JOHNSON EFFKCTS OF TEMPERATIRE AND SALINITY ON ACAHTIA CAUFdRMEXSIS EGGS 



tively retained all copepodite stages. Tows were 

 oblique in a stepwise pattern from just above the 

 bottom to near surface at midchannel. A cali- 

 brated propeller flowmeter in the mouth of the net 

 was used to estimate the quantity of water filtered. 

 volumes filtered were typically 5-6 m*. Tempera- 

 ture measurements and salinity samples were 

 taken at the surface and just above the bottom at 

 each station. Salinities were later determined by 

 inductive salinometer in the laboratory. 



RESTING EGG PRODUCTION 



October Experiment 



Adult A. californicnsia were collected at Station 

 39 (Figure 1 ) on 9 October 1975, using a 239 ^m 

 mesh net towed slowly at 1-2 m depth. Surface 

 temperature and salinity were 14.9 C and 26.8"™., 

 respectively. Laboratory cultures were estab- 

 lished the same day by sorting 50 female and 25 

 male adults into each of eight 1,400 ml beakers 

 containing 1,200 ml of Millipore^-filtered water 

 (25"'i.i.i. Water temperature increased to room 

 temperature (16.8' C±0.3°) during this time. 

 Upon completion of sorting, all newly spawned 

 eggs were removed by screening and discarded. 

 Replicate cultures were then transferred to water 

 baths and maintained at 21", 17\ 13\ and 9" C 

 ( ±0.1°). Continuous overhead lighting (low level) 

 was used throughout the experiment. 



Adults were fed daily with a mixture of 

 Pseiidoisochrysis sp., Isochrysis galhana, and 

 Thalassiogira fluviatilis at a concentration of 

 approximately 200,000-250,000 cells • ml' 

 Phytoplankton cultures were maintained in log- 

 phase at 16.8 C. Viability of the algal species over 

 the temperature range of 9 -21 C was not deter- 

 mined but assumed to be unimportant in the ex- 

 perimental design since A. californiensis adults 

 were provided excess food daily. In addition, adult 

 mortality was moderately low (estimated at 

 ■20*5) during the acclimation and spawning 

 period with similar losses observed in all cultures. 

 Thus, selection of adults in response to tempera- 

 ture or food during the acclimation period was not 

 likely a factor in influencing the type of egg 

 spawned. 



After the third day of adult acclimation, ac- 

 cumulated eggs were removed by gentle screen- 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



ing. The eggs were used in a preliminary experi- 

 ment on hatching success which differed from the 

 main experiment in that fewer hatching tempera- 

 tures were tested for eggs produced at each accli- 

 mation temperature. 



The main experiment was established with eggs 

 collected on the eighth day of adult acclimation. 

 Maximum egg age ranged from 5 days at 9° C to 1 

 day at 21" C because of differences in egg develop- 

 ment rate as a function of temperature. Eggs from 

 replicate cultures at a given acclimation tempera- 

 ture were mixed together in a Petri dish for sorting 

 by pipette. Water temperature was maintained as 

 close as possible to acclimation temperature dur- 

 ing sorting. Depending on the number of eggs 

 available, 10-15 replicate batches of 50 eggs each 

 were placed in small 6 ml Petri dishes ( 1 cm depth, 

 3.5 cm in diameter) containing 4-5 ml of 

 Millipore-filtered water (25";...). Dish bottoms were 

 marked in a grid for ease in counting at 25 • with a 

 dissecting scope. Salinity changes caused by evap- 

 oration were prevented by floating the small 

 dishes in transparent, tightly capped 100 ml beak- 

 ers filled with 80 ml of water (also 25'Kh,). Two and 

 usually three or more replicate dishes of 50 eggs 

 were then placed in each of five water baths at 21", 

 17 , 13 , 9°, and 5° C, respectively. This procedure 

 was repeated for eggs produced at all four acclima- 

 tion temperatures C2V , 17', 13", 9°C), resulting in 

 an experimental design (Table 1 ) using over 2,500 

 eggs. 



Hatching success was determined daily by mak- 

 ing separate counts of eggs remaining and hatched 

 nauplii. Nauplii were captured and removed daily 

 with a pipette. Every 5th day, water was changed 

 by pipette with minimum disturbance to the re- 

 maining eggs. Unhatched eggs were maintained 

 at the experimental temperature well past the 

 time expected for normal hatching (Table 2) and 

 then transferred to a favorable temperature (21° 

 C) to determine subsequent hatching success. 



November Experiment 



Animals collected on 4 November 1975 at Sta- 

 tion 39 ( 12° C, 21%o) were used to repeat the exper- 

 iment at the prevailing field temperature and sa- 

 linity conditions. By this time, the field population 

 of A. californiensiswas greatly reduced and egg 

 production was assumed to be primarily resting 

 eggs. Females were kept at 12° C and 2 l%u during 

 transfer to the laboratory and subsequent cultur- 

 ing. Eggs were collected on the fourth day of 



569 



