Caused by gravitational attraction of sun and moon and centrifugal force generated by the rotation of the earth-moon system around the sun


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Caused by gravitational attraction of sun and moon and centrifugal force generated by the rotation of the earth-moon system around the sun

  • Caused by gravitational attraction of sun and moon and centrifugal force generated by the rotation of the earth-moon system around the sun

  • Periodicity of 24 hours, 50 minutes



gravitational attraction: sun and moon pull at the Earth’s oceans, causing a tidal bulge

  • gravitational attraction: sun and moon pull at the Earth’s oceans, causing a tidal bulge

  • the tidal influence of the Moon is about twice that of the Sun



Two classifications of tide based on the orientation of the Sun and Moon.

  • Two classifications of tide based on the orientation of the Sun and Moon.

  • Spring tide : Sun, Moon and Earth are all in a line (full or new moon), Sun and Moon act together to create one large tidal bulge, and causes the greatest tidal differences because the.

  • Neap tide: Sun and Moon are at right angles from each other (quarter moon phase), when the, smaller tidal bulge.

  • distance of Moon: 50K km difference. perigee (nearest), the gravitational pull is ~40% greater than at apogee (farthest).







Approximately two high tides and two low tides each day

  • Approximately two high tides and two low tides each day

  • when it is high tide at one coastal location, it is low tide along a different coast a quarter of the way around the Earth.

  • Bay of Fundy, eastern Minas Basin, on the - Moon near perigee @ spring tide, HT up to 16 meters above LT.

  • The geogr. location, shape of the shoreline, water depth key reasons for tidal variations.





Exposure in the air for periods every day

  • Exposure in the air for periods every day

    • Greater temperature differences
    • Desiccation/water loss – time of exposure changes as tide advances
    • Intense solar radiation


Mechanical effect

  • Mechanical effect

  • Creates a “splash zone”

  • Mixing – chemicals, dissolved gases, suspended particles



Rainfall, freshwater runoff

  • Rainfall, freshwater runoff

  • Tidal pools – evaporation exceeds precipitation











































Minimize water loss/desiccation during exposure

  • Minimize water loss/desiccation during exposure

    • Hide out in most crack, crevice, under algae
    • Tolerate tissue desiccation, rehydrate at high tide
    • Structural behavioral modifications – close up, clamp down, mucus, gills in cavity


Minimize thermal stress

  • Minimize thermal stress

    • Large size, surface/volume ratio
    • Light/heat reflection
    • Evaporative cooling


3. Avoid destruction in waves

  • 3. Avoid destruction in waves

    • Attach to substrate
    • Thicker shells
    • Clamp to substrate
  • 4. Salinity stress





Supralittoral – splash zone

  • Supralittoral – splash zone

    • Littorina (periwinkle), encrusting lichens and algae
  • Midlittoral – barnacle and mussels zone

  • Infralittoral – algae and more diverse mix of animals

  • Sublittoral – subtidal zone



Period of submergence – “critical tidal level” (Doty 1945)

  • Period of submergence – “critical tidal level” (Doty 1945)

  • Desiccation – sets upper limits to organisms

    • north vs south-facing slopes
    • irregularities
  • Thermal stress

  • Sunlight



Coast of Scotland:

  • Coast of Scotland:

  • Chthamalus stellatus

  • Balanus balanoides

  • Thais lapillus (now Nucella)





Observed structure of the food web in rocky intertidal from Washington to Costa Rica

  • Observed structure of the food web in rocky intertidal from Washington to Costa Rica

  • Washington – predatory starfish Pisaster and Nucella, the drill – lots of diversity

  • Costa Rica – no starfish, the drill Nucella is the top predator – less species diversity

  • What was going on??

  • Went back to Washington and experimented



Removed starfish from rocks and observed results

  • Removed starfish from rocks and observed results

  • With Pisaster ~ 15 species

  • Without ~ 8 species (plots dominated by Mytilus, the best competitor for space)

  • Pisaster - “Keystone species” – indirectly controls the structure of whole community



Balanus glandula (like Chthamalus)

  • Balanus glandula (like Chthamalus)

  • Balanus cariosus

  • Refuge in space (Balanus glandula)

  • Refuge in size (Balanus cariosus)





Space is key – processes involved in getting, keeping, and using space

  • Space is key – processes involved in getting, keeping, and using space

  • Physical stress – desiccation, etc.

  • Physical disturbance – waves, drift logs

  • Predation – biological disturbance

  • Competition

  • Natural death



Fucus – whip effect on barnacles vs protection from desiccation

  • Fucus – whip effect on barnacles vs protection from desiccation

    • Treatment = removal of Fucus
  • Limpets – eat algae; disturb and/or eat barnacles

    • Treatment = “dog dishes” to exclude limpets
  • Thais – drills mussels and barnacles

    • Treatment = cages to exclude
  • Pisaster – eats mussels and barnacles, etc.

    • Treatment = removal


Sessile marine organisms compete for space

  • Sessile marine organisms compete for space

  • Three levels of “biological disturbance”

    • Grazing by limpets
    • Predation by Thais/Nucella
    • Predation by Pisaster
  • Pattern in nature = mosaic of disturbance and recovery; disturbance maintains patchiness, keeps diversity high



Shift in thinking about how communities are organized

  • Shift in thinking about how communities are organized

  • Earlier view – competitive dominant has broadest niche, diversity the result of specialization to avoid competition

  • New view – dominants often less abundant, inferior competitors can have broader niche, predators and disturbance create diversity by preventing competition



Upper limits of distribution are primarily determined by physical factors

  • Upper limits of distribution are primarily determined by physical factors

  • Lower limits of distribution are primarily determined by biological interactions (competition for space and predation)

  • Predation or physical disturbance can prevent competitive exclusion (enhancing species diversity) by keeping superior competitors at low densities

  • In benign physical environments, predation is most important in determining community composition

  • In harsh physical environments, predation intensity is reduced and competition is most important in determining community composition



Upper limits of distribution are primarily determined by physical factors

  • Upper limits of distribution are primarily determined by physical factors

  • Lower limits of distribution are primarily determined by biological factors (competition for space and predation)

    • Starvation restricts upper reaches
    • Larval settlement determines the limits of distribution
      • -- shorter period of inundation means reduced probability of settlement in upper reaches
      • -- larvae chose where they settle
      • -- adult larval interactions affect settlement patterns


4. In benign physical environments, predation is most important in determining community composition

  • 4. In benign physical environments, predation is most important in determining community composition

  • In harsh physical environments, predation intensity is reduced and competition is most important in determining community composition

    • Assumes prey have a greater physical tolerance than predator, can find refuges in space
    • Variations in recruitment determine the level of competition
    • Importance of predator selectivity and competitive hierarchy
    • In same environment, both predation and competition are important, both for different life stages



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