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

8.0 Eelgrass
load on the plants was mostly diatomaceous film and varied from low to moderate in most
areas.
Fall (September) 2008
Eelgrass coverage increased slightly in September in both the Cabrillo North and South areas
(Figure 8.3-3). Eelgrass coverage within both Cabrillo North and South totaled 38.2 acres. This
represents an increase of approximately 5% in eelgrass coverage among all areas within
Cabrillo Beach between April and September 2008. Eelgrass plant morphology changed
noticeably between survey periods with fall surveys reporting very few small (4-10 in.) plants
and the majority of plants ranging from 2-4 ft tall.
During September, 10.5 acres of eelgrass were recorded in Cabrillo South. The eelgrass bed
associated with this area was primarily along the shoreline out to the first swim buoy. Plants
observed on the inner and outer edges of the bed were patchy and widely spaced. Individual
plants were predominantly tall (2-4 ft) growing in uniform mud substrate, and several plants
showed evidence of new growth. The majority of the bed was observed in intermediate depths
of -3 ft to -8ft MLLW and consisted of plants with low epiphyte loads that were comprised of
diatom film and crustose coralline algae. Cover was patchy outside the main bed and quadrats
placed in a stratified-random manner along the transect line ranged in density from 0 to 128
turions/m 2 (Table 8.3-3).
Overall the eelgrass bed within the Cabrillo South area was sparse and patchy outside of a
defined band running parallel to shore, and Cabrillo South transect CS2a contained eelgrass
within only 6 of the 25 quadrats. Divers performed six transects within Cabrillo South, beginning
in the center of observed beds. Turion counts and corresponding densities were relatively low
compared to Cabrillo North, with the exception of transect CS1b (Table 8.3-3 and Table 8.3-4).
Mean leaf shoot (turion) density (± standard deviation) in the bed ranged from 4.60 ± 2.31
turions/m 2 to 73.6 ± 37.0 turions/m 2 (Table 8.3-3). Quadrat sampling by divers at this site was
increased between the April and September surveys in an attempt to more accurately quantify
the associated eelgrass beds observed during side-scan sonar surveys.
Turion counts were less dense in the fall than during the spring 2008 surveys; however, the
densities were consistent among bathymetric contours at Cabrillo North. Eelgrass acreage also
increased slightly. For example, during September 27.7 acres of eelgrass were recorded in
Cabrillo North - representing an increase of less than 3% from the spring. During the
September surveys six diver transects were performed within Cabrillo North (Figure 8.3-4).
Turion counts varied from 0 to 14 turions per quadrat, a reduction from April 2008. Densities
were relatively consistent throughout the eelgrass bed, with the exception of Cabrillo North
transect CN1a, nearest to the Cabrillo Marina jetty, where competing algae (Chaetomorpha
spp.) was dense within individual quadrats (Table 8.3-3). Mean turion density in the bed ranged
from 24.32 ± 31.71 turions/m 2 to 85.76 ± 33.59 turions/m 2 (Table 8.3-4). With the exception of
transect CN1a, densities were noticeably similar among all other Cabrillo North transects and
highlights the homogeneity of this eelgrass bed along bathymetric contours (Table 8.3-4).
Cabrillo North transects CN3a and CN3b were placed parallel to shore in the area of densest
eelgrass coverage and perpendicular to the April 2008 Cabrillo North transect CN2 location
(Figures 8.3-2 and 8.3-3). Plant size differences within Cabrillo North were much less evident
than observed during the April surveys, with very few small (4-10 in) plants observed. Hard
substrate (rocks) was observed in several locations along the transects. Gracillaria spp. and
Prionitis lanceolata was recorded in conjunction with eelgrass in several quadrats, with
Chaetomorpha spp. remaining prominent in the northern-most transects and noticeably
decreasing in occurrence moving south towards the boat ramp.
8–6 2008 Biological Surveys of Los Angeles and Long Beach Harbors
April 2010