3.4 Biological Resources
geology of the region. The mainland shelf, which extends from shore to approximately -650 feet MLLW,
comprises six percent of the 40,000-square mile Bight. There are no sensitive or endangered infauna
species in the Bight. There are also smaller Sub-bights and the project is within the Sub-bights of
Oceanside, Mission Beach, and Imperial Beach (also littoral cells).
The primary habitat of the offshore borrow sites is marine open water. Sandy substrates characterize the
bottom in the vicinity of the borrow sites; however, hard substrate may support sensitive indicator species
such as sea fans, feather boa kelp, and/or giant kelp. Sand and hard substrate bottoms characterize
nearshore and intertidal habitats within, and adjacent to, the receiver sites.
The following text provides an overview of the soft bottom and hard bottom communities which generally
occur in or adjacent to proposed borrow or receiver sites. This is followed by an overview of the mammals
(marine and terrestrial), and bird species which occur throughout the project area. A detailed description
of each individual receiver site and borrow site, in terms of both resources within the footprint and nearby,
is provided in Section 3.4.3.
Soft Bottom Communities
The benthos is a general term referring to those organisms that live in (infauna), on (epibenthic), or near
(demersal) the seafloor. Benthic habitats along the mainland shelf of the Bight can be divided into soft and
hard bottom substrates. Each harbors a distinct and characteristic community, which varies with many
environmental variables but especially water depth and substrate type. The descriptions are organized
generally from the intertidal zone seaward.
Benthic Invertebrates
The soft-bottom substrates of the mainland shelf include over 5,000 species of invertebrates. Biological
diversity is generally related to the complexity of habitats, water depth, sediment grain size, nutrients,
contaminants, shelf width, and distance from shoreline. Benthic communities can be affected by seasonal
change and episodic winter storms (waves and rain) which physically disrupt bottom communities.
Soft bottom infaunal communities have similar characteristics for a given water depth, sediment type, and
wave energy. Thus, sandy infaunal communities off of Oceanside are similar to those found at similar
depths and bottom type off of Imperial Beach. The infaunal zone is classified into general regions, including
Regional Beach Sand Project EIR/EA
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