Estuarine 

 •ubftreai 



Upper Trinity Bay 

 Upper Eaat Bay 

 Lower Trinity Bay 

 Upper Galveston Bay 

 Lower Eaat Bay 

 Lower Galveston Bay 



Salinity (%») 



Range *— 



10 20 30 



_J I I J I I I L_ 



Seasonal occurrence 



Winter 



Scarce 



None 



Scarce 



Scarce 



None 



None 



Spring 



Many 

 None 

 None 

 None 



None 

 None 



Sujnmer 



Many 



Many 



Scarce 



Scarce 



None 



None 



Fall 



Many 

 Scarce 

 Scarce 

 Scarce 



None 

 None 



Figure 32.--Occurrence of Rangia cuneata in the Galveston estuary in relation to salinity, 1964. 



having considerable variation in percentage 

 composition of the sand, silt, and clay. Rangia 

 was not abundant, however, if the sand, silt, 

 and clay constituents exceeded 80, 30, and 65 

 percent, respectively, or if sand and clay 

 comprised less than 12 and 14 percent, re- 

 spectively, of the bottom sediment (fig, 33). 



Reliable quantitative data are difficult to 

 obtain with the dredge we used; a much im- 

 proved collecting device is needed if we are 

 to describe accurately the population density 

 of the many species of botton^ dwelling orga- 

 nisms. One such device (fig. 34), an under- 

 water "vacuunn cleaner" that removes intact 

 all of the animals and sedinnents from a known 

 area or volunne of bottonn, is being tested. ° 25 so 75 100 



Figure 33. — Distribution of Rangia cuneata in Galveston 

 Jack C, Parker, Acting Project Leader estuary during 1964 in relation to bottom types. 



F 



Figure 34. — New "vacuum cleaner" bottom sampler being tested. This device provides a 

 quantitative sample by removing all sediments and animals from 1/10 m.2 (1.08 ft.2) of 

 the bottom to a depth of 5 In. 



36 



