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Figure 2. — River discharge, precipitation, and hydro- 

 logical properties at station 1, Hillsborough River, 

 Fla., January 1964 to January 1965. (Open bars = sur- 

 face; solid bars = bottom.) 



titil III*' Diitkitfi 



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 D [:iDi[:k[li:tacnrki[lLfln 



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acvanci ^lilIJjlI 



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I F M t a I J « s 

 I9S4 SS 



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Figure 3. — River discharge, precipitation, and hydro- 

 logical properties at station 2, Alalia River, Fla., Jan- 

 uary 1964 to January 196.'). (Open bars = surface; solid 

 bars = bottom.) 



Salinity is a limiting factor in the distribution 

 of many marine and estuarine organisms, but 

 reliable data on the relation of estuarine organ- 

 isms to salinity are scarce (Gunter, 1961). The 

 unstable salinity at most stations was an ecologi- 

 cal barrier to stenohaUne and to some euryhaline 

 organisms. Conditions were suitable only to forms 

 that can exist over the entire salinity range from 

 fresh water to sea water. 



Since the favorable salinity range for the growtli 

 of Gymnodinium breve lies between 21 and 37 p.]).t. 

 (Rounsefell and Dragovich, 1966), sahnities at the 

 river stations were seldom favorable for its growth 



TEMPERATURE 



The annual temperature ranges during this 

 study were the observed tolerance ranges for 

 fishes (Springer and Woodburn, 1960) and in- 

 vertebrates (Dragovich and Kelly, 1964) in 

 Tampa Bay and for resident biota in Florida Bay 

 (Tabb and Manning, 1961). 



The water temperature varied from 12.8° to 

 32.4° C; monthly changes in all rivers and sta- 

 tions were similar (figs. 2-11). Temperatures 

 were high from April through September (highest 

 in June and July 1964), and low in December, 

 January, and February (lowest in Januar\' 1965). 



Temperature differences between surface and 

 bottom were less than 0.5° C in about 92 ])ercent 

 of the observations; twice they exceeded 1° C\ 

 Temperatures at the stations ^vith brackish water 

 were affected by displacement of water masses 

 tluring tidal oscillations. 



CHLOROPHYLL "a" 



Concentrations of chlorophyll "a" varied from 

 1.3 to 245.5 mg. per cubic meter. The highest 

 individual and mean values for the entire period 

 were at station 8 in the Peace River (fig. 9), 

 where mean surface and bottom concentrations 

 were 82.3 and 49.2 ing. per cubic meter. At other 

 stations, corresponding values varied from 3.9 to 



466 



U.S. FISH AND WILDLIFE SERVICE 



