Ancia Road, South Pender
|Razor Point, North
Boulder/cobble shorelines are shallow sloping sediment beaches
which are moderately resistant to erosion. The beach slope and form
are determined by wave and tide action. On moderate to high wave
energies, the smaller cobble material will be mobile, while in more
sheltered areas the beach material will be stable. This shore type
is common in Baynes Sound.
The boulder/ cobble shore type is 9% of the total shoreline in
the Islands Trust area based on the twelve major islands that had
shoreline mapping completed. Denman Island has the most at
29%, while Lasqueti Island has the least at 3%. 4% of
South Pender Island's shoreline has been mapped as the boulder/
cobble shore type.
Boulder/cobble shorelines at moderate and high wave exposures
may be subject to erosion during storms, however, the finer
sediments in the mixture are more easily transported and can
accumulate in pocket beaches between more stable shore types if
longshore transport is present. Boulder/cobble shorelines may be
stable or dynamic and are likely to change on a human time
Boulder cobble beaches often occur at the base of unconsolidated
bluffs or banks as 'lag' deposit where larger materials are left on
the beach after finer sediments have washed away.
On moderate to high energy boulder/cobble beaches, the beach may
be scoured and bare of attached algae and invertebrates, with
mobile invertebrates like shore crab and sea stars living under the
boulders and cobbles. In lower wave energies in particular,
burrowing animals such as clams and various species of worms are
present in the finer sediments.
On sheltered shores and bays, upper intertidal zone communities
commonly include rockweed, barnacles and blue mussels, along with
Bull kelp may be found in areas of moderate to high wave
exposures or higher tidal currents where substrate is immobile
(i.e., boulders). Benthic kelps are also present in the lower
intertidal zone at all but the most protected exposures, and mobile
invertebrates such as sea stars and crabs may be common.
Eelgrass, a shallow water flowering plant, is often present in
protected wave exposures in pockets of finer substrates of sand or
mud or seaward of the boulder/cobble beach. A highly productive
community, eelgrass beds provide important nursery areas for many
species of fish, including herring and juvenile
Shallow nearshore water can be important feeding areas for
diving sea ducks and other waterfowl.
The coastal riparian vegetation, dune grasses and other
salt-tolerant plants adapted to the dynamic environment of the
upper intertidal zone transition between marine and terrestrial
habitats play an important role in stabilizing the upper beach as
well as contributing to productivity.