A REEVALUATION OF THE COMBINED EFFECTS OF 



TEMPERATURE AND SALINITY ON SURVIVAL AND GROWTH OF 



BIVALVE LARVAE USING RESPONSE SURFACE TECHNIQUES 



R. Gregory Lough^ 



ABSTRACT 



The combined effects of temperature and salinity on larval survival and growth of Crassostrea 

 virginica, Mercenaria mercenaria, and Mulinia lateralis as reported in the literature were critically 

 examined using response surface techniques. The late veliger larvae generally have a greater 

 tolerance to both temperature and salinity than the developing embryos. Each species shows its 

 own characteristic change in temperature-salinity tolerance as it develops and approaches the 

 range normally tolerated by the adults as it matures. Maximum growth of the veliger larvae 

 required higher temperatures and somewhat higher salinities than maximum survival. Dif- 

 ferences in temperature-salinity ranges estimated for maximum survival and growth were 

 significantly different for all three species. In each case growth showed a significant temperature- 

 salinity interaction. Response surface plots are given for early larval survival and late veliger 

 survival and growth. Inferences of tolerance studies are made to the fields of pollution and 

 aquaculture. 



Recent studies of the combined effects of tem- 

 perature and salinity on early development of 

 bivalve larvae have been done by Davis and 

 Calabrese (1964) for Crassostrea virginica and 

 Mercenaria mercenaria, Brenko and Calabrese 

 (1969) for Mytilus edulis, Calabrese (1969) for 

 Mulinia lateralis, Lough and Gonor (1971, 1973a, 

 b) for Adula californiensis , and Goodwin (1973) 

 for Panope generosa. However, only Lough and 

 Gonor (1973a, b) have critically examined the 

 effects of temperature and salinity on bivalve 

 larval life by multiple regression analyses and 

 the fitting of response surfaces to survival, 

 growth, and respiration of early and late stage 

 larvae. The use and evaluation of this response 

 surface technique in marine ecology has been 

 reviewed in detail by Alderdice (1972). This 

 technique not only facilitates the prediction of an 

 organism's response to a wide range of untested 

 conditions but also visually represents any change 

 in its response at various stages of development. 

 The experimental data from the above mentioned 

 species have been critically analyzed by response 

 surface techniques to reevaluate the combined 

 effects of temperature and salinity on larval 

 survival and growth. The results for Crassostrea 

 virginica, Mercenaria mercenaria, and Mulinia 

 lateralis are given in this paper. 



'School of Oceanography, Oregon State University, Corvallis, 

 OR 97331. 



METHODS 



The mathematical model used in the analyses 

 was of the form: 



y = 6o + 6i ^T) + 62 (S) + 63 {T"") + 64 {S^) 

 + b^{T X S) 



where Y = percentage survival or growth 

 60 = a constant 



T = linear effect of temperature 

 S = linear effect of salinity 

 T^ = quadratic effect of temperature 

 S^ = quadratic effect of salinity 

 T X S = interaction effect between tempera- 

 ture and salinity 



The coefficients in the model (6's) were esti- 

 mated by a stepwise multiple regression com- 

 puter program contained in the Oregon State 

 University Statistical Program Library. F-levels 

 were set equal to zero to enter and remove var- 

 iables. This allowed all variables to come into the 

 equation by a forward selection process, their 

 order of insertion determined by using the par- 

 tial correlation coefficient as a measure of their 

 importance. The contribution a variable makes 

 in reducing the variance of the equation can also 

 be considered by looking at the various values 

 given as the program proceeds. One of the more 

 useful is the square of the multiple correlation 



Manuscript accepted February 1974. 

 FISHERY BULLETIN: VOL. 73, NO, 1, 1975. 



86 



