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
1. What is the intertidal or littoral zone?
2. Which organisms in the intertidal zone experience the greatest changes in
abiotic factors? Why?
3. What causes the zonation within the littoral zone?
4. What is a tide pool?
5. 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
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
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 algee 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
Text is from “Rocky Shores” William A. Andrews and Sanda J. McEwan, 1987