appendix b final 2008 biological surveys of los angeles and long ...

8.0 Eelgrass
distribution of eelgrass within temperate estuaries can also decline (Borum 1985, Twilley et al.
1985, Orth et al. 1986).
The following analysis compares the 2000 baseline for eelgrass beds within the Ports of Los
Angeles and Long Beach (MEC 2002) to the present 2008 studies, along with a discussion of
temporal and spatial variations. The methods used for surveying and analysis of eelgrass beds
are presented below.
8.2 METHODOLOGY
Surveys conducted in 2008 to document eelgrass communities within the Ports used a variety of
established techniques including aerial photography to map bed extent, side-scan sonar to map
extent and bathymetry, and diver surveys to validate and ground-truth the aerial and side-scan
methods. Tierra Data Inc. (TDI) researchers conducted side-scan sonar surveys to determine
eelgrass presence and density (determined by method resolution) in spring and fall 2008,
followed by diver side-scan sonar verification and leaf shoot (turion) density surveys during the
same seasons. Documentation of eelgrass turion density using diver performed quadrats
served two primary purposes. First, turion density measurements within eelgrass beds provided
information on the relative consistency and continuity of the individual eelgrass beds in
conjunction with knowledge of the dominant plant characteristics (e.g., blade size) and
associated species. Secondly, diver-performed turion density counts provided important ground
truthing information for the evaluation of side-scan sonar imagery.
The methods used during 2008 baseline study eelgrass surveys were complementary to those
used during the baseline study conducted in 2000 (MEC 2002), and consistent with
methodologies specified by the Southern California Eelgrass Mitigation Plan Policy (SCEMP) for
monitoring eelgrass mitigation sites. Diver surveys to evaluate eelgrass turion densities and
ground truth side-scan sonar imagery were performed more intensively in 2008 compared to
previous baseline studies in order to access spatial consistency of identified eelgrass beds while
capturing the maximum turion densities of individual stands as reported in the 2000 baseline
surveys. The National Oceanic and Atmospheric Administration (NOAA), National Marine
Fisheries Service (NMFS), U.S. Fish and Wildlife Service (USFWS), and California Department
of Fish and Game (CDFG) developed the SCEMP to provide monitoring and remediation
guidelines for unavoidable impacts to eelgrass resources. SCEMP provisions require any
impacts to eelgrass be mitigated in a manner that compensates for direct habitat loss. SCEMP
also requires monitoring of mitigation areas and suitable local reference sites for a period of 5
years to assess mitigation site performance compared to a natural reference bed.
8.2.1 Aerial Photography
On February 15 and September 9, 2008, Focal Flight (Ojai, CA) took 140 photographic images
of the Los Angeles and Long Beach Ports complex at a scale of 1:1600. Two cameras were
used simultaneously, one configured for natural color and one for near infrared (IR). The aerial
imagery flight was timed to coincide with the maximum low tide, optimum (high) sun angle, and
low wind conditions to optimize photo resolution and feature interpretation. The images were
then processed and geo-rectified using ESRI ArcMap 9.2 editing software to create a single
mosaic of the Ports complex. Mosaics were used to create a base image and initiation point for
evaluating the spatial extent of the upper edge of eelgrass communities and to document the
presence/absence of eelgrass within portions of the study area. The images were also georectified
in conjunction with 2005 orthographic images of the Ports areas to match up shoreline
features and delineate the observable boundaries of eelgrass beds.
8–2 2008 Biological Surveys of Los Angeles and Long Beach Harbors
April 2010