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

8.0 Eelgrass
Areas containing eelgrass beds within the Port of Los Angeles appear to be constrained
primarily by physical factors associated with light and substrate, with distribution and abundance
documented intermittently since initial investigations were completed in the mid 1990s (Merkel &
Associates 2009 and MEC 2002). While the expansion of eelgrass to new locations throughout
the Port is possible, it is more likely that the eelgrass beds associated with Cabrillo Beach and
Pier 300/Seaplane Lagoon areas will continue to represent the most significant eelgrass areas.
Additional suitable eelgrass habitat likely exists in very small narrow bands along some of the
riprap and a small sparse area has recently been documented near Cabrillo Marina.
The 2008 eelgrass surveys documented eelgrass areas within expected locations and
confirmed consistent seasonal patterns among surveyed locations. Eelgrass beds displayed
seasonal changes in density and plant growth from spring to fall and dense mats of competing
marine algae associated with rock or shell fragments were observed at Cabrillo North and the
Mitigation Site in the Pier 300 area. The presence of Chaetomorpha spp. and Gracillaria spp.
within quadrats was noted at nearly every eelgrass area to varying degrees and was formed
dense mats up to 2 feet thick within the northern portion of the eelgrass bed at Cabrillo North
and near the margins of the Mitigation Site within the Pier 300/Seaplane Lagoon Area. The
degree to which the occurrence of these marine algae affects the spatial extent or density of
eelgrass beds within the Port is unknown. However, their common occurrence and density in
specific locations likely increases competition for space and/or light with existing and emerging
eelgrass plants.
The Cabrillo North eelgrass bed substrate was variable throughout the site with some hard
substrate (rock) observed within the northwestern and offshore portions of the bed. The
majority of the bed persists in fine mud and silt in shallow areas less than -7 ft MLLW and is
comprised of mostly small and evenly spaced plants, while deeper, offshore areas (> 8 ft
MLLW) were typified by large plants that were distributed randomly among sand/mud and shell
fragment substrates. The spatial extent of the Cabrillo North bed changed only slightly
(increased approximately 5%) between the spring and fall surveys (Table 8.3-10). Most notably
the bed extended to the south, connecting with the eelgrass bed at Cabrillo South, and the
densest areas expanded offshore in the fall (Figures 8.3-1 and 8.3-3).
The Cabrillo South area consists of fine sand/ mud substrate near the beach and mostly fine
silt/mud at deeper depths (> -6 ft MLLW). The inner edge of the eelgrass bed appeared well
defined, possibly from wave action or from recent sand movement. The spatial extent of the
Cabrillo South bed expanded from 9.33 acres in the spring to 10.5 acres in the fall (an increase
of approximately 12.5%) (Table 8.3-10). Most notably, the bed extended to the south, forming a
continuous bed along the shoreline that was not observed during the spring sampling and the
densest areas expanded and shifted offshore (Figures 8.3-2 and 8.3-3). Depending on yearly
fluctuations in recruitment and seasonal die-off in certain portions, the eelgrass bed at Cabrillo
South may become discontinuous and fragmented/patchy as apparent from the 2008 surveys.
Surveys conducted in the Pier 300/Seaplane Lagoon area showed three distinct eelgrass beds
or areas (Figure 8.3-4). The Seaplane Lagoon, located in a well-protected area in the
northeastern section, has limited flushing and fine sediments. Water quality appeared poor
during the surveys, with oil sheens and debris commonly observed on the surface and limited
water clarity during diver surveys, compared to the Terminal Site and Cabrillo North/South. The
spatial extent of the Seaplane Lagoon bed changed only slightly (decreased approximately 4%)
between the spring and fall surveys; the bed became more discontinuous in the fall and the
densest areas decreased noticeably (Figures 8.3-4 and 8.3-5). Nearly all observed eelgrass
was orientated parallel to shore within narrow bands between -4 and -7 ft MLLW. Epiphyte
loads were moderate and plants appeared randomly spaced and with little continuous bed
8–12 2008 Biological Surveys of Los Angeles and Long Beach Harbors
April 2010