LOUGH: TEMPERATURE-SALINITY EFFECTS ON BIVALVE LARVAE 

 40n 



30 



a: 



< 



20 



lO- 



10 



20 

 SALIN I TY (%. 



30 



40 



Figure 5. — Response surface estimation of percent survival 

 of Mercenaria mercenaria veliger larvae after 10 days of 

 development at experimental temperature and salinity combi- 

 nations given in Davis and Calabrese (1964). 



Late larval survival after 10 days of rearing 

 at the experimental conditions indicated that 

 the linear and quadratic effects of salinity and 

 the interacting effect of temperature and salinity 



40 



30 



3 



< 



20 • 



lO- 



20 

 SALIN I TY (%„ 



30 



40 



Figure 6. — Response surface estimation of percent growth of 

 Mercenaria mercenaria veliger larvae after 10 days of 

 development at experimental temperature and salinity com- 

 binations given in Davis and Calabrese (1964). 



were the more important factors affecting sur- 

 vival. Maximum survival of these 12-day-old 

 larvae (80% survival contour) was estimated to 

 occur between temperatures and salinities of 

 19° and 29.5°C and 21 and 29%o (Figure 5). 

 Although the late larvae had a much narrower 

 temperature tolerance than the developing em- 

 bryos, the late larvae showed a significantly 

 greater tolerance to low salinity. This difference 

 in tolerance of these two life stages was further 

 substantiated by the fact that there was a sig- 

 nificant difference (1% level) between the 2- and 

 10-day survival polynomials. 



Growth of the larvae during the 10-day ex- 

 perimental period was most affected by the inter- 

 acting effect of temperature and salinity and 

 by the linear and quadratic effects of tempera- 

 ture, and the linear effect of salinity. Maximum 

 growth (80% contour) was estimated to occur at 

 temperatures and salinities between 22.5° and 

 36.5°C and 21.5 and 30o/oo (Figure 6). There was 

 a significant difference (1% level) between the 

 polynomials estimated for 10-day survival and 

 growth indicating that the higher tempera- 

 tures and salinities required for optimum growth 

 are significantly different than those conditions 

 estimated for optimum survival. Larval survival 

 and growth estimated by these techniques above 

 the experimental temperature and salinity of 

 32.5°C and 27.0%o are questionable. Higher 

 temperature and salinity levels need to be added 

 to the experimental design to more carefully 

 define the response surface. 



The combined 10-day survival and growth 

 analysis indicated that they were affected by all 

 of the variables of temperature and salinity, but 

 by salinity more than by temperature. Optimum 

 temperature and salinity conditions (80% contour) 

 for maximizing both larval survival and growth 

 to 12 days was estimated at 21.5° to 33°C and 

 22 to 31%o. 



Mulinia lateralis 



Six levels each of temperature and salinity 

 were used to investigate the tolerances of early 

 and late development of this species by Calabrese 

 (1969) in the same manner as used for the other 

 species. 



Survival of the early embryos for 2 days under 

 the experimental conditions was affected by all 

 the variables except the interacting effect of 



89 



