Key West St Petersburg Cedar Key Pen&ocola 



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30 



25 



20 



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 I? 15 



10 



90 



80 



H70 I 



60 -n 



50 



- 40 



Figure 3. Average monthly temperatures in Florida, 1965 (McNulty et al . 1972), 



and occasionally reduced salin- 

 of which stress the local shal- 



is thought that 

 type of water 

 the relatively 



turbulence 



ities, all 



low water communities. It 



the rapid influx of this 



from Florida Bay through 



open passages of the central Keys, when 



pushed by strong northwesterly winter 



winds, is the major factor in the reduced 



abundance of coral reefs in the central 



Keys (Marszalek et al. 1977). 



Tides are typically about 0.75 m (2.5 

 ft) at the Miami harbor mouth. This range 

 is reduced to 0.5 m (1.6 ft) in the embay- 

 ments such as South Biscayne Bay and to 

 0.3 m (1 ft) in restricted embayments like 

 Card Sound (Van de Kreeke 1976). The mean 

 range decreases to the south and is 0.4 m 

 (1.3 ft) at Key West Harbor. Tidal heights 

 and velocities are extremely complex in 

 south Florida as the Atlantic tides are 

 semidiurnal, the gulf tides tend to be di- 

 urnal, and much of this region is between 

 these two regimes. Neither tidal regime 

 is particularly strong, however, and winds 

 frequently overcome the predicted tides. 

 These factors, coupled with the baffling 

 effects of mudbanks, channels, and keys, 

 create an exceedingly complex tidal circu- 

 lation. 



1.3 GEOLOGIC ENVIRONMENT 



The south Florida mainland is low- 

 lying limestone rock known as Miami lime- 

 stone. For descriptive purposes the region 

 can be broken into four sections: the 

 south peninsular mainland (including the 

 Everglades), the sedimentary barrier 

 islands, the Florida Keys and reef tract, 

 and Florida Bay. 



The sedimentary barrier islands of 

 north Biscayne Bay, Miami Beach, Virginia 

 Key, and Key Biscayne are unique for the 

 area because they are composed largely of 

 quartz sand. The islands are the southern 

 terminus of the longshore transport of 

 sand that moves down the east coast and 

 ultimately out to sea south of Key Bis- 

 cayne. All other sediments of the region 

 are primarily biogenic carbonate. 



The Florida Keys are a narrow chain 

 of islands extending from tiny Soldier 

 Key, just south of Key Biscayne, in first 

 a southerly and then westerly arc 260 km 

 (163 mi) to Key West and ultimately to the 

 Marquesas and the Dry Tortugas some 110 km 

 (69 mi) further west. The upper keys, 

 from Big Pine northward, are composed of 



