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

8.0 Eelgrass
8.3.2.2 Pier 300/Seaplane Lagoon Area
Spring (March/April) 2008
The Pier 300 and Seaplane Lagoon area eelgrass beds occur in three physically distinct
locations (Figures 8.3-4 and 8.3-5). The first, “Seaplane Lagoon,” is an old Seaplane
anchorage that is located farthest from the harbor entrance. The second location, “Mitigation
Site,” is adjacent to Pier 300 and is the shallow water habitat mitigation site constructed as part
of the Pier 400 project, was planted in the winter of 2002/2003, and was augmented with
additional sediment and planting efforts in 2007 (Merkel & Associates 2008). This site is
comprised of dredge fill with rock revetments that created very shallow water habitat, suitable
for establishing an eelgrass bed. The third area, “Terminal Site,” is adjacent to a container
shipping terminal with a rock dike to the west and a small sandy beach to the north (Figure
8.3-4).
The Mitigation site, Seaplane Lagoon site, and Terminal Site contained a total of 30.7 acres of
eelgrass based on the March 2008 side-scan surveys. The Mitigation Site contained 15.4 acres
of eelgrass, with 4.8 acres mapped within the Seaplane Lagoon, and 10.4 acres of eelgrass
within the Terminal Site (Table 8.3-11). The Mitigation Site eelgrass bed was dispersed, but
with patches that appeared evenly spaced, as indicated by the data for transects M1 and M2
(Table.8.3-5). Associated algal species Chaetomorpha spp. and Gracillaria spp. that were
observed at the Cabrillo Beach area were also common within the Mitigation Site, near rocks or
shell piles, in conjunction with healthy patches of primarily large (2-3 ft) eelgrass plants growing
in uniform mud substrate. The majority of the eelgrass bed was in central portion of the
Mitigation Site (-6 ft to -8ft MLLW), but individual plants were observed throughout most of the
site. The lowest densities were noted on the far north portion of the site adjacent to the rock
jetty. Substrate was variable throughout the Mitigation Site with evidence of scouring and
patches of course shell fragments observed throughout the site, but most prominent near the
margins.
Turion counts at the Mitigation site in the spring varied widely from 0 to 6 turions per 1/16m 2
quadrat and typified the patchy nature of the eelgrass bed associated with this site (Table 8.3-
5). Divers performed two transects within the Mitigation Site in April, beginning in the center of
eelgrass beds identified during side-scan sonar surveys. Mean turion density (± standard
deviation) was low within the Mitigation Site and the Seaplane Lagoon compared to the nearby
Terminal Site (Table 8.3-5). Two areas adjacent to the surveyed transects, but not represented
in quadrat counts, had slightly higher densities based on diver observations (10 turions per
quadrat). Observations within the general Mitigation Site indicated dense and persistent red
algae (Gracillaria spp. and Prionitis spp.) growing within the eelgrass bed and commonly
intertwined with large mature eelgrass plants. Diver observations of eelgrass density, spatial
consistency, and associated algae provided important information utilized for sonar density
mapping interpretation.
The Seaplane Lagoon bed contained 4.8 acres of eelgrass during the April survey and
consisted of small fragmented linear patches from -1 ft to -7ft MLLW. Plants were sparse and
comprised of a mixture of small (6 in) and large (2-3 ft) individuals. The eelgrass beds within
the Seaplane Lagoon were variable, such that the low density habitat likely grades between a
defined eelgrass bed (at least one plant/m 2 ) under the SCEMP (NMFS 1991) and potential
eelgrass habitat (less than one plant/m 2 ). Substrate within the Seaplane Lagoon consisted of
fine mud.
In the spring turion counts at the Seaplane Lagoon were relatively low compared to other sites,
thereby illustrating the spatial variability and limited nature of the eelgrass bed in this area
2008 Biological Surveys of Los Angeles and Long Beach Harbors 8–7
April 2010