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

8.0 Eelgrass
at Cabrillo South. The eelgrass bed at Cabrillo South was located primarily along the shoreline
out to the first swim buoy, but also included isolated eelgrass beds to the east of the main bed,
along the north facing portion of the swim beach. The eelgrass bed extended from 0.0 to -10 ft
MLLW. Plants observed on the outer (deeper – 8ft MLLW) edge were generally small (8-10
inches), interspersed with larger (2-3 ft) plants growing in uniform mud substrate, and several
plants appeared to represent new growth. The majority of the bed was limited to shallower
areas (-6 ft MLLW to -3ft MLLW) of fine sand/mud substrate and consisted of large (2-3 ft) tall
plants with a low to moderate epiphyte load. Cover was patchy outside the main bed and data
from stratified random quadrats along the transect line varied in density from 0 to 208/m 2 .
Turion counts varied widely from 0 to 13 turions per quadrat and the beds were patchy (Table
8.3-1). Divers performed two transects at Cabrillo South, beginning in the center of observed
beds. Mean turion density (± standard deviation) in the bed ranged from 49.3 ± 44.5 turions/m 2
for transect CS1 to 97.9 ± 53.1 turions/m 2 for transect CS2. Mean turion density varied between
transects primarily based on the absence of turions within several quadrats near the terminus of
transect CS1. Transect CS1 was performed perpendicular to shore to evaluate the deeper
edge of the eelgrass bed. These data illustrate that the several quadrats containing no plants
strongly influenced conclusions of low mean density and high standard deviation along this
transect.
The Cabrillo North eelgrass was expansive and diverse, consisting of various depth gradients,
plant sizes, and exposure aspects. Cabrillo North extends from the Cabrillo boat launch ramp
north to the jetty of Cabrillo Marina (Figure 8.3-2). The eelgrass bed in this area measured 17.4
acres in April 2008 and extended from 0 to -12 ft MLLW. Adjacent to the launch ramp and at
the outflow of the salt marsh, this bed was composed of dense, short eelgrass (4-10 inches tall),
was observable at low tide (tide -0.2 ft @12:58 PM), and appeared uniform in distribution on
sand/mud substrate. The eelgrass bed at this location was the largest and most consistent of
all beds surveyed during the 2008 study. The northern portion of the bed beginning near the
Cabrillo marina jetty was thick and continuous along a -4 ft MLLW depth contour and was
comprised of plants that were 2-3 ft tall with a moderate epiphytic load. Areas surveyed
between the Youth Facility pier and the jetty contained dense mats of the green alga
Chaetomorpha spiralis (hereafter Chaetomorpha) intertwined with the eelgrass plants.
Chaetomorpha mats varied from 6 inches to 2 ft thick along the bottom and complicated the
turion density counts. The red alga, Gracillaria spp. (likely G. veleroae), was also present within
the eelgrass beds at Cabrillo North and was most common within the far northern portions of the
bed adjacent to the Cabrillo Marina jetty.
The diver transect results were consistent with the observations above regarding the density
and extent of eelgrass meadows at Cabrillo North. During the April surveys, two diver transects
were performed within Cabrillo North. Turion counts varied from 1 to 17 turions per 1/16m 2
quadrat, but were relatively consistent throughout the eelgrass bed (Table 8.3-2). Mean turion
density among Cabrillo North transects was relatively consistent based on the moderate to low
standard deviations of the transect data and observed homogeneous nature of the bed. Mean
turion density (± standard deviation) in the bed was 143.4 ± 54.4 turions/m 2 for Cabrillo North
CN1 and 122.2 ± 35.1 turions/m 2 for CN2, highest among all sampled transects (Table 8.3-2).
One transect, Cabrillo North CN2, was performed perpendicular to shore to evaluate the
consistency of the eelgrass bed throughout its depth range, as the bed extends well offshore
based on sonar observations. Plants within the quadrats appeared to increase in size moving
offshore. Observations beyond the eelgrass bed surveyed at Cabrillo North CN2 noted that the
eelgrass bed extended offshore more than 50 m beyond the swim buoys and became patchy
with lower densities. Size differences were evident throughout much of the Cabrillo North area
with small plants (6 inches) sometimes growing adjacent to larger (2 ft +) plants. The epiphytic
2008 Biological Surveys of Los Angeles and Long Beach Harbors 8–5
April 2010