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Low Rock/Boulder Shoreline

  Gowlland Point, South Pender Island

  Southlands Drive Area, South Pender Island

 Gowlland Pt 5 (2)  Low Rock Boulder .2.South Lands Dr SPIsland


Low rock/boulder shore types are a mix of hard bedrock ramps and boulder beaches that have a slope of less than 20%.  These low-slope, mixed rock and boulder shores are a common shore type on the Gulf Islands.

The low rock/ boulder shore type is almost 51% of the total shoreline in the Islands Trust area based on the twelve major islands that had shoreline mapping completed.  Mayne Island has the most at 66%, while Gambier Island has the least at 31%.   59% of South Pender Island's shoreline has been mapped as the low rock/ boulder shore type.

Physical Features

The low rock/boulder shores are a mixture of sediment and rock, and are moderately resistant to erosion. They tend to have a limited sediment supply and be stable over a human time scale. Sediment transport processes depend on the wave energy at the site, with more exposed shores having some onshore/offshore and longshore transport. Low rock/boulder shores often have driftwood accumulations in high intertidal and backshore areas.

Biological Features

The biodiversity at low rock/boulder shore types depends on the wave exposure and sediment mobility. Higher energy sites will have bare, mobile boulders and attached biota on rock platforms. Moderate energy shores that are more stable can have lush attached communities, including many invertebrate species which live in microhabitats under boulders.  

Like sea cliffs, the common upper intertidal zone community includes barnacles, rockweed and blue mussels on stable substrates. Diversity in the lower intertidal zone depends on wave exposures, with moderate or high exposures usually having more species than protected shores. Common species include benthic kelps, several species of red algae, and numerous invertebrates such as sea stars, crabs, anemones and others. Bull kelp often is found on immobile substrates.  

Backshore and riparian vegetation can be a major contributor to slope stability along the high water line, where established root mats help to reduce soil erosion.  

Shallow nearshore areas of these shallow sloped rock/boulder shores are important foraging areas for overwinter sea ducks and other waterfowl. 

Low Rock And Boulder Cobble WEB 

Page last updated: 01/10/15
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