Ecophysiological studies on the ontogeny of euryplasticity in the caridean shrimp, Palaemonetes pugio (Hothuis) and modifications by zinc

Abstract

Larvae of the estuarine caridean shrimp Palaemonetes pugio (Holthuis) were reared from hatch through completion o f metamorphosis in 80 combinations o f salinity (3 to 31 o/oo ), temperature (20 to 35°C), and zinc (0.00 to 1.00 ppm Zn++). Response-surface methodology demonstrated that outside optimal salinity-temperature conditions (17 to 27 o/oo S and 20 to 27°C), viability of larvae was reduced by both the individual and interactive effects of salinity and temperature. Survival capacity of larvae and resistance adaptations to salinity and temperature were progressively reduced by increasing zinc concentrations. Response-surface analysis of the data suggested that the duration of total larval development o f P. pugio was least at salinities from 18 to 23 o/oo and at temperatures from 30 to 32°C. At both higher and lower salinity-temperature conditions and in increasing zinc concentrations, developmental rates were retarded. Increasing zinc concentrations reduced both survival and developmental rates of larvae more at suboptimal temperatures. Larval resistance to zinc toxicity was least at supraoptimal salinities. Changing patterns in several developmental processes, resistance adaptations, and several metabolic rate functions were analyzed by multiple regression analysis and response-surface methodology during the complete larval development of P. pugio reared from hatch through metamorphosis in 9 combinations of salinity (7-31 o/oo) and temperatures (20- 30°C) both with and without continual sublethal zinc exposure (0.25 ppm Zn++). The significant influence of salinity, resulting in more larval stages with an increase in salinity above approximately 20 o/oo, agrees with the species-habitat relationship seen within the genus Palaemonetes. At temperatures above 25°C, temperature increases masked any salinity effect and resulted in a reduction in the total number of larval stages. Zinc exposure did not alter the number of larval stages. ...