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

8.0 Eelgrass
8.0 EELGRASS
8.1 INTRODUCTION
The primary objective of this task
was to characterize the occurrence
of eelgrass beds within the Ports of
Los Angeles and Long Beach (Ports)
and compare changes in eelgrass
bed extent and density since the last
baseline survey (MEC 2002).
Seagrasses (Spermatophyta) inhabit
soft bottom habitat, and the
extensive meadows they form rank
among the most productive coastal
ecosystems in the world (McRoy and
McMillan 1977). Of the three
separate species of seagrass
(Zostera marina, Z. pacifica, and Z.
asiatica) that have been observed in
the Southern California Bight (SCB),
eelgrass (Zostera marina) is the most common species occurring in embayments (Dailey et al.
1993).
Eelgrass is an aquatic angiosperm distributed sporadically in bays, estuaries, and within
offshore beds throughout the majority of the Northern Hemisphere. Along the west coast of
North America, eelgrass is found from southeastern Alaska to southern Baja California and
Mexico, typically in protected bays and estuaries from the low intertidal to a depth of
approximately 20 meters (m) (Green and Short 2003). Eelgrass beds create a defined
community structure for a wide variety of aquatic organisms and perform important physical and
biological functions that allow for the persistence of highly productive habitat. Eelgrass beds
function as habitat and nursery areas for commercially and recreationally important marine fish
and invertebrates, and provide critical structural environments for resident bay and estuarine
species (Hoffman 1986, Kitting 1994). Their function as nursery areas for fish and invertebrates
and as foraging grounds for many marine bird species make eelgrass beds highly valuable as a
marine resource far beyond their physical extent.
Eelgrass is important both ecologically and economically, representing a key species in
maintaining healthy coastal and estuary ecosystems (Davis et al. 1998, Gayaldo et al. 2001,
and Williams 2001).
Eelgrass reproduces sexually through seeds and asexually through horizontal rhizomes and leaf
shoots. Although dispersal of pollen and individual seeds is limited, genetic studies have shown
that the seed-bearing spathes can be transported from one area to another via rafting of
detached plants or inflorescences (Reusch 2002). Although considerable attention has been
given to limitations of seagrass growth by variability in light, temperature, and nutrients (e.g.,
McRoy and McMillan 1977, Orth 1977, Williams and McRoy 1982, Dennison and Alberte 1985,
and Dennison 1987), growth is affected by a more complex array of factors including hydrology,
grazing, and epiphytic growth (Fonseca and Kenworthy 1987, Thayer et al. 1985, Williams and
Carpenter 1988, Williams and Ruckelshaus 1993). As water quality in many bay and coastal
environments declines due to increases in anthropogenic nutrient and sediment loading, the
2008 Biological Surveys of Los Angeles and Long Beach Harbors 8–1
April 2010