at Sand Key. Enos (1977) and others 

 (Shinn 1966, Antonius 1977, Mars- 

 zalek et al. 1977) suggest that such 

 short-term temperature drops serve 

 more to limit a coral's geographical 

 range and affect its yearly via- 

 bility than long-term temperature 

 averages (monthly mean) typically 

 reported. 



Spatial variation of salinity 

 along the longitudinal axis of the 

 reef tract is less than observed for 

 temperature; however, the data base 

 reviewed is also more sporadic. 

 Davis (1940) reports salinity data 

 for the area's water for the years 

 1936 to 1938, and although the data 

 base is severely limited in scope 

 and duration it provides an inter- 

 esting perspective on temporal and 

 spatial changes in 

 (1936) and 'dry' 

 As shown in Table 

 Florida and the Dry Tortugas sta- 

 tions exhibit salinities intermedi- 

 ate (36%) to those observed in the 

 Gulf (33%) and the Atlantic (37%). 



response to 'wet' 

 (1937-38) years. 

 19, the Straits of 



No. 

 Samples 



Salinity (ppt ) 

 1937 1938 



Atlantic Ocean 5 



Straits of Florida 16 



Tortugas 12 



Gulf of Mexico 10 



37.0 

 35.7 

 35.8 

 31.7 



36. B 

 36.2 

 35.7 

 33.1 



37.1 

 37.8 

 36.1 

 32.5 



Average 



37.0 

 36.2 

 35.9 

 32.6 



Table 19. Average salinity of 

 open sea nearshore 

 waters associated 

 with the Florida Keys 

 (adapted from Davis 

 1940). 



Table 20 summarizes salinity 

 data from studies more specific to 

 the outer reef tract. Salinity 



generally ranges between 36 ppt and 

 38 ppt, particularly off the upper 

 and lower reef systems. The more 



northern locations, Fowey Rocks and 

 Triumph Reef (Elliott Key) exhibit 

 lower salinities in response to 

 inflow from Biscayne Bay. The Dry 

 Tortugas, like the northern reefs, 

 exhibit lower salinities, responding 

 in this case to the Gulf Loop Cur- 

 rent's entrained continental shelf 

 waters (Wennekins 1959). The Gulf 

 Loop Current's waters occassionally 

 expose the lower Keys' reef system 

 to sudden drops in salinity, as 

 observed by Jaap and Wheaton (1975) 

 on East and West Sambo Reefs. Moni- 

 tored from March 1973 to August 

 1974, the salinity remained at a 

 constant 37 ppt except during August 

 1973, when the salinity dropped to 

 33 ppt. 



Location 

 Fowey Rocks 

 Triumph Reef 

 Margot Fish Shoal 

 Key Largo-Outer Reefs 

 Lower Keys-Outer Reefs 

 w & E. Sambo Reef 

 Key West-Fore Reef 

 Dry Tortugas 

 •see text 



Salinity Range (ppt) 



34.2 - 38.6 



35.3 - 36.5 

 36.8 - 37.3 

 36.6 - 36.9 

 36.0 - 38.0 

 37.0 - (33)« 

 36.0 - 37.0 

 35.2 - 36.1 



Source 

 Dole A Chambers 1918 

 Smith et al. 1950 

 Jones 1963 

 Hanker 1975 

 Kissling 1977 

 Jaap & Wheaton 1975 

 Chew 1954 

 Dole 1914, Davis 1940 



Table 20. Salinities reported for 

 the Florida reef tract 

 and vicinity. 



Turbidity along the Florida 

 Keys seaward environment is, like 

 temperature and salinity, dependent 

 on the degree of mixing with the 

 Florida Bay and Gulf Loop Current 

 water masses (Ginsburg 1956). Wa- 

 ters in the upper Keys, sheltered 

 from the bay and cleansed with 

 Florida Current waters, are least 

 turbid. The middle Keys, at times, 

 are very turbid in response to move- 

 ment of bay waters over the reef 

 tract and into the Straits of Flor- 

 ida (Ball et al. 1967, Stockman 

 et al. 1967). Turbidity in the 



lower Keys and distal islands falls 



100 



