together by the byssus threads provides an extremely firm, tightly bound 

 biotic community. Cordgrass-mussel bioconstructs survived (96 percent) 

 during the 13-month observation period at the Alameda Creek (area 4) . 

 This was a high-energy area, exposed to prevailing wind over a fetch of 

 6 to 27 kilometers. However, it is unlikely that this planting will 

 provide long-term stability to the bank. The density of shoots within 

 the bioconstructs declined throughout the observation period. The plants 

 at Alameda Creek (area 5) (7-kiloraeter fetch) have spread and will prob- 

 ably stabilize the shoreline. 



The estimate that California cordgrass can be established by plugs 

 in areas exposed to fetches of about 16 kilometers (Knutson, 1977) seems 

 to be overly optimistic. Plugs failed at Point Pinole despite the fact 

 that it was sheltered from prevailing winds and was exposed to a fetch 

 of only 14 kilometers. The poor survival of all propagules except the 

 cordgrass-mussel transplants suggests that California cordgrass is more 

 difficult to establish on eroding shores than its Atlantic coast counter- 

 part, smooth cordgrass. There is evidence that California cordgrass 

 does not grow and spread with the vigor of smooth cordgrass even when 

 planted in relatively sheltered areas. Plantings by the U.S. Army 

 Engineer District, San Francisco (1974) demonstrated that California 

 cordgrass requires 2 to 3 years to achieve densities comparable to 

 natural marshes in sheltered areas (U.S. Army Engineer District, San 

 Francisco, 1976; Morris and Newcombe, 1977). Researchers have reported 

 total cover in newly planted smooth cordgrass marshes within 1 to 2 

 years (Woodhouse, Seneca, and Broome, 1974; personal communication. Dr. 

 E.W. Garbisch, Environmental Concern, Inc., St. Michaels, Maryland, 1978), 

 Additional evidence concerning the relative growth of California and 

 smooth cordgrass resulted from laboratory studies conducted in Vicksburg, 

 Mississippi, by Barko and Smart (1976). California cordgrass plants 

 collected from the San Francisco Bay were compared with smooth cordgrass 

 propagules from Louisiana. Plants were grown at a salinity of 24 parts 

 per thousand in sand, silty clay, and clay with an artificially main- 

 tained tidal regime. Table 8 shows a comparison of ' the biomass of the 

 two species after 5 months. Smooth cordgrass growth was nearly twice 

 that of California cordgrass in sand, although growth was more than nine 

 times greater than California cordgrass in silty clay sediments and six 

 times greater in clay sediments. 



Despite apparent limitations, California cordgrass is suitable for 

 stabilizing relatively sheltered areas. Planting of sprigs and plugs is 

 likely to be effective only in sheltered coves, lagoons, and the mouths of 

 tributaries unless the plants are protected from waves. However, cord- 

 grass-mussel bioconstructs can be successfully established in areas 

 exposed to fetches of up to about 7 kilometers. 



35 



