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