JOHNSON: EFFECTS OF TEMPERATURE AND SALINITY ON AC.ARTIA CAUFORNIENSIS EGGS 



1972 



Figure 4. — Annual profile of bottom temperature 1° C) and sa- 

 linity (%»i at Station 39 in 1972. Values represent general range 

 of temperature-salinity experienced by resting eggs m surface 

 layer of sediments. December-May values from unpublished 

 data of H. F. Frolander (School of Oceanography, Oregon Stat* 

 Univ.. Corvallis. OR 97331). 



September (19°-22° C, 25-30%o) was followed by a 

 gradual decline to complete absence in late 

 November. Production of nondormant eggs re- 

 mained important throughout September, as evi- 

 denced by the large numbers of copepodites pres- 

 ent in the water column. However, copepodite 

 recruitment nearly ceased by the first week of 

 October, indicating that most reproduction was 

 likely in the form of resting eggs. Some nondor- 

 mant eggs were still produced, however, since a 

 small pulse of copepodites was seen in the last half 

 of October. Mean temperature had dropped to 

 13°- 15° C at the end of September when recruit- 

 ment began to fail. The population was gone by 

 December at a field temperature of 9°- 10° C. Salin- 

 ity remained high, relatively stable, and presum- 

 ably in a favorable range (25-30'U) during the 

 September-October decline and disappearance. 

 Salinity began to drop only in November when A. 

 californiensiswas essentially absent from the 

 water column. 



Resting Egg Production 



October Experiment (Preliminan.) 



Eggs collected on the third day of adult acclima- 

 tion to 21°, 17°, 13°, or 9°C had essentially similar 

 hatching rates and cumulative hatching success 

 at a given temperature to eggs collected on the 

 eighth day . The similarity in results indicates that 

 A. californiensis can shift from production of non- 



dormant eggs to production of resting eggs in only 

 1-2 days in response to a significant lowering of 

 water temperature. The absence of significant 

 changes in egg hatching time and viability with 

 increasing adult acclimation time demonstrates 

 that the eggs produced were not adversely affected 

 by the rapid change in water temperature (2-4 h) 

 at the beginning of the acclimation period. The 

 only effect observed was an initially lower fecun- 

 dity in those females which experienced the 

 largest temperature changes ( 16.8° C to 21°C or 9° 

 Cl. In these latter two cultures, fecundity in- 

 creased with acclimation time. 



October Experiment (Main) 



Hatching successes of eggs spawned over the 

 range of 9°-21° C give evidence that the type of egg 

 spawned is a function of ambient temperature 

 (Figures 5, 6). Experimental conditions and re- 

 sults are also summarized in Table 1. Females 

 which spawned at 21° and 17° C (typical midsum- 

 mer temperatures at Stations 29-45) produced 

 nondormant summer eggs that developed nor- 

 mally at 21° and 17° C (Figure 5A, B). Develop- 

 ment time was <36 h with nearly 100% of the eggs 

 hatching. Lower hatching temperatures (13°, 9°, 

 5° C), however, were found to arrest development 

 of summer eggs which then entered dormancy. 

 The incidence of dormancy increased with de- 

 creasing hatching temperature: eggs spawned at 

 17° C had a total hatching success of 71% at 13° C 

 compared with 35% at 9° C (Figure 5C, D) and 5% 

 at 5° C (Figure 6). Thus dormancy in summer 

 eggs is a response to low, unfavorable tempera- 

 tures and may occur independently of parental 

 influence. 



More than adequate time (Table 2) was allowed 

 in these experiments for "normal" hatching, given 

 the prediction from a Belehradek function for A . 

 tonsa (Zillioux and Gonzalez 1972) and the ob- 

 served development rates for A. claiisi (Landiy 

 1975b). A subsequent increase in water tempera- 

 ture to 21° C broke the dormancy of the summer 

 eggs previously incubated at 13° and 9 C (Figure 

 5C, D). Hatching resumed within a few hours at a 

 rate similar to that observed earlier at 17° and 21° 

 C (Figure 5A, B). 



Mortality of summer eggs spawned at 17° C was 

 low during the 1 1- and 15-day "holding" periods at 

 13° and 9° C (Figure 5C, D), evidenced by a final 

 hatching success of 90-96% after increase to21°C. 

 However, dormant 21° C summer eggs experi- 

 enced substantial mortality during the 15-day 



573 



