82 A BIOLOGY OF CRUSTACEA 



vented by the combined effects of low temperature and low salinity, 

 for the shrimp can only withstand reduced salinities when the water 

 is reasonably warm. The breeding season in the estuary is only long 

 enough to allow the production of a single brood, but in the 

 Channel the season allows the production of two broods. Females 

 in the estuary do not produce a brood until their third year, while 

 those in the Channel produce a brood in their second year and two 

 broods in each of their third and fourth years. The more exacting 

 conditions of life in the estuary thus influence the reproductive 

 cycle in two ways. The breeding season is shortened and the onset 

 of maturity is delayed. 



The three examples of annual cycles show how each species 

 has its own particular breeding season and how each is modified 

 by variations in the environment. In Daphnia the availability of 

 algae and the density of the population are important; in 

 Sphaeroma the cycle is influenced greatly by the temperature in 

 spring, while in Crangon the combined effects of temperature and 

 salinity reduce breeding activity in estuaries. 



LITERATURE 



Barnes, H., & Powell, H. T. (1953). The growth of Balanus 

 balanoides (L.) and B. crenatus Brug. under varying conditions 

 of submersion. /. mar. Biol. Ass. U.K. 32: 107-127. 



Berg, K. (1934). Cyclic reproduction, sex determination and depres- 

 sion in the Cladocera. Biol. Rev. 9: 139-174. 



Carlisle, D. B. (1957). On the hormonal inhibition of moulting in 

 decapod Crustacea. II. The terminal anecdysis in Crabs. 

 /. mar. Biol. Ass. U.K. 36: 291-307. 



Costlow, J. D., & Bookhout, C. G. (1957). Body growth versus shell 

 growth in Balanus improvisus. Biol. Bull., Wood's Hole 113: 

 224-232^ 



Crisp, D. J., & Stubbings, H. G. (1957)- The orientation of barnacles 

 to water currents. /. anim. Ecol. 26: 179-196. 



Green, J. (1956). Growth, size and reproduction in Daphnia 

 (Crustacea: Cladocera). Proc. zool. Soc. Lond. 126: 173-204. 



Gurney, R. (1942). Larvae of decapod Crustacea. London, Ray 

 Society, pp. 1-306. 



