The best example of intolerance of 

 tropical seagrasses is their response to 

 heated effluents. The best known stan- 

 dards of how much heat could be released 

 (based on experience in temperate zone 

 rivers and offshore waters) were applied 

 to southern Florida. The test was a dis- 

 mal failure. South Florida has a much 

 more fragile ecosystem and organisms 

 could not withstand the same heat in- 

 creases that ecosystems in temperate wa- 

 ters could withstand. Government agen- 

 cies must be particularly careful at- 

 tempting to apply criteria of plant tol- 

 erance to trace metals or dredging in 

 temperate waters to situations in the 

 tropics, reasoning backwards from the 

 more complex temperate to the simple 

 ecosystem of the tropics. 



I would like very briefly to dis- 

 cuss the alternatives. I disagree with 

 Dr. Phillips' statement ("Creation of 

 Seagrass Beds" in this volume) that we 

 should plant Halodule rather than 

 Thalassia because Halodule grows faster. 

 I feel there are extremely important 

 unknowns yet to be determined about 

 restored Thalassia versus restored Halo- 

 dule before we can responsibly make that 

 statement. For example, does Halodule 

 support the same animal communities that 

 the Thalassia does? Most of the argu- 

 ments about restoration of seagrasses 

 are based on the fact that one is dis- 

 rupting the animal community, the fish- 

 eries potential, or the food web. We 

 have no evidence for this at all in the 

 case of Halodule because there has been 

 no intensive study on the animal commu- 

 nity associated with Halodule . There 

 have been many studies in various areas 

 on the animal community associated with 

 Thalassia . We do know that pink shrimp, 

 the stone crab, and many other desirable 

 animals leave (see Thorhaug and Roessler 

 1977 for a review or Thorhaug et al. 

 1973). 



A second question centers around 

 restoration of Halodule . Is one restor- 

 ing the same animals with a restored 

 Halodule community that one would be if 

 one restored Thalassia ? This is a dif- 

 ferent question from what is originally 

 in an untouched community of Thalassia . 

 A third question is, under various con- 

 ditions what is the Halodule root system 

 really going to do to stabilize the sed- 

 iment. Stabilization is one of the 



effects most desired in restoration, and 

 Halodule does not seem to function as 

 effectively as Thalassia as a sediment 

 stabilizer in regrowing areas. Fourth, 

 there are many areas where Thalassia is 

 just naturally not going to regrow so 

 there must be some effort to reestablish 

 Thalassia . In other places it may reseed 

 over a long period, but can we wait for 

 it to naturally reseed or revegetate? 

 My suggestion might be to plant a mixed 

 community in these semitropical and 

 tropical areas. In such a situation one 

 would not plant as much Thalassia be- 

 cause it is more expensive to plant than 

 Halodule . Halodule would start to form 

 a cover and then one would come back in 

 to restore Thalassia . 



The cost analyses that have been 

 done on the only scale experiments to 

 date are for Zostera and Thalassia . Zos- 

 tera was restored in England with the 

 free labor of prisoners and students. 

 Thus, the most expensive item, labor, 

 was avoided. This effort really repre- 

 sented a bare minimum. When added up, 

 it was about $2,500/ acre to actually 

 plant 2,000 turfs, so it was a large- 

 scale experiment. However, it should be 

 noted that it was done intertidally, 

 which is always less expensive than in 

 submerged areas. There was no formal 

 economic analysis of this, simply a 

 totaling of expenses. 



The Florida Board of Natural Re- 

 sources has attempted to restore Halo- 

 dule and Thalassia , for which they have 

 estimated that it is necessary to plant 

 186,000 plugs of Thalassia per acre in 

 order to get the kind of cover that the 

 Board of Natural Resources desires. Ac- 

 cording to their unpublished estimates 

 (Van Breedveld, personal communication) 

 which use minimum labor costs (which I 

 believe are unrealistic based on other 

 restoration efforts [see Terynk in these 

 proceedings] because you. are not going 

 to find people who will stand for 12 hr, 

 chest deep in freezing water, to plant 

 these seagrasses for $2.30), the cost 

 will be about $50,000 an acre by the 

 plugging method. 



Our estimates for Thalassia (given 

 in detail by Austin in Thorhaug and Aus- 

 tin 1977), based on about 7,000 Thalas- 

 sia having been planted in about 15,000 

 m2 using the seeding method, range at 

 the moment (depending on many factors, 



114 



