appendix b final 2008 biological surveys of los angeles and long ...
appendix b final 2008 biological surveys of los angeles and long ...
appendix b final 2008 biological surveys of los angeles and long ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
8.0 Eelgrass<br />
formation evident. While this bed appears persistent from previously reported observations,<br />
seasonal differences in eelgrass bed extent were apparent from the side-scan <strong>surveys</strong>.<br />
The Mitigation Site located in the center <strong>of</strong> the Pier 300/Seaplane Lagoon Area consisted <strong>of</strong><br />
large, evenly spaced plants with occasional dense patches that were less than 3 m 2 . Red algae<br />
(Chaetomorpha spp. <strong>and</strong> Gracillaria spp.) was commonly observed as potential competitors for<br />
space <strong>and</strong> light among the eelgrass plants <strong>and</strong> was particularly evident adjacent to the rock<br />
revetments <strong>and</strong> in areas with hard substrate (rock) or shell fragments. The southern portions <strong>of</strong><br />
the Pier 300 site contained higher densities <strong>of</strong> Gracillaria spp., to the extent that it was much<br />
more common than the eelgrass plants. Considering the Mitigation Site is composed <strong>of</strong> rock<br />
revetments constructed to support the dredge fill <strong>of</strong> various sizes, the occurrence on marine<br />
algae is not surprising based on the available substrate. Considering the location <strong>of</strong> the<br />
Mitigation Site between the small s<strong>and</strong>y beach embayment to the west, comprised <strong>of</strong> mostly fine<br />
s<strong>and</strong> <strong>and</strong> mud, <strong>and</strong> the deep dredged channel leading into the Seaplane Lagoon, circulation<br />
<strong>and</strong> scouring from tidal water movement likely contribute to the occurrence <strong>of</strong> courser sediments<br />
<strong>and</strong> the persistence <strong>of</strong> competitive algal species. Previous eelgrass transplantation that was<br />
conducted in 2003 <strong>and</strong> 2007 still appears spatially distinct <strong>and</strong> the associated eelgrass<br />
community is likely being shaped by the complex interactions <strong>of</strong> competition <strong>and</strong> hydrology that<br />
affects sediment distribution.<br />
The eelgrass bed within the Mitigation Site displayed very little season change, decreasing from<br />
15.4 acres in the spring to 15.1 acres in the fall (approximately 2.5%). The low density <strong>and</strong><br />
evenly spaced plants observed throughout this site coupled with dense aggregations <strong>of</strong><br />
Gracillaria spp. made evaluations <strong>of</strong> the differences in sonar <strong>surveys</strong> difficult. For example,<br />
although the imagery shown in Figures 8.3-4 <strong>and</strong> 8.3-5 depicts a continuous low density bed,<br />
the actual configuration <strong>of</strong> the site is likely more fragmented at a finer scale.<br />
The Terminal Site in the western most portion <strong>of</strong> the Pier 300/Seaplane Lagoon area is the most<br />
consistent eelgrass habitat within this portion <strong>of</strong> the Port <strong>and</strong> consists <strong>of</strong> uniform s<strong>and</strong>/mud<br />
substrate supporting a continuous, healthy bed <strong>of</strong> eelgrass with only intermittent occurrences <strong>of</strong><br />
algae (Chaetomorpha spp. <strong>and</strong> Gracillaria spp.). The Terminal Site extends from the s<strong>and</strong>y<br />
beach adjacent to the Mitigation Site to the south a<strong>long</strong> the riprap. The spatial extent <strong>of</strong> the<br />
Terminal Site bed decreased from 10.4 acres in the spring to 8.9 acres in the fall (approximately<br />
15%), with the bed contracting throughout the <strong>of</strong>fshore edge <strong>and</strong> the densest areas decreased<br />
overall (Figures 8.3-2 <strong>and</strong> 8.3-4). Seasonal differences in plant sizes were evident with the<br />
eelgrass bed a<strong>long</strong> the beach shifting from small <strong>and</strong> large plants in the spring to mostly large<br />
(>2 ft) plants in the fall, with a low epiphyte load. During both spring <strong>and</strong> fall <strong>surveys</strong> the<br />
eelgrass was evenly spaced, forming a continuous bed just inshore <strong>of</strong> a noticeable berm at<br />
approximately -5 to -8 ft MLLW. Extending south a<strong>long</strong> the riprap adjacent to the terminal, the<br />
substrate contained several dark areas <strong>of</strong> fine mud where the eelgrass bed became increasing<br />
discontinuous <strong>and</strong> sparse moving away from the beach <strong>and</strong> the riprap.<br />
In some cases considerable annual (seasonal) variation in abundance has been documented in<br />
southern California (e.g., winter die-<strong>of</strong>f <strong>and</strong> spring/summer re-growth) due to a variety <strong>of</strong> factors,<br />
including but not limited to physical <strong>and</strong> <strong>biological</strong> disturbance, changes in nutrient availability,<br />
<strong>and</strong> changes in water quality parameters such as turbidity <strong>and</strong> salinity. These factors can result<br />
in <strong>long</strong>-term changes in eelgrass abundance depending on the frequency <strong>and</strong> intensity <strong>of</strong><br />
unfavorable conditions. Eelgrass density also can vary substantially depending on the bottom<br />
depth <strong>of</strong> plant attachment. This is due to variations in the size <strong>of</strong> plant turions at different<br />
depths. For example, at shallower depths eelgrass density is typically greater than at deeper<br />
depths (Durance 2002 <strong>and</strong> Gussett 2002). Eelgrass density <strong>and</strong> morphology vary with respect<br />
to depth, exposure, substrate, <strong>and</strong> water clarity (Durance 2002). As a result, it can be difficult to<br />
define characteristics for a “normal” eelgrass bed.<br />
<strong>2008</strong> Biological Surveys <strong>of</strong> Los Angeles <strong>and</strong> Long Beach Harbors 8–13<br />
April 2010