Gunter and his associates (Gunter 

 1945; Gunter et al. 1964) conducted 

 early and extensive field studies es- 

 tablishing the range of salinity oc- 

 currences of fish and invertebrates 

 on the gulf coast. Laboratory stud- 

 ies determining salinity tolerance 

 ranges and optima and temperature- 

 salinity interactions for shrimp spe- 

 cies have been summarized by Zein- 

 Eldin and Griffith (1969) and Venka- 

 taramiah et al. (1974). Pearse and 

 Gunter (1957) showed that an ability 

 to tolerate salinity extremes through 

 one mechanism or another is an im- 

 portant characteristic of estuarine 

 organisms. They reported on early 

 indications that tolerance to low sa- 

 linities is enhanced by high concen- 

 trations of calcium in the water. 



The use of estuaries as nursery 

 grounds was established by Gunter 

 (1945) and supported by Sykes and 

 Finucane (1966), Tabb et al. (1962), 

 and many others. Gunter et al. 

 (1964) described the partitioning of 

 estuarine habitat among shrimp spe- 

 cies by salinity gradients. Gunter 

 (1945) was the first of many re- 

 searchers to point out that the spa- 

 tial distribution of organisms of 

 different sizes within species ap- 

 pears to follow the salinity gradient 

 in estuaries, with the smallest in- 

 dividuals in the lowest-salinity 

 areas. Reid and Hoese (1958) demon- 

 strated that factors other than sa- 

 linity may be responsible for the ob- 

 served distribution by size. 



Ray (1954), Carriker (1955), 

 Mackin (1956), Galtsoff (1964), Men- 

 zel et al. (1966), and Van Sickle et 

 al. (1976) discussed the effect of 

 lowered salinities on the enemies of 

 oysters. Gunter (1961) proposed that 

 mobile juvenile estuarine organisms, 

 like oysters, are protected from 

 stenohaline predators by estuarine 

 salinity gradients. 



Heald (1971) showed that large 

 quantities of organic material de- 

 rived from coastal swamp lands are 

 flushed into estuaries of Everglades 

 National Park, Florida. The impor- 

 tance of this material in estuarine 

 food chains was determined by Odum 

 (1971). 



Strong positive correlations 

 have been demonstrated between white 

 shrimp landings and annual rainfall 

 in Texas (Hildebrand and Gunter 

 1952; Gunter and Hildebrand 1954). 

 Chapman (1966) showed that, during 

 a seven-year period, average annual 

 commercial fishery harvests per unit 

 area in Texas estuaries were posi- 

 tively related to average gauged 

 freshwater inflows in all but one 

 estuary, the Mission-Aransas . Re- 

 sults of recent Gulf of Mexico stud- 

 ies utilizing correlation-regression 

 analyses will be discussed in the 

 next section. 



RECENT RESEARCH IN GULF OF MEXICO 

 ESTUARIES 



Diverse estuarine systems found 

 along the gulf coast from Florida to 

 Texas have similar problems as a re- 

 sult of changes in the quantity and 

 seasonal patterns of the freshwater 

 flow they receive. A brief descrip- 

 tion will be given of estuaries in 

 Florida, Louisiana, and Texas where 

 current research related to these 

 problems is being conducted. 



SOUTH FLORIDA 



Four characteristics of south 

 Florida's rainfall pattern that in- 

 fluence the pattern of runoff to 

 estuaries are: (1) moderately high 

 annual volume; (2) annual variation; 

 (3) seasonally variable distribution; 

 and (4) spatial variation. Average 



406 



