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

8.0 Eelgrass
8.5 HISTORICAL COMPARISONS
Based on the multitude of physical and biological factors shaping eelgrass community growth,
recruitment, and productivity, the Ports’ 2008 eelgrass surveys should be viewed in a regional
and historical context. While seasonal differences between the 2008 spring and fall surveys
were not significant in terms of changes in the spatial extent of eelgrass, they reinforce the need
to examine trends from broader time scale and regional perspective. The examination and
evaluation of eelgrass communities throughout southern California has increased significantly
since 1990 and provides expanded data sets of similar eelgrass systems that should be
considered when evaluating trends in eelgrass distribution within bays and harbors.
Surveys of eelgrass resources within the Ports study area were conducted for the Port of Los
Angeles in 1996 and again in 1999 by the Southern California Marine Institute (SCMI) and in
both Ports for the 2000 baseline study (MEC 2002). The 1996 report only covered eelgrass
areas at Cabrillo Beach, while the 1999 report looked at both Cabrillo Beach and the Pier 300
Shallow Water Habitat (Gregorio 1999). The 2000 baseline study surveyed all waters of both
Ports for eelgrass, and was conducted prior to eelgrass transplantation at the Pier 300 shallow
water habitat mitigation site, which was completed in the winter of 2002/2003. Survey methods
utilized during the 1996 and 1999 investigations did not include side-scan sonar imagery, but
provide important data records on the areal extent and turion density within eelgrass areas
delineated during the present (2008) study and the 2000 baseline study. Considering the
discontinuous nature of the eelgrass data sets available for the Port of Los Angeles, the
combined data sets provide generally limited information on site-specific eelgrass trends.
Equally important to site-specific eelgrass distribution and density variations within the study
area are their relationship to regional trends documented in other bays and harbors throughout
southern California.
Data sets available on the areal extent of eelgrass within the Ports are most comprehensive for
the Cabrillo Beach areas (Figure 8.3-6). Off Cabrillo Beach, a total of 24.6 acres of eelgrass
was reported in 1996 (season unknown), increasing to 54.5 acres in October 1999 (Gregorio
1999). The 2000 baseline survey reported 42.3 acres of eelgrass within the Cabrillo Beach area
in August 2000 and the 2008 baseline survey mapped 26.7 acres within the same location.
Differences in the spatial extent of eelgrass within the Port of Los Angeles between the 2000
and 2008 baseline surveys are attributed to natural variability and, to a lesser extent, changes in
hydrology. The existing data sets provide sufficient trend data for comparisons with other bay
and estuarine eelgrass data and compares favorably with trend data collected in San Diego
Bay. Eelgrass data from San Diego Bay provides a more long-term and comprehensive basis
for comparing changes in eelgrass distribution and abundance in a southern California harbor
environment. In order to help understand relative trends in the areal extent of Port of Los
Angeles/Long Beach eelgrass communities, San Diego Bay eelgrass communities are
presented for comparison in Figure 8.3-8.
Factors that influence eelgrass growth, reproduction, and health can be somewhat localized, but
also can be driven by regional water masses and weather conditions that are broadly applicable
within the Southern California Bight. The increase in eelgrass coverage observed at Cabrillo
Beach between 1996 and 1999/2000 was approximately 72% while San Diego Bay reported an
increase of 57% between 1994 and 1999 (Figure 8.3-8). San Diego Bay investigations reported
an additional expansion of 27% between 1999 and 2004 followed by a decrease of 37%
between 2004 and 2008. In relative terms, the Port of Los Angeles Cabrillo Beach eelgrass
coverage follows a similar trend to that of San Diego Bay, although without any data for
comparison with the 2004 trend in San Diego Bay. Eelgrass coverage and health is well
documented as being adversely affected by ENSO events in 1997/1998 and displayed
substantial recovery during 1999 (Merkel & Associates 2000). The 2000 baseline study (MEC
2008 Biological Surveys of Los Angeles and Long Beach Harbors 8–15
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