from 5.2 to 8.4 milligrams per liter, changing with the hour of day and 

 season. Salinity is relatively uniform at 36 to 38 parts per thousand, and 

 pH values vary from 8.1 to 8.5, all of which is well within the optimal 

 range for coral reef development. The area undergoes an annual wet-dry 

 hydrological cycle, with rainfall highest during the summer and fall, and a 

 relatively dry season extending from about December through April. The air 

 temperatures and prevailing wind directions which accompany these weather 

 conditions exert some influence on the reef ecology. 



In summer, as is usual in tropical marine environments, and with winds 

 mostly from the southeast, air temperatures may climb to 35°C. Surface 

 water temperatures on the outer reefs then measure usually 30 to 31 °C, which 

 is close to optimal for reef-corals (Vaughan and Wells, 1943). In the winter 

 months, winds prevail from the east, northeast, and north, and frost m^ 

 reach the southern tip of continental Florida, resulting in an air temperature 

 in the Keys only slightly above freezing. These extremes are caused by cold 

 fronts with strong northerly winds. Due to the east-west orientation of the 

 Reef Tract and open passages in the lower Keys, wind-driven winter currents 

 may carry large masses of cold Florida Bay water to the outer reefs and 

 lower water temperature there to less than 20°C. This phenomenon may also 

 be aided by movements of the Loop Current (Marszalek, 1977). Ginsburg and 

 Shinn (1964) observed that reefs occur mainly opposite land where they are 

 less exposed to Florida Bay water. For this reason, reefs are least developed 

 in the widely spaced middle Keys, and the largest reefs are found in the 

 upper Keys, where they are protected from cold Bay water by landbarriers, 

 by their north-south orientation, and close proximity of the Gulf Stream, 

 Measurements of minimum water temperatures made by Vaughan (1918) over a 

 period of 20 years, were 15.6°C. at Fowey Rocks, 18.2°C at Carysfort Reef, 

 and 17.9°C off Key West. 



The seasonal drop in water temperature is the most severe natural factor 

 controlling coral reef development in Florida. Although a few species of 

 hermatypic corals endure colder water, most species die at about 16°C (Mayer, 

 1916), while exposure to about 18°C will block their growth (Mayer, 1914). 

 Although the situation may be different in certain IndoPacific reefs (Glynn, 

 1977), fluctuating water temperatures that remain below 24°C seem to inhibit 

 prominent coral reef development in the Caribbean Sea (Antonius, 1972). Dr. 

 Antonius, as well as other marine biologists have measured growth-rates of 

 several species of corals in Florida and areas of the Caribbean Sea (Antonius, 

 personal communications). In many cases, coral growth-rates in Florida were 

 found to be only about half or less the values found in central Caribbean 

 reefs. For example, an easily measured growth-rate is that of the staghorn 

 coral, Acropora cervicornis . It is about 10 cm per year in the Florida Reef 

 Tract, but in excess of 20 cm in reefs of the Virgin Islands as well as the 

 Barrier Reef of Belize, Central America (Robinson, personal communication, 

 1974). 



It appears, therefore, that Florida's coral reefs, including Looe Key, 

 could grow only about half as fast as central Caribbean reefs, and any damage 

 done to the coral framework can take twice as long to heal or regrow. 



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