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 air
 Can lose oxygen as it heats in the sun and
increases in salinity
 Salinity can decrease as heavy rains dilute
seawater
 Organisms: algae, sea stars, anemones, tube
worms, hermit crabs, and molluscs
 Most are filter feeders
 Infralittoral
Fringe
 Extends from the lowest of low tides to the
upper limit reached by large kelps
 Subtidal zone
 Region 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 topdown 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