Intertidal zones tides and the coastline
1 / 32

Intertidal Zones, Tides and the Coastline - PowerPoint PPT Presentation

  • Uploaded on

Intertidal Zones, Tides and the Coastline. Overview:. Coastline Tidal Cycle Intertidal Zones Sand Flow Coastal Strand Community. California Coastline. 1100 miles long. With varying inland climates from warm by San Diego to Cool in Humboldt.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' Intertidal Zones, Tides and the Coastline' - zorion

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Intertidal zones tides and the coastline

Intertidal Zones, Tides and the Coastline


  • Coastline

  • Tidal Cycle

  • Intertidal Zones

  • Sand Flow

  • Coastal Strand Community

California coastline
California Coastline

  • 1100 miles long.

  • With varying inland climates from warm by San Diego to Cool in Humboldt.

  • Coast rarely freezes, or exceeds 100 °F. Temperature moderate year-round.

    • San Francisco January 51 °F average, and in September 62 °F.

    • Water is cold around 50 °F. Down South warms to about 60 °F.

    • Summer fog, fog drip.

    • Nutrient rich Upwelling off shore

Coastline geology
Coastline Geology

  • Coastal rocks are uplifted from sea floor. (Emergent Coastline)

    • North Coast Franciscan sedimentary Rocks about 100-150 MYA.

    • South 60 MYA sedimentary rocks.

  • Easily eroded, soft rocks. Cuts deep surf-cut shelves or benches.

    • With uplifting these shelves become terraces, but also erode away.

  • River mouths cut through valleys, form wide lagoons with a sand bars.

    • Form shoreline lakes dammed by sand

Tidal cycle
Tidal Cycle

  • Approximately Every “day” (24 hrs. 48 mins.) has two high tides and two low tides.

    • One high tide is higher than the other: Hi-Hi

    • One low tide is lower: Lo-Lo

  • Daily Tidal cycle:

    • Hi-Hi; Lo-Lo; Hi-Lo; Lo-Hi repeat…….

    • tides change every 6 hrs. 12 mins.

    • full cycle in 24 hrs. 48 mins. (one Lunar orbit)

    • offset by about an hour per day

Sea level
Sea level

  • Means slightly different things depending on how precise you need to know.

    • Mean Sea level- the average between hi’s and lo’s of tides over 19 years, measured in the water compared to land based points of reference

    • Surface of open ocean (used to calculate altitude for aviation) satellite

  • Also used is Mean Lower Low Water (MLLW) average lo-lo tide

Tidal sequence
Tidal Sequence

Higher-High tide


Sea level

Higher- Low tide

Lower-Low tide


  • Influence of gravitational pull from Sun and Moon. Moon’s pull is stronger because it is closer.

    • Centrifugal force also important.

  • Spring tides (Upwelling) every two weeks or so

    • Sun’s pull adds to moon’s pull

  • Neap tides (Scarce) every two weeks or so.

    • Moon’s pull partially counteracts sun’s pull.

  • Sun’s influence changes with season,

    • closer in June and December stronger tides.

  • Moon’s distance varies by 15,000 miles over a month

    • Perigee (2x month) is when moon is closest makes stronger tides

    • perigee with a spring tide increases by 40%

    • At Apogee (2x month) moon is farthest and weakens tides

  • Most extreme spring tides are at perigee in June and December !!

Spring tide

  • Spring and Neap Tides

Neap tide

Friday april 20th
Friday April 20th

  • Low tide is at 8:13 a.m.

  • Meet at Schoolhouse beach, 7:45 a.m., need to leave DVC at 6:00 a.m.

  • At Beach till 8:45

  • Dunes from 9:00- 10:00

  • Home by noon !!!

Intertidal zones from highest above to lowest in water
Intertidal Zones(from highest above to lowest in water)

  • Splash / Spray Zone wetted by surf

    • crustose lichens, sea lice

  • High Tide Zone - covered at high tide exposed most of the day

    • Limpets, sea lettuce, acorn barnacles, rockweed

  • Middle Tide Zone -exposed only for short periods

    • barnacles, mussels, sea stars, chitons, urchins

  • Low Tide Zone -exposed only at lowest tides

    • Top of lower intertidal is sea level for that area.

    • sea palm, surf grass

  • Sub-tidal Zone - never exposed

  • Highly productive

Vertical zonation
Vertical Zonation

  • Total number of hours exposed to air increase towards top of rock

  • Predation changes

  • Heat

  • Desiccation

  • Wave action

Intertidal succession
Intertidal Succession

  • Sever competition for space

  • Rocks over-turned over in storms, leave bare areas.

    • Filamentous and foliose green algae colonize bare rock

    • Crustose and Coralline algae take over

    • Acorn barnacles colonize by prying off algae as they take over

    • Gooseneck barnacles and mussels take over, growing over an preying off acorn barnacles.

    • Gooseneck barnacles and mussels remain as climax, unless predator invades or rock is over turned.

    • One-year sequence.

Keystone species
Keystone species

  • Pisaster (Sea Star) defends tide pool from being taken over by mussels, barnacles.

Sea otters maintain kelp forest
Sea Otters maintain Kelp forest

  • Otters are a Keystone species

  • Kelp are the base of the kelp forest community

  • Urchins eat kelp at their base

  • Otters eat urchins, keeping their numbers low.

  • Otter numbers along California are dropping.

  • Alaska- Orcas starting to eat otters, because seal numbers are dropping

  • No fish for seals

Competition for space on the rocks
Competition for space on the rocks

Weak competitors stuck higher up in the intertidal

Sand flow
Sand flow

  • Sand from weathered rocks up in mountains.

    • banks of Merced River in Yosemite

  • Moves out to sea - westward

  • Waves come form the NW moving sand southward and back towards shore.

  • Zig- Zag flow with seasonal cycles - beach erosion with storms.

  • In winter

    • beach (more narrow) smaller,

    • more sand moved farther off shore

  • In summer

    • Wide beaches

    • Sand pushed back on to shore, now farther south.

Erosion beach decline
Erosion & Beach decline

  • River of sand slows: damming up stream, beaches disappear

    • Bodega head pushes out into sea, traps southward sand flow forming dunes

  • Sea walls impede southward flow of sand from north.

  • Headlands erode in surf, waves wrap around and hit sides

  • Resistant rocks remain longer forming stacks and arches.

Coastal strand communities
Coastal Strand Communities

  • Dunes

  • Three zones:

    • Fore dune – the beach area

    • Crest – highest point on dunes

    • Back dune- protected areas behind front dunes

Dune plant adaptations
Dune Plant adaptations

  • prostrate growth- rhizomes

  • gray hairs on leaves deflect light, air

  • nitrogen-fixing bacteria

  • thick waxy cuticle

  • deep roots

  • mycorrhizae

Fore dune
Fore dune

  • shifting sands

  • heavy winds and sand-blasting

  • Lots of sun-light, uv radiation

  • drains quickly, dry substrate

  • Not salty! Rain, fog wash out salt spray residue (doesn’t bind to sand)

Crest and back dune
Crest and Back dune

  • Crest

    • Strongest wind

    • European beach grass

  • Back dune-

    • sheltered by crest

    • warmer

    • calm, less breeze

    • beginnings of soil (organic debris)

    • mature trees, shrubs