Tide

• When the high tide and low tide have the greatest difference
• Happens during new moon and full moon
• Has NOTHING to do with Spring; called this because the tide is "springing forth"

• Neap Tide

• When high tide and low tide have the least difference
• Moderate tides
• Happens during the first and third quarter moon, seven days after spring tide

Intertidal Zones

• The shoreline is broken down into 4 tidal ‘zones’ based on beach location and how often they are covered by water.
• Upper intertidal

• Location of extreme high tide waters
• Positive tide

• Middle intertidal

• Location of normal high tide waters
• Positive tide

• Lower intertidal

• Location of normal low tide waters
• Negative tide

• Not an intertidal zone, but…

• Subtidal

• Location of extreme low tide waters
• Negative tide

Adaptation

• A characteristic that helps a living thing survive and function better in its environment.
• Organisms that live in the intertidal zone have different adaptations that allow them to survive.

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Unique conditions of intertidal zones

Sometimes area is dry

• Necessary adaptations

• Must be able to tolerate exposure to air
• Organisms must have a way to prevent drying out
• Example: Shells of oysters or snails

Intense wave action

• Organisms must be able to tolerate splashing
• Necessary adaptations

• Thick shells (Turban snails)
• Ability to attach to rocks (Barnacles and Anamones)
• Barnacles open and close to hold in water to keep from drying out
• Anemones survive wave action by attaching themselves to the side of large rocks

• Splash zone

• Area high on beach
• Dry most of the time
• Only wet when wave splashes
• Species adaptation:

• Must be able to prevent drying out. Many have protective shell
• Example organisms: Lichen, isopod, periwinkle snails, amphipods

• Upper Intertidal Zone

• Only covered by water at high tide
• Intense wave action
• Special species adaptation:

• Thicker shells, attach to rocks
• Example Species: Anemones, barnacles, turban snails

• Middle Intertidal Zone

• Most active region
• Covered and uncovered by water twice a day
• Special Adaptation:

• Must be able to tolerate submersion in water AND exposure to air
• Example species: seaweed, crabs, sea stars, mussels

• Low Intertidal Zone (and Subtidal Zone)

• Usually submerged
• Most food and shelter
• High diversity of organisms
• Animals are NOT adapted to exposure to air.
• Special adaptation:

• Creatures are mobile
• Example organisms: Predators: fish, octopus, and jellyfish

• Threats to Intertidal Zones

• Limited time to feed
• Changing temperatures
• Changing salinities
• People