EFFECTS OF TEMPERATURE AND SALINITY ON 



LARVAL DEVELOPMENT OF GRASS SHRIMP, 



PALAEMONETES VULGARIS (DECAPODA, CARIDEA)" 



Paul A. Sandifer* 



ABSTRACT 



Larvae of Palaemonetes vulgaris were reared in the laboratory in a factorial experiment 

 employing three temperatures (20°, 25°, and 30°C) and six salinities (5, 10, 15, 20, 25, 

 and 30^!^^). Temperature and salinity exerted significant effects at the 1% level on sur- 

 vival of larvae through metamorphosis. The temperature-salinity interaction was also 

 significant, but at the 5% level. Lowest survival occurred in 5%,; at all temperatures. 

 In higher salinities, survival at 20° and 25°C was similar (>60%) but was significantly 

 less at 30°C in most salinities. Temperature and salinity also influenced the rate of 

 larval development. Development at 20 °C required nearly twice the time as that at 25° 

 and 30°C, but a retarding influence of salinity was slight and evident only at low salinities 

 (5 and lO^r) . Considerable variation in the number of larval instars was observed among 

 animals which survived to the postlarval stage. Metamorphosis occurred as early as the 

 fifth molt and as late as the twelfth. Salinity and temperature-salinity interaction had 

 no detectable influence on the number of instars, but the effect of temperature was sig- 

 nificant at the 1% level. Larvae reared at 25 °C passed through fewer molts prior to 

 metamorphosis than did those reared at 20° and 30°C. Comparing survival, rate of 

 development and number of instars, optimal conditions for larval development occurred 

 at a moderate temperature of about- 25° C over a wide range of salinity (10 to 30^o). 



The grass shrimp, Palaemonetes vulgaris (Say) , 

 ranges at least from Barnstable County, Mass., 

 to Cameron County, Tex., (Williams, 1965) and 

 is one of the most abundant estuarine decapods in 

 this range. In the laboratory, Nagabhushanam 

 (1961) found the species to be nearly euryhaline, 

 tolerating salinities from 3 to 35%f. More re- 

 cently, Bowler and Seidenberg (1971) found P. 

 vulgaris to be less tolerant of low salinities 

 (^3^f) but more tolerant of high salinities (36 

 and 40%c) than its congener, P. pugio. In the 



' Contribution No. 511 from the Virginia Institute of 

 Marine Science, Gloucester Point, Va. 



' This study was supported in part by the Sea Grant 

 Program of the Virginia Institute of Marine Science, 

 under contract GH67 from the National Oceanic and 

 Atmospheric Administration, U.S. Department of Com- 

 merce. This paper is based on part of a dissertation 

 to be presented to the Department of Marine Science, 

 University of Virginia, in partial fulfillment of the re- 

 quirements for the Doctor of Philosophy degree. 



^ South Carolina Marine Research Laboratory 217 Ft. 

 Johnson Road, P.O. Box 12559, Charleston. SC 29412. 



Manuscript accepted May 1972. 



FISHERY BULLETIN: VOL. 71, NO. 1, 1973. 



York River, Va., these authors found that the 

 percentage of the Palaemonetes population made 

 up by P. vulgaris decreased markedly with de- 

 creasing salinity, and in North Carolina, Knowl- 

 ton and Williams (1970) found P. vulgaris only 

 in waters of 15 to 35^f salinity. 



Only Knowlton (1965, 1970) has studied the 

 effects of temperature and salinity on P. vulgaris 

 larvae, and his results were limited by the small 

 number of experimental animals he used. The 

 objectives of the present study were to determine 

 the effects of temperature and salinity on sur- 

 vival and development of P. vulgaris larvae 

 reared through metamorphosis in the laboratory. 



MATERIALS AND METHODS 



The experimental design was a 3 X 6 factorial 

 using temperatures of 20°, 25°, and 30°C and 

 salinities of 5, 10, 15, 20, 25, and 30^^. Test 

 media were prepared by diluting seawater with 



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