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)
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