Quantcast IMPACTS OF BEACON SOUTH CENTRAL COAST BEACH ENHANCEMENT PROGRAM

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organisms of direct burial by beach placement of sand is considered to be adverse but
insignificant.  On some beaches sand may be placed on cobble.  Cobble beaches
support very little marine life because the frequent movement of cobbles by the waves
results in the abrasion and scour of rocks. Again, the impacts of sand placement would
be insignificant.
Some of the sand placed on the beach will be washed into the ocean. The proposed
project also may re-nourish some beaches by pushing sand directly into the water
below the mean high tide line. Sediments resuspended by waves will settle in shallow
subtidal areas or be moved to downcoast beaches. The impacts of this secondary
burial on soft bottom organisms would be insignificant.  Soft bottom organisms in
shallow subtidal areas are adapted to the natural movement of sediments. Most would
survive the input of sand from the proposed project. If a particularly large volume of
sand settled rapidly, some organisms within a localized areas might not be able to
withstand the rapid burial. However, the area would be recolonized rapidly from the
surrounding area.
The secondary burial of organisms on subtidal reefs or in rocky intertidal habitats is of
greater concern. Natural sand movement is characteristic of the nearshore environment
in the project area. Intertidal and shallow subtidal communities, thus, are adapted to
seasonal sand movement.  The dominant macrophytes and invertebrates in these
communities are species that can withstand some sand abrasion and burial. Once they
have become established, kelp plants may withstand partial burial of their holdfasts.
Similarly, surfgrass may survive burial of their rhizomes and part of their blades. It is
not uncommon to observe kelp or surfgrass growing out of the sand. However, sand
burial could interfere with recruitment by burying juvenile plants.
Invertebrates found on low rocks within the active littoral zone shallower than about
20 ft. water depth typically are species that can withstand sand movement. Species on
higher relief or at deeper depths, however, may be more susceptible to the impacts of
sedimentation.  For example, several species of invertebrates, including stalked
tunicates (Styela montereyensis), and gorgonians (Muricea californica and M. fruticosa),
in kelp beds off San Diego County were observed to suffer mortality related to sediment
movement that either buried organisms, scoured them, or detached them from the
substrate (Rosenthal et al 1974). If large amounts of sediment are deposited in a hard
bottom area, the rocks may be buried and the habitat lost temporarily.  Natural
processes would be expected to move the sand out of the habitat and rocks would
eventually be uncovered. Recolonization of hard bottom communities has been found
to take between 1 and 10 years (Vesco and Gillard 1980, Foster et al. 1991). Recovery
of communities on low rocks in the shallow subtidal, where sand movement is frequent,
would probably be at the lower end of the observed range.  Because hard bottom
habitats are considered significant habitats, impacts of secondary burial have the
potential to be significant. The determination of significance depends on the depth of
burial, the amount of habitat affected and the length of time sand would remain at a
particular site. In general, the deposition of a foot or less of sand within a small portion
of a rocky habitat for a few months would not be considered significant, because this
level of sand burial is typical of natural sand movement in the project area.
32
3208 Bio Report
06/12/02



 


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