Intertidal Communities
Lies between the highest high tide and the lowest low tide
Stressful environment constant environmental changes
Characteristics of the Intertidal Zone
Experience daily fluctuations in their environment Organisms must be able to tolerate
radical changes in temperature, salinity, moisture, and waves
High tide When organisms are most
active Foraging for food, finding
mates, and reproducing Water contains food for
filter feeders and oxygen for organisms with gills
Low tide Organisms exposed to air Gilled animals must
protect respiratory structures from drying out and collapsing
Filter feeders withdraw into protective coverings
Rocky Shores Formed from lava flows or highly eroded areas where
sediments have been removed by wind and waves Rocky shore zonation:
Separation of organisms into definite horizontal bands Rocks provide a stable surface for organisms to attach and
provide a hiding place Zones were established based on limits of organism
distribution Width varies depending on the amount of exposure, slope of the
shore, and tidal conditions
Supralittoral Fringe (called splash zone) Uppermost area Covered only by the highest tides Receive very little moisture Supports only a few organisms (ex: limpets,
isopods, periwinkles) Supralittoral (maritime zone)
Above high water May extend several miles inland
Midlittoral (true intertidal) zone Below the supralittoral fringe Regularly exposed to low tides and
covered during high tides Organisms must withstand force of waves
during low tide (called wave shock) Upper zone: acorn and rock barnacles Middle and low zone: oysters, mussels,
limpets, and periwinkles Brown algae called rockweed
Tide pools Depressions in the rocks that retain water Prevent organisms within them from being
exposed to airCan lose oxygen as it heats in the sun
and increases in salinitySalinity can decrease as heavy rains
dilute seawater Organisms: algae, sea stars, anemones,
tube worms, hermit crabs, and molluscsMost are filter feeders
Infralittoral FringeExtends from the lowest of low
tides to the upper limit reached by large kelps
Subtidal zoneRegion of shore covered by water
even during low tide
Tropical Rocky Shores Supralittoral fringe divided into 3 zones
White zone: border between land and the sea
Gray zone: farthest zone from the low tide line where macroscopic marine algae grow
Black zone: immersed only at the highest spring tides
Midlittoral zone True intertidal zone Divided into 2 zones
Yellow zone: yellow or green depending on algae covering its surface
Pink zone: characterized by encrustation of coralline algae
Infralittoral fringe (surf zone) Includes edge of the lower
rocky platform and parts of the reef
Subtidal zone Relatively barren Small red algae
Intertidal Fishes True residents
Ex: clingfishes, blennies, gobies, sculpins, and rock eels
20-67% of inhabitants of tide pools Usually 8-12 inches long Scales absent, reduced, or very firmly attached Body shape compressed and elongated or depressed
Temporary inhabitants Tidal visitors (to feed),
seasonal visitors (to breed), and accidental visitors (trapped by storms)
Ecology of the Rocky Shore
Life influenced by level of primary production, recruitment (larval settling), herbivory (grazing), predation, and competition
Competition, herbivory, and predation are top-down factors Effects may flow down the food chain
Nutrient availability and recruitment are bottom-up factors Affect the base of food chains
Sandy Shores Role of waves and sediments:
Heavy wave action carries off much of the finer sediment Fine sandy beaches have very little wave action
Greater water retention Good for burrowing
Course sandy beaches Drain well Dry out quickly Support fewer organisms
Comparison to rocky shores Lack distinct pattern of zonation
Appear barren and devoid of life Sandy shore zonation:
Less defined 3 zones
Supralittoral From high tide line to where terrestrial
vegetation begins Midlittoral zone
Most inhabitants are burrowers Subtidal zone
Exposed only during lowest spring tides
Meiofauna
Microscopic organisms Inhabit spaces between sediment
particles of midlittoral and subtidal zones Entirely aquatic
Require water within spaces of sand to survive Greatest in number in beaches protected
from wave action