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

7.0 Kelp and Macroalgae
sediment used to develop the shallow water habitat supported kelp in the spring (Figure 7.3-1)
but not during the fall surveys (Figure 7.3-3). Additionally, the kelp surface canopy associated
with the largest kelp bed near the entrance to Fish Harbor was noticeably reduced between the
spring and fall surveys (Figure 7.3-1 and 7.3-3). Similar differences in kelp canopy spatial
extent was observed in the Port of Long Beach between spring and fall, including reduced kelp
canopy cover and density near the boundary line between the Ports of Los Angeles and Long
Beach and a reduced width of delineated kelp canopy areas just shoreward of the Port of Long
Beach entrance (Figures 7.3-2 and 7.3-4).
The categorization of surface canopy densities within polygons provides a summary of the total
standing stock of kelp canopy observed during surveys and ultimately available for utilization by
associated invertebrates, fish, and wildlife.
Temporal fluctuations of kelp canopy cover and density within the Ports follow typical southern
California seasonal trends observed between late winter and early fall (Dayton et al. 1999, North
1994, among others). Factors affecting the degree of change of kelp canopy standing stock
within the Ports are complex but likely involve oceanic circulation and large-scale movements of
regional water masses within the Southern California Bight.
During the spring surveys, kelp plants appeared healthy, dense, and more closely spaced. Kelp
fronds (blades) contained low epiphyte loads and displayed few signs of stress or senescence.
Surveys of the same locations in fall found fewer, smaller kelp plants that were more widely
spaced and heavily infested with epiphytic bryozoans. Overall, kelp plants observed in the fall
had fewer stipes and fronds, thus showing signs of stress and deterioration. In kelp beds,
stratification in the water column during summer results in a warm, nutrient-poor environment
above the thermocline and cool, nutrient-enhanced conditions below (North 1983).
Consequently, kelp deterioration is greatest in the surface layers while basal portions may
survive with little, if any, damage. When sea surface temperatures fall during autumn, basal
portions may regenerate the canopies in a few weeks or months (North 1983). In addition, the
fall surveys may have been too early to document any basal regeneration. Nutrient availability
is negatively correlated with water temperature for values greater than 15.5°C (Zimmerman,
1983). Consequently, reported observations of summertime deterioration by Macrocystis
attributed to high temperature probably represent combined effects from elevated water
temperatures and low nutrients (Jackson 1977, Zimmerman and Kremer 1984).
The observed seasonal changes are to be expected in view of the elevated water temperatures,
reduced water circulation, and low nutrient concentrations typical of the summer months in
southern California, especially in enclosed bays and estuaries. Overall, seasonal decreases in
the extent and density of the kelp surface canopy also reduce primary and secondary
productivity, and habitat for associated biota. However, even though seasonal decreases are
evident, the persistence of some kelp canopy in the majority of surveyed areas stabilizes
community structure and species composition, increases the probability that more plants will
settle, and enhances recruitment of dependent invertebrates and fishes.
The Ports are near healthy kelp forests to the north, near Palos Verdes, that likely provide a
steady supply of sporophytes and gametophytes for colonization of suitable areas of the Ports.
For example, the 2000 baseline study noted relatively rapid colonization of kelp plants during
the construction of Pier 400 (MEC 2002). Similar recruitment events have been noted near
Cabrillo Marina, where substrate is commonly covered and uncovered by winter storms, thereby
making new suitable substratum available for settlement.
2008 Biological Surveys of Los Angeles and Long Beach Harbors 7–5
April 2010