Rocky Shorelines
What are rocky shorelines?
Rocky shorelines are composed of solid bedrock with very little sediment. They are often exposed to tremendous forces of waves and currents. Due to their bedrock composition, they are not prone to erosion in human time scales. Rather, change on rocky shorelines occurs in geologic time, over thousands or millions of years. Rocky shorelines provide habitat to many marine organisms that have adapted to life in this harsh environment.
Rocky shoreline with harbour seals: Inskip Islands in Esquimalt Harbour
Where are rocky shorelines found in the CRD harbours?
Rocky shorelines are found in many areas in Esquimalt Harbour and in small areas of Victoria Harbour, such as West Bay, McLoughlin Point, Saxe Point and Harrison Island. Other well-known rocky shorelines in the Victoria area include Cattle Point, Clover Point and Ten Mile Point.
How are rocky shorelines formed/shaped?
The bedrock composing rocky shorelines was formed millions of years ago by geologic processes (see Geologic History of Vancouver Island). Glaciers played a large role in sculpting this rock to its present form. They formed fiords and U-shaped valleys, scoured away sediment from some locations and deposited it in others. Evidence of the most recent glaciation (~29,000 to 10,000 years ago) can be seen in the features of much of the exposed bedrock around Victoria. Look for striations (parallel ridges up to a few cm in height), grooves and rounded forms. Most ridges and grooves around Victoria are oriented northwest-to-southeast, in line with the direction the glaciers flowed.
What lives on rocky shorelines?
The plants and animals that live on rocky shorelines have adapted to very challenging conditions. A basic requirement is the ability to hang on tightly, against the constant forces of waves and currents. For example, seaweeds such as kelp hold on with root-like holdfasts, barnacles secrete “cement” and mussels anchor themselves with sticky threads. Plants and animals must be able to survive large temperature changes as well as dry conditions during the low tide. Some shelled animals can capture a small amount of water and seal it in their shells. Tidepools are unique features of the rocky shoreline. These small pools of trapped seawater can contain creatures that normally occur in the subtidal zone.
Despite the hardships of this environment, abundant nutrients are provided by cool waters and constant flushing. Plant and animal communities establish in the tidal zone to which they are best suited. This results in zones called bio-bands that can be seen clearly by the type and colour of vegetation and animal life. Some of the organisms that inhabit the various bio-bands of rocky shorelines include:
- In the backshore zone (above the high tide line): lichens, insects, salt-resistant grasses and other salt-resistant land plants
- In the upper intertidal zone: lichens, barnacles, periwinkles, limpets
- In the mid intertidal zone: chitons, mussels, rockweed, whelks, purple laver (a red algae)
- In the lower intertidal zone: red algae, sea stars, Black Oystercatchers, mussels, oysters, sea lettuce, hermit crabs, shore crabs
- In the subtidal zone (below low tide line): turkish towel (red algae), kelp, surf grass, nudibranchs, sea urchins, anemones, Pigeon Guillemots, crabs, sponges, sea cucumbers, Cormorants, Greenling (fish), sculpins, rockfish, sea otters, harbour seals.
(Click on image above for illustration of intertidal zonation)
Why are rocky shorelines important?
Protection from Storm Waves
Rocky shorelines form headlands that shelter leeward shores and provide a natural breakwater.
Habitat for Plants & Animals
As described above, many species make their homes in the nutrient-rich waters of rocky shorelines.
Education, Tourism & Recreation
With so many species crowded in to a fairly accessible environment, rocky shorelines provide ideal sites for marine biology education. The beauty of these ecosystems attracts tourists and recreational users alike.
What threatens rocky shorelines?
Rocky shorelines are not very prone to erosion, so they are not as vulnerable to development as shorelines formed of soft sediment. However, the living organisms can be damaged by trampling, harvesting or pollution. Some types of seaweeds are sensitive to shading from structures such as docks, wharves and walkways.
How can I help protect rocky shorelines?
For information on protecting shorelines please visit our How Can I Help section.
Additional Information & Links
- Life on the Rocky Shore
- Discover the Seashore: Pacific Rim National Park
- Habitat: Marine Ecology and Related Issues: Virtual Museum Canada; Seaside Live
- Marine Topics and Habitats: Nova Scotia Museum
- Exploring the Intertidal: Bamfield Marine Sciences Centre
- Stewardship Centre for BC
- Yorath, C.J. and H.W. Nasmith. 2001. The Geology of Southern Vancouver Island; a field guide.