GALVESTON ESTUARY 



KM. 

 FROM 

 ZONE RIVER MAY JUN JUL AUG SEP OCT NOV. DEC. 



Figure 22. — Period of influence of May 1963 Trinity River flow on salinity of Galveston estuary. 



July, the high did not occur in upper Trinity- 

 Bay until November. 



The configuration of the Galveston estuary 

 provides a natural "trapping" effect so that 

 relatively small volumes of fresh water exert 

 considerable influence for months. Should the 

 constriction between the upper and lower bays 

 become more severe, however, salinity in the 

 upper bays would probably remain low for 

 longer periods. 



Species Diversity 



The Galveston estuary provides a typical' 

 example of increasing species diversity at 

 higher salinities. Of more than 150 species 

 of fish, crab, and shrimp collected in small 

 trawls, 74 were caught in the higher salinities 

 (20 to 30 p.p.t.) of lower Galveston Bay, 59 in 

 upper Galveston Bay, and only 45 in the rela- 

 tively low-salinity waters near the river mouth. 

 Although more species were caught in waters 

 of high salinity, the greatest numbers of indi- 

 viduals (all species combined) were taken in 

 the lower salinity waters of the upper estuary. 

 The average size of animals of each species 

 was smaller in the upper estuary than in the 

 lower bay. The relation of temperature to 

 species diversity was also typical of Gulf 

 estuaries. The collection of more species 

 in water where temperature varied between 

 10° and 30 C. than at other temperatures 

 indicates that many species may be sensi- 

 tive to high temperatures in summer as 

 well as to low temperatures in the winter 

 (fig. 23). 



60 



_, 20 



BOTTOM SALINITY (%.) 



g 40 - 



BOTTOM TEMPERATURE ( 'C I 



10 



20 



40 



Figure 23. — Diversity of species of fish, 

 crab, and shrimp In relation to tempera- 

 ture and salinity In the Galveston estuary. 



23 



