Intertidal Ecology, part 1

I. Environmental Conditions
    A. Tides
        1. Review
            perigee (closer)
            apogee (farther)

              spring tides -- greatest range
              neap tides -- minimum range
           
        2. Descriptions of different tidal cycles
            a. diurnal tides -- one low and high tide per day
            b. semidiurnal tides -- 2 lows and highs per day
            c. mixed tide
        3. Critical tide levels

    B. Exposure - emersion (opposite of immersion)
       

    C. Temperature

    D. Wave action
        1. mechanical damage
        2. can move substrate
        3. extends the intertidal

        4. mixes oxygen into the water
        5. low light penetration -- bubbles and sediment resuspension
    E. Salinity
        1. may be exposed to rainwater when tide is low and can cause mass mortality
        2. tide pools can evaporate and increase salinity
    F. Ice
    G. Substratum type

II. Adaptations of Intertidal Organisms
    A. Resistance to water loss -- "run and hide or clam up"
        1. behavioral adaptations – migrate, burrow, hide in moist spot
        2. physiological adaptations to prevent water loss
            a. shells
            b. mucus
        3. withstand desiccation and can still be revived

    B. Maintenance of Heat Balance
        1. overheating in summer and freezing in winter
        2. high temperatures
            a. reduce heat gain - relatively large body size (small SA/volume)
            b. increase heat loss
                (1) sculpturing/ridges on shell -- are radiators for heat
                (2) light coloration -- reflect light
                (3) have extra water supply that they can use for evaporative cooling

            c. some have amazing tolerances
    C. Mechanical Stress
        1. gluing to the substratum
 
        2. strong shells
        3. squat bodies with streamlined shapes to avoid lift and drag
        4. algae are often large and are flexible and bend as the waves pass over
    D. Respiration
        1. gills enclosed in a protective cavity to avoid desiccation
        2. some animals have reduced gills and a ‘lung’ for respiring in air
        3. often move less and respire less at low tide when are closed up
        4. some fish have cutaneous respiration accounting for 1/2 of gas exchange
    E. Feeding
        1. feed more at high tide
        2. often don't feed at low tide
        3. often more suspension/filter feeders or scraping grazers; predators
    F. Salinity Stress
        1. clam up
        2. burrow
        3. osmoregulators
        4. osmoconformers -- no mechanisms to control salt content of bodies
    G. Reproduction
        1. many sessile species rely on planktonic larvae for dispersal
        2. breeding cycles are synchronized with tides
        3. some organisms migrate to the sea to deposit their eggs

III. Rocky Shores --
    A. Atlantic and Pacific Rocky Shores
        1. Atlantic
            a. rocky areas are mostly in north, where there are extreme temperature changes (-20 to +40 oC) -- regular destruction of intertidal organisms
            b. lower species diversity
            c. many extinctions during ice ages
            d. dominant herbivore, Littorina littorea, and dominant predator, green crab, Carcinus maenus, are introduced species
        2. Pacific
            a. dominated by rock from Alaska to California and also Hawaiian islands
            b. air temperatures less extreme
            c. higher species diversity
            d. most areas not glaciated recently or had southern refugia
            e. more chitons and limpets as common herbivores (native)
    B. Zonation – pattern of distribution and abundance of organisms
        1. size of zone depends on slope, tidal range and exposure to waves

        2. Stephenson Universal Scheme (1949) -- defined common terms to allow comparison of different areas --
                zones based on limits of certain groups of organisms
            a. supralittoral or maritime terrestrial
            b. upper -- supralittoral fringe --
                (1) seldom submerged
                (2) from upper limit of barnacles to upper limit of Littorina (periwinkle) 'periwinkle zone'
                (3) grazing snails and black encrusting lichens dominate; predators: crabs, snails, birds and terrestrial mammals
                (4) extreme high tide area and wave splash zone
            c. midlittoral zone
                (1) more often submerged -- daily covering and exposure
                (2) broadest zone -- often is subdivided
                (3) from upper limit of large kelps (e.g., Laminaria) to upper limit of barnacles
                (4) barnacles, predators of barnacles
            d. infralittoral fringe
                (1) submerged most of the time
                (2) from lowest low tide to the upper limit of the large kelps
                (3) diverse assemblage
                (4) organisms may only tolerate limited exposure
            e. infralittoral or sublittoral -- not exposed; below the intertidal zone

    C. Types of experiments
        1. Transplant experiments

        2. Removal experiments

        3. Caging experiments

        D. Causes of zonation –
            1. abiotic (often correlated with biotic factors – example, exposure and lack of feeding;
                    physiological tolerances must be tested directly)
                a. tolerances to exposure
                    wave tolerance
                      Gulf of Maine  example
         

                    

            b. desiccation
                (1) slopes that dry out slower (less sun) have same organisms higher on the slope than do adjacent sun-exposed slopes
                (2) critical tide levels
                (3) microhabitat
                (4) if researchers drip seawater, organisms extend their range upward
                (5) transplanted organisms from lower zones die
            c. temperature
                (1) synergistic with desiccation

                   Barnacle example

                (2) Algae -- Chondrus crispus is killed by freezing, but Fucus is not
            d. sunlight (UV)
        2. biotic
            a. competition
                (1) only occurs if there is a limited resource
                (2) most common limiting resource in rocky intertidal is space
                (3) In the Chthamalus/Semibalanus interaction, S. outcompetes in lower areas
                        by overgrowing, uplifting or crushing

            b. predation
                (1) keystone species --
                    (a) (Paine 1969) single predator that preferentially feeds on and controls the abundance of a dominant competitor,
                            thus allowing a more diverse community with inferior competitors to exist (preventing competitive exclusion)
                    (b) more recent definition includes non-predators that control community structure and have a large effect
                            on communities, (disproportional to their abundance)
                    (c) importance of ‘indirect effects’
                (2) diffuse predation -- overall high predation rates by several predators that controls the competitive dominant
                (3) weak predation -- total predation on competitive dominant is low
                (4) can also affect growth forms of different organisms – inducible defenses
                (5) examples
                     Mytilus and Pisaster ochraceus (original keystone species)
                      New England coast

            c. grazing -- dominant grazers: gastropods, some crustaceans, sea urchins and fishes
               
               (1) direct and indirect grazing effects
                    (a) may directly exclude/reduce a species by eating it
                    (b) may indirectly exclude a species -- e.g., may prevent algal growth that is necessary for dominant kelp to settle and survive
                (2) defenses of algae
                    (a) grow fast
                    (b) chemical defenses
                    (c) life history strategies
 
                (3) More types of grazers in the tropics (crabs and fishes are more important there)
            d. larval recruitment (settlement)
                (1) current patterns
                (2) habitat-dependent settlement by larvae
                (3) habitat-dependent survival
                (4) stochastic processes – good recruitment and/or survival in some years, poor in others

            e. top-down (predator and grazer) vs. bottom-up (nutrient and food) effects
                (1) top-down effects are well-documented
                (2) bottom-up effects less studied – long thought that food was sufficient
                (3) some recent comparisons of productive and unproductive areas in the same region suggest that bottom-up may be important, too
        3. general rule: (not universal) upper limits are set by physical factors and lower limits are set by biological factors
        4. interactions of biotic and abiotic

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