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

7.0 Kelp and Macroalgae
(Figure 7.3-1 through 7.3-4). The kelp bed near the entrance to Fish Harbor was moderately
dense, with individual plants spaced approximately 1-2 meters apart. The surface canopy near
the Fish Harbor kelp bed and adjacent to the Federal Penitentiary (the rectangular peninsula
southwest of Fish Harbor) extended up to 30 meters away from the riprap in some places; M.
pyrifera in these locations appeared to be mostly perennial adults.
The macroalga Egregia menziesii occurred most commonly near the terminus of the outer
breakwater and along the western portions of the breakwall near Cabrillo Beach and the
entrance to the Port of Long Beach (Figure 7.3-1 and 7.3-2). Sargassum muticum, a non native
species (Abbott and Hollenberg 1976) was intermittently observed under piers and areas of low
wave exposure during vessel surveys. No spatial data for S. muticum was established because
occurrences of this species was limited to very small areas and typically occurred in conjunction
with the other dominant surface canopy species.
Sedimentation and scour are highly detrimental to kelp plants (Dayton 1985). On the other
hand, water movement is essential to kelp: motion resulting from tidal cycles, internal waves,
and alongshore currents replenishes dissolved nutrients within kelp beds and removes waste
products (North 1994). Kelp and macroalgae communities near the harbor entrances (outer
harbor) likely benefit from increased water clarity, lower water temperatures, and less turbidity
than stations farther into the harbors (inner stations) with lower water clarity and higher turbidity.
The combination of proximity to the harbor entrance and the presence of extensive hard
substratum likely explains the abundance of kelp and macroalgae associated with the Cabrillo
Shallow Water Habitat (CSWH; Figures 7.3-1 and 7.3-3).
7.3.2 Temporal Variability
Global distribution of kelp forests is
physiologically constrained by light at high
latitudes and by nutrients, warm
temperatures, and other macrophytes at low
latitudes (Steneck et al. 2002). Other
important environmental factors influencing
kelp communities include available substrata,
sedimentation, water motion, and salinity.
(Dayton 1985). Temporal unpredictability,
especially episodic recruitment events,
should be considered characteristic of kelp
(Dayton and Tegner 1984). Annual
variations in surface kelp canopy coverage
area and density have important implications
to the associated community within kelp
beds.
Temporal variability of surface kelp canopy was evident within the Ports during the 2008 spring
and fall sampling events, similar to those noted during the 2000 baseline sampling. During the
2008 spring surveys, total surface canopy cover of M. pyrifera and E. menziesii was 77.8 acres
and 2.33 acres, respectively (Figures 7.3-1 and 7.3-2). By fall, the cover of M. pyrifera had
declined markedly, to 50.41 acres and E. menziesii decreased to approximately 2.12 acres
(Figures 7.3-3 and 7.3-4). In addition to declines in the extent of canopy coverage, the density
of the kelp beds declined between spring and fall (Table 7.3-1).
Variations in the M. pyrifera surface canopy were especially dramatic between the spring and
fall 2008 surveys throughout the CSWH: linear subtidal rock dikes installed to stabilize the soft
7–4 2008 Biological Surveys of Los Angeles and Long Beach Harbors
April 2010