on the cost of the effort. Neverthe- 

 less, the first decision should be based 

 strictly on the biological rationale and 

 only after this decision is made should 

 economic considerations and compromises 

 be considered. To plant the wrong spe- 

 cies because of economic considerations 

 might do more harm than good. 



Often the cost considerations will 

 cause a compromise between size of re- 

 stored area and what is planted. In my 

 opinion, if cost is the determining fac- 

 tor, it is better to restore a smaller 

 area correctly than a large area incor- 

 rectly. An exception would be when sed- 

 iment stabilization is the only goal. 



The density to be achieved and the 

 time period are highly dependent on den- 

 sity of seagrasses currently present in 

 the area. The usual case would be to 

 reestablish the same density within a 

 reasonable time scale of about 3 to 6 

 yr. If the ultimate density is to be 

 established in a very short time scale 

 (such as months), the cost may become 

 economically unfeasible (Thorhaug and 

 Austin 1977). Note that the question of 

 what density is present is a seasonal 

 consideration in most areas, with late 

 spring peaks and winter lows (Thorhaug 

 and Roessler 1977). Use the highest sea- 

 sonal density in the estimations. 



Spatially the density of the sea- 

 grass may not be even throughout the 

 area. One might choose an average den- 

 sity of the entire area as the restora- 

 tion goal, but it is more advisable to 

 restore the area in several different 

 densities. If, for instance, a near- 

 shore peat wedge sustains a higher 

 standing crop than offshore sediment, it 

 should be restored in that ratio. The 

 time period for recovery to a given den- 

 sity is a function of the rate of growth 

 of the plants. (Seagrasses spread lat- 

 erally by rhizomal growth.) This rate 

 is highly dependent on species and envi- 

 ronmental conditions and mu£t be envi- 

 ronmentally determined. Best estimates 

 are achieved when a pre-impact growth 

 study has been done in that area. 



The remainder of this article dis- 

 cusses rationale, historical detail, 

 methods, results, and economic cost anal- 

 ysis of planting seagrasses. More infor- 

 mation can be found in Thorhaug and Aus- 

 tin (1977) and Thorhaug (1977). 



INTRODUCTION TO THE IMPORTANCE 

 OF SEAGRASSES 



Although the marine environment is 

 thought to be a place of high productiv- 

 ity, a great portion of the ocean has 

 very low or no productivity. There are 

 a few "hot spots," such as upwel lings 

 which provide a good deal of the total 

 productivity of the oceans. Among these 

 "hot spots" are the seagrass beds which 

 colonize coastal areas of the marine en- 

 vironment. There are 12 genera of angio 

 sperms which have adapted to the marine 

 environment. Eel grass ( Zostera marina ) 

 and turtle grass ( Thalassia testudinum ) 

 are dominant, respectively, in the U.S. 

 temperate and tropical to subtropical 

 zones. On the east coast of the U.S. 

 Zostera dominates southward to South 

 Carolina. In Florida and the Gulf of 

 Mexico Thalassia dominates, interspersed 

 with Syrinqodium and Halodule . 



Seagrasses function in the marine 

 environment in several ways. First, they 

 produce a great deal of organic carbon, 

 much of which enters the food chain both 

 by direct feeding and by detritus. Pro- 

 duction estimates are 300 to 600 g dry 

 weight per meter per year for turtle 

 grass (Thorhaug and Roessler 1977). 

 Secondly, the seagrass provides a shel- 

 ter and place of attachment for many 

 small animals which form the seagrass 

 community. Third, the roots of the sea- 

 grass systems bind the sediment and also 

 provide a baffle for particles so that 

 they enhance the stability of the sedi- 

 ment beneath them, as well as the clar- 

 ity of the water. And lastly, they act 

 as a nutrient and trace metal cycling 

 system for various elements in the 

 marine environment. 



Recently, there has been a series 

 of studies on the ecology of both the 

 temperate species Zostera and subtropi- 

 cal species Thalassia [Phillips 1960, 

 1972; den Hartog 1972; Thorhaug 1974; 

 Thayer et al. 1975; McRoy and Helfferich 

 1979; Thorhaug and Roessler 1977). Sev- 

 eral points of the ecology are important 

 to restoration efforts. The seagrasses 

 are found in the coastal regions of the 

 world; high densities are usually found 

 close to shore, particularly in bays, 

 estuaries, and lagoons. The densest 

 stands of seagrass occur very close to 



106 



