The plantings at the Alameda Creek areas 2 to 6 demonstrated that 

 (a) once established, cordgrass-mussel bioconstructs are highly resis- 

 tant to wave attack, (b) cordgrass-mussel bioconstructs will survive 

 transplanting, and (c) bioconstructs can be established in an area with 

 a fetch up to 7 kilometers without wave-stilling devices. 



VI. SUMMARY AND DISCUSSION 



Twenty-three natural intertidal cordgrass marshes in the San Francisco 

 Bay System had an average stem density of 650 per square meter and an 

 average stem height of 79 centimeters. These figures are compared to 

 those reported for natural smooth cordgrass marshes on the east coast. 

 Woodhouse, Seneca, and Broome (1974) reported an average density of 632 

 stems per square meter and an average height of 72 centimeters for 7 

 North Carolina marshes. 



Laboratory tests show that germination response in California cord- 

 grass is similar to that of smooth cordgrass (Seneca, 1974) . California 

 cordgrass seed should be harvested in late October and November and 

 stored in brackish water. Peak germination is reached in March, April, 

 and May, and freshwater is a stimulus to germination. 



It is difficult to describe wave environments where vegetative sta- 

 bilization is effective. There is no single theoretical way to determine 

 the formation of waves generated by winds in relatively shallow water 

 (U.S. Army, Corps of Engineers, Coastal Engineering Research Center, 

 1977). Fetch, windspeed, wind duration, and water depth are all major 

 determinants of wave climate. In addition, there are many physical and 

 biological variables that must be known to relate wave climate to plant 

 survival. The tidal elevation associated with a particular set of waves 

 and shore topography greatly influence the stress placed upon plantings. 

 Also, the ability of the plant to withstand waves depends on its growth 

 stage, density, and vigor, and the overall width of the planted area. 



For this study, fetch was used to qualitatively describe wave climate. 

 The frequency and speed of onshore winds are also important to wave cli- 

 mate analysis (Table 2). In general, the planting sites in this study 

 consisted of a shallow, gradually sloping offshore zone in front of 

 abruptly sloping banks. The success and failure of the California cord- 

 grass plantings exposed to various fetches are summarized in Table 7. 



Seeds were the least tolerant to wave attack and had no apparent 

 value in establishing cordgrass for erosion control. Plugs are more wave- 

 resistant than sprigs but were not successfully established on the 

 exposed sites. Sprigs and plugs may possibly be established on eroding 

 banks if adequate wave protection is provided. 



Plug transplants harvested from cordgrass-mussel communities are 

 extremely tolerant to wave activity. The ribbed mussels provide a mass 

 of fine byssal threads that attach to the root system of the cordgrass. 

 The compaction of cordgrass roots and dense mussel emplacements held 



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