the closed system, however. Thorhaug 

 et al . (1973) found little evidence of 

 damage to the biota of Card Sound, partly 

 because effluent temperatures there were 

 lower than those experienced in Biscayne 

 Bay, and even before the thernal addi- 

 tions, the benthic community of the af- 

 fected portion of Card Sound was rela- 

 tively depauperate compared to Biscayne 

 Bay. 



The temperatures and salinities of 

 the bays and lagoons of south Florida show 

 iiiuch variation, and the fauna and flora 

 must have adequate adaptive capacity to 

 survive. Although the heated brine ef- 

 fluent from the Key West desalination 

 plant caused marked reduction in the 

 diversity in the vicinity of the outfall, 

 nearly all beds of turtle grass were unaf- 

 fected (Chesher 1975). Shoal grass is the 

 most euryhaline of the local seagrasses 

 (^lc^!^llan and Moseley 1967). Turtle grass 

 and manatee grass show a decrease in 

 photosynthetic rate as salinity drops 

 below full strength seawater. The season- 

 ality of seagrasses in south Florida is 

 largely explained by temperature and 

 salinity effects (Zieman 1974). The 

 greatest decline in plant populations was 

 found when combinations of high tempera- 

 ture and low salinity occurred sii;iultan- 

 eously. Tabb et al . (1962) stated: "Most 

 of the effects of man-made changes on 

 plant and animal populations in Florida 

 estuaries (and in many particulars in 

 estuaries in adjacent regions of the Gulf 

 of Mexico and south Atlantic) are a result 

 of alterations in salinity and turbidity. 

 High salinities (30-40 ppt) favor the sur- 

 vival of certain species like sea trout, 

 redfish and other marine fishes, and 

 therefore improve angling for these spe- 

 cies. On the other hand these higher 

 salinities reduce survival of the young 

 stages of such important species as com- 

 mercial penaeid shrimp, menhaden, oysters 

 and others. It seems clear that the 

 balance favors the low to moderate salin- 

 ity situation over the high salinity. 

 Therefore, control in southern estuaries 

 should be in the direction of maintaining 

 the supply of sufficient quantities of 

 fresh water which would result in estua- 

 rine salinities of 18 to 30 ppt." 



Perhaps reduced v/ater flow in the 

 Everglades has had unexpected impacts in 



seagrass beds. The eastern regions of 

 Florida Bay were formerly characterised by 

 low salinity, muddy bays with sparse 

 growths of shoal grass. Fishing here was 

 often excellent as a variety of species 

 such as mullet and sea trout foraged in 

 the heterogenous bottom. One of the main- 

 stays of the fishing guides of this area 

 was the spectacular and consistent fishing 

 for redfish. In recent years the guides 

 have complained that this fish population 

 has become reduced, and it is not worth 

 the effort to bring clients to this area. 

 In January 1979 this author took a trip 

 through this region and found that much of 

 the formerly mud and shoal grass bottom 

 that he had worked on 10 to 12 years prior 

 was now lush, productive turtle grass 

 beds. Where the waters were once muddy, 

 they were now, according to the guide, 

 much clearer and shallower, but provided 

 less sea trout and redfish. Why? The 

 following hypothetical scenario is one 

 explanation. 



In the late sixties the infamous 

 C-111 or Aerojet-General canal was built 

 in south Dade County, on which Aerojet 

 hoped to barge rocket motors to a test 

 site in south Dade. The contracts failed 

 to materialize and the canal, although 

 completed, was left plugged and never 

 opened to the sea. Its effect, however, 

 was to intercept a large part of the over- 

 land freshwater flow to the eastern Ever- 

 glades and ultimately to eastern Florida 

 Bay. 



The interception of this water is 

 thought to have created pronounced changes 

 in the salinity of eastern Florida Bay, 

 allowing for much greater saltwater pene- 

 tration. As the salinity increased, tur- 

 tle grass, which had been held in check by 

 lowered salinity, may have had a competi- 

 tive advantage over shoal grass and 

 increased its range. The thick anastomos- 

 ing rhizome mat of turtle grass stabilized 

 sediments and may have made foraging dif- 

 ficult for species that normally grub 

 about in loose mud substrate. Also the 

 greater sediment stabilizing capacity of 

 turtle grass may have caused rapid filling 

 in an environment of high sediment supply 

 and low wave energy. 



This scenario has not been proven; 

 thus it is hypothesis and not fact. It 



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