11. Submerged Aquatic Vegetation (SAV) as a Management Objective (Designated Use) 
11.1 Background 
The NHEERL Aquatic Stressors Framework (U.S. EPA, 2002) defines loss of submerged 
aquatic vegetation (SAV) as a major assessment endpoint for nutrient effects research. Seagrass, the 
dominant marine SAV, provides a critical three-dimensional structure often used by commercially and 
ecologically important species as a refuge from predation, and simulates estuarine biogeochemical 
cycling through trapping and recycling of seston and leaf material in sediments. Seagrasses also 
influence water quality and clarity by attenuating current velocity, promoting sediment deposition, and 
removing nutrients (N and P) from the water column. Thus, seagrass habitats function in a way that 
improves the quality of coastal and estuarine ecosystems. Sustaining seagrasses has become an 
important priority for federal agencies, the States, and tribes. 
Eelgrass ( Zoster a marina ), the principal seagrass in PNW estuaries (Phillips, 1984), is a rooted, 
flowering plant, which is present in many temperate estuaries world wide (den Hartog, 1970). Eelgrass 
meadows serve as a nursery ground for juveniles of commercially important species such as Pacific 
herring ( Clupea pallassi) and as a refuge for juvenile salmonids (Griffin, 1997; Simenstad and 
Wissmar, 1985; Levings, 1990; den Hartog, 1977). Eelgrass meadows are significant sites of primary 
production and eelgrass shoots can be utilized directly for food by some waterfowl such as the western 
black brant {Branta bernicula) (Griffin, 1997; Kentula and Mclntire, 1986), and indirectly by many 
species via consumption of detritus (Thayer et al., 1975). Eelgrass roots stabilize the sediment (Thayer 
et al., 1975) and the presence of eelgrass dampens wave energy which may serve to reduce erosion and 
to enhance larval settlement (Orth, 1992). Because of these characteristics, species abundances in 
eelgrass patches are usually greater than in other estuarine habitats (Everett et al., 1995). In 
recognition of the importance of seagrass beds, EPA Region III has proposed a “Shallow-water Bay 
Grass Designated Use” for Chesapeake Bay to insure adequate protection of living resources. 
Anthropogenic nutrient additions have been suggested by many authors as a cause for the 
dramatic decline in seagrasses world wide and for Z. marina in particular on Atlantic Coasts (Short et 
al., 1995: Valiela et al 2000a; Hauxwell et al., 2003). The principal effect of excess nutrients is to 
reduce light available at leaf surfaces via enhanced macroalgal and leaf epiphyte production and by 
increasing the water column light attenuation coefficient (kd) through the stimulation of the production 
of phytoplankton (Hauxwell et al, 2001; Madden and Kemp, 1996). 
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