These measurements are providing field infor- 

 mation for the design of laboratory experiments 

 to determine whether temperature differentials 

 between water and substrate induce burrowing 

 in shrimp. 



In February, two additional thermistors were 

 installed to compare the temperature regime 

 of a very shallow peripheral inlet with that 

 of the lagoon proper. As anticipated, the 

 temperature fluctuations were considerably 

 wider in the peripheral water and substrate 

 than in the 6-ft.-deep water and its sub- 

 strate (fig. 38). Furthermore, temperature 

 differences between the shallow water and its 

 substrate were much greater than those in 

 the deeper location. 



These temperature data have also indicated 

 that the peripheral marsh during early spring 

 is consistently warmer than the 6-ft-deep 

 environment. Analysis of results for March 

 and the first half of April indicates that 91 

 percent of the observed temperatures (bottom 

 water and substrate) in the lagoon proper 

 were lower than or equal to those at the 

 shallow inlet. Weekly means for the two 

 locations differed by 2° to 5° C. (3.6° to 

 9.0° F.). Differences were frequently marked, 

 reaching 14° C. (13° vs. 27° C.) on one occa- 

 sion. (These tennperatures correspond to 2 5.2°, 

 55.4°, and 80.6° F., respectively.) 



These temperature characteristics further 

 support our consideration of the shallow 

 peripheral area as a discrete ecological zone 

 to be distinguished from the main body of the 

 estuary. In view of the marked influence of 

 temperature on the growth of young shrimp 

 (as well as other organisms), it is possible 

 that the temperature characteristics of the 

 bay's very shallow peripheral zone, which 

 the young shrimp first inhabit, may have an 

 important bearing on estuarine productivity 

 in the spring. The major annual influx of 

 brown shrimp postlarv"ae reached Galveston 



Figure 38. — Weekly temperature ranges and means in two 

 estuarine situations — shallow peripheral inlet and lagoon 

 proper — of East Lagoon, 1965. 



Bay during this early spring period, accord- 

 ing to the records of K. N. Baxter (Shrimp 

 Dynamics Program). 



From late April through June, there were 

 less striking differences between weeklymean 

 temperatures of the two situations and smaller 

 ranges overall. Continued observations will 

 provide data on summer temperature ex- 

 tremes and rates of change. We need this 

 information as background for the design and 

 evaluation of laboratory studies of how and 

 why shrimp respond to temperature. 



David V. Aldrich, Project Leader 



SHRIMP METABOLISM 



The metabolism project is concerned with 

 differences in physiology between the com- 

 mercially important brown and white shrimp. 

 Although several of the studies discussed 

 here concern growth, they began before the 

 growth and metabolism projects were sub- 

 divided and as a result were conducted jointly 

 by the two projects. 



Postlarvae of both species enter the bays 

 where salinities and temperatures may fluc- 

 tuate widely. In the northwestern Gulf, most 

 postlarvae of brown shrimp enter the bays 

 in the spring; smaller numbers arrive through- 

 out the summer. White shrimp postlarvae, 

 however, reach the bays during late spring 

 and summer. Thus, the postlarvae of the two 

 species are exposed to sonnewhat different 

 conditions during the period of active growth. 



A previous study compared the effects of 

 salinity and temperature upon the growth of 

 spring brown and summer white shrimp post- 

 larvae. The postlarvae of brown shrimp ap- 

 parently withstood low temperatures (52° F.) 

 far better than did the white postlarvae, where- 

 as at 90° F. the white shrimp survived and 

 grew slightly better than the brown shrimp. 

 The spring population of brown shrimp post- 

 larvae, however, had been accustomed to 

 cooler temperatures than the late- summer 

 white shrimp. To determine whether this 

 difference in temperature tolerance was re- 

 lated to species rather than to temperature 

 history alone, we studied postlarval brown 

 and white shrimp collected at the same time 

 (June) and, therefore, with the same tempera- 

 ture experience. Postlarvae of brown shrimp 

 again survived better than white shrimp at the 

 lowest test temperature (59° F.), and the white 

 shrimp survived somewhat better at the highest 

 test temperature (92.5° F.) (table 10). There 

 was a greater effect of warm temperature upon 

 growth rate of postlarval white shrimp than 

 upon growth rate of brown shrimp (fig. 39). 

 Postlarvae of white shrimp held 30 days at 

 92.5° F. were 8 mm. (0.31 in.) longer and 

 twice the weight of those held at 77°, but at 

 the end of the experiment brown postlarvae 



41 



