Intertidal Communities 1

Intertidal Communities

Rocky Shore CommunitiesSandy Bottom Communities

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The Intertidal (Littoral Zone)

The littoral 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

Spring tides Neap tides 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

Ft. Fisher is one of the only naturally occurring rocky outcrops in the S.E. U.S.

Epifauna Sessile

Living on the rocks animals are exposed to the environment which can be very stressful Animals exposed to air must have adaptations to

avoid desiccation

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Abiotic Factors (Physical) Desiccation (water loss) Extreme changes in temperature Changes in salinity Turbulence

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Water Loss (Desiccation) For survival the

duration of exposure to air is critical

Sessile animals have structural adaptations

Mussel Bed

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Dessication Algae - can

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

Littorina (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 cementing (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 Mobile animals are usually

holed up during low tide so they are not feeding

Not being able to feed at will has effects on growth rate especially those who are higher in the intertidal

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

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

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Rocky Shore Zonation

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.

Keystone species: a single species, which has a controlling effect on the community in which it lives

Keystone Predators

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Tide pools Animals have the

same physical factors to contend with

Closed Tide Pools

Open Tide pools

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Sandy Shoreline Community

Soft bottom communities are found in areas where sediment has accumulated

Dominate the east coast of the U.S and the gulf coast

Due to the environmental conditions most animals bury themselves in the substrate.

Ghost crab

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Environmental Conditions Wave action is the most important physical

factor and correlates directly with beach slope and grain size

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Sandy Beach Intertidal The swash zone is the area where most

animals are found and is the area of constant change

Some species burrow deep and extend siphons to the surface

Most animals have heavy shells and are extremely fast burrowers

Sandy Beach Zonation

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Fauna Composition Noticeably absent

are the plants, due to lack of stable substrate

Crustaceans, bivalves, and polychetes dominate sandy beaches

Predators? Feeding strategies?

Coquina clams

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Mole Crabs

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Locomotion Bivalves use a

muscular foot for locomotion

Mole crabs and other arthropods use appendages for burrowing

Sea cucumbers and worms both feed and burrow at the same time

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Meiofauna