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Intertidal Communities

Rocky Shore Communities

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The Intertidal The intertidal zone

is the area between the highest high and the lowest low tide

Organisms that live in this area undergo the greatest variations in environmental conditions

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Tidal Forces Gravitational pull on the earth by

the sun and moon combined with centrifugal force generated by the earth-moon-system

Semidiurnal tides Diurnal tides

Spring and Neap Tides

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Rocky Intertidal Community

Rocky coasts usually occur on steep coasts that lack sediment

Fort Fisher is one of the only naturally occurring rocky outcrops in the S.E. U.S. Epifauna Sessile

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Abiotic Factors

Desiccation Extreme changes in temperature Changes in salinity Turbulence

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Water Loss For survival the

duration of exposure to air is critical

Sessile animals have structural adaptations

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Dessication Algae - can

withstand 70 - 90% of water loss in tissues and survive

Littorina sp. (Periwinkle) reduce area in contact with the substrate and have a light colored shell to deal with extreme heats

Algae mat at low tide

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Changes in Temperature Due to its high heat capacity water shows a

minimum change in temperature when compared with the air

If extreme temperature does not kill an organism it may severely weaken it and cause it to die of secondary causes

Extreme temperatures may hasten desiccation

Adaptations

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Drastic Fluctuations in Salinity

Salinity may change due to severe rainfall If severe enough at

low tide the entire community may experience high mortality

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Wave Action

Waves act to smash and tear organisms from the substrate

Sessile animals use cement (barnacles), holdfasts (seaweeds) and, byssal threads (mussels)

Mobile animals have appendages for clinging and snails have an enlarged foot used for attachment

Wave action also effects the intertidal by disturbing the substrate

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Modes of Feeding Due to the lack of

sediment there are no deposit feeders!

Almost all of the sessile animals are filter or suspension feeders

Heavy wave action also effects feeding

Suspension

Feeding

Barnacles

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Vertical Zonation Species settle in specific vertical bands

based on their ability to withstand exposure to air

The rocky intertidal provides many microhabitats (Numerous niches)

High species diversity Distinct banding which progress from the low tide

line to the high tide line Zonation occurs due to a both physical and

biological interactions

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Rocky Shore Zonation

Organisms are found in a given area by their ability to compete and deal with physical factors. Most animals in the intertidal live near the upper end of their lethal limitsLower distribution is determined by competition and predation

Supralittoral zone

Midlittoral zone

Infralittoral

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Biotic Factors Competition

Due to the limited amount of area, competition for space is acute

Succession – natural progression of communities The creation of open spaces results in quick

colonization by opportunistic species. Soon replaced by slower growing competitively

dominant spp.

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Keystone Predators Keystone species: a single species,

which has a controlling effect on the community in which it lives

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Tide pools

Animals have the same physical factors to contend with

Closed Tide Pools

Open Tide pools