Rocky Shores

Abiotic Factors and Zonation

• All ocean shores are exposed to tides• Intertidal zone or littoral zone – zone between high and

low tide marks• Conditions are always changing • When the tide is high, it is covered in water• When the tide is low, it is moist and salty

• Those that are in the upper region experience the sun and drying wind the longest time

• The littoral zone has several zones within it

• Rocky shores show the greatest variation, so they have the widest variety of habitats for algae to live and animals can feed

• Rocky shores have three main zones:

• Intertidal zone – covered and exposed by water, throughout the day

• Spray zone is above it

• Below it is the sublittoral zone or ocean ocean

• The zones are quite similar throughout the world

• Rocky shores can have steep cliffs or be flat

• May have crevices and gullies

• Waves erode rocky shores

• Tide pools are water-filled depressions that are present on rocky shores when the tide recedes

Section Review

• What is the intertidal or littoral zone?• Which organisms in the intertidal zone

experience the greatest changes in abiotic factors? Why?

• What causes the zonation within the littoral zone?

• What is a tide pool?• What are the three main zones of a rocky

shore?

Zonation

• Conditions are always changing• Exposed to sunlight, rain, wind, and

temperature changes• Tides and waves bring changes in salinity,

temperature, and light• Dessication is a loss of moisture and is a

big problem – some bury themselves, some move with the tide, and others have adapted to prevent dessication

• Six subzones:– Black zone– Barnacle zone– Rockweed zone– Irish moss zone– Blue mussel zone– Kelp zone

Black Zone

• Calothrix is often present

• Upper most of the zones• Every two weeks the

spring tides cover this zone

• Also gets wet from waves and spray

• Blue-green algae and lichens live here, and give the rocks their black colour

Calothrix

Black Zone

• Calothrix:• Consists of filaments of microscopic cells• Filaments are surrounded by sticky

gelatinous sheath• This allows it to stick to the surface,

protects it from drying out, and protects it from changing salt levels

• “fixes nitrogen” so lack of nutrients is not a problem

Black Zone

• Rough periwinkle• Main herbivore• Eats Calothrix for its

nitrogen content• Shell is thick and has

a small opening to prevent water loss

• Can seal itself to a rock with mucus if it gets too dry

Barnacle Zone

• Covered and uncovered daily by the tides

• Barnacles are crustaceans

• Live stuck to the rocks and depend on tides for food

• Barnacles open up during high tide and sweep microscopic organisms such as diatoms and dinoflagellates into it

• They close during low tide to prevent water loss

Barnacle Zone

• Limpets, dog whelks, periwinkles, and blue mussels may be found here

• Limpets scrape algae from rocks

• Dog whelks eat barnacles, mussels, and periwinkles

• Blue mussels will be small, and are filter feeders

Rockweed Zone

• Brown algae called rockweeds live here

• Usually 30-40cm long

• Bladder rockweed is very common on the east coast

• Thick cell walls to prevent water loss

• Air bladders help it float

• It sticks to a rocky surface with a holdfast

• Smooth periwinkle is a characteristic animal of this zone

• Graze on rockweeds• Move under the

rockweeds when the tide is out to retain moisture

• Limpets are found here as well, feeding on the rockweed

• (Limpets are like a snail)

Irish Moss Zone

• Chondrus crispus is a red algae (known as Irish Moss)

• With Gigartina stellata form a spongy carpet

• Zone can be purple, or green and yellow• Out of the water for a few hours a day• Not tolerant of temperature extremes or

dryness• Algae retain their water at low tide

Chondrus crispus

Irish Moss Zone

• Isopods, amphipods and decapods live here

• Irish moss contains carrageenin – which forms a gel; used in ice cream, toothpaste, chocolate milk, evaporated milk, and body lotions

Blue Mussel Zone

• May overlap the Irish moss zone

• May sometimes go up to the bottom of the barnacle zone

• Can be tightly packed

• Attach to rocks with threads made of protein

• Mytilus edulis is very common

Mytilus edulis

Blue Mussel Zone

• Underwater most of the time, or waves will be covering it

• Mussels are filter feeders – their respiration passes water over the gills, the gills filter out food particles (phytoplankton, bacteria, detritus)

• Main predators are whelks, starfish, and humans• Whelks bore through their shells and removes

the interior of the mussel• Starfish pry open the shell, and releases its

stomach through its mouth and into the mussel, then takes its stomach back

Kelp Zone

• Lowest zone• Brown algae, Laminaria• May be uncovered once every

two weeks during spring tide, but waves may keep it covered

• Kelp provides food and habitat• Limpets, mussels, isopods,

amphipods, crabs, and starfish live here

• Starfish move from kelp beds to mussel zone during high tide

Kelp Zone

• Kelp and other brown algae are collected for food

• Used to provide iodine• High protein and vitamin content• Feed for domestic animals• Ground to make fertilizer• Alginic acid is used as a stablilizer in ice

cream and some paint; and found in some antibiotics