JOHNSON EFFECTS OF TEMPERATURE AND SALINITY ON ACARTIA CAUFORNIE.\SIS EGOS 



D; 6). This delay, absent from the data on hatching 

 of summer eggs following an identical tempera- 

 ture increase, is evidence of a difference in the 

 character of dormancy in the two types of eggs. 



Resting egg mortality was low during the 11- 

 and 15-day incubation periods (Figui'es 5C, D). 

 Approximately 96'/c and SOf/c final hatch occurred 

 for eggs spawned at 13' and 9 C. respectively. The 

 somewhat lower viability of the 9 C spawned eggs 

 was also seen at hatching conditions of 17' and 21' 

 C (Figure 5A, B). Survival remained high (71'/f ) 

 for 9° C spawned eggs following 120 days incuba- 

 tion at 5" C (Figure 6). In comparison, the 13° C 

 spawned eggs had only 30% survival. This sub- 

 stantial difference in survival may not be impor- 

 tant, as opposite results were found for the hatch- 

 ing success of resting eggs from the preliminary 

 experiment under equivalent conditions (9° C 

 spawn = 45'7f ; 13° C spawn = 60''^ survival). The 

 implication is that resting egg survival is about 

 50'/f after a 4-mo dormant period. 



In most cases, hatching success at a given tem- 

 perature was similar for eggs of a given type 

 (summer or resting) spawned at different temper- 

 atures (Figures 5, 6). For example, 21 C spawned 

 eggs displayed little difference in hatching time or 

 success from 17°C spawned eggs at 21°, 17°. and 9° 

 C. The discrepancy in summer egg hatching times 

 and cumulative totals at 13° C was likely an ex- 

 perimental artifact since it was absent in the re- 

 sults of the preliminary expermient. Uye and 

 Fleminger (1976) similarly reported finding no 

 difference in hatching success at a given tempera- 

 ture for A. claust eggs spawned at 17.5" and 13.5° 

 C. 



A notable exception to this pattern occurred for 

 13° and 9° C spawned eggs which were incubated 

 at 21° and 17° C (Figure 5A, B). In both cases, the 

 9° C spawned eggs had a higher initial rate of 

 hatching than 13° C spawned eggs. By day 5, this 

 was reversed, and the rate for 13° C spawned eggs 

 exceeded that for 9° C spawned eggs. It is possible 

 that some of the 9° C spawned eggs had an en- 

 hanced metabolic rate relative to 13° C spawned 

 eggs, caused by cold acclimation (suggested by 

 Landry 1975b). Uye and Fleminger (1976) also 

 found evidence that cold-acclimated eggs of A. 

 tunsa, spawned at 6.5° C, tended to hatch more 

 quickly at temperatures below 12.5 C than eggs 

 spawned at 17.5° C. 



Long-term exposure to low temperature re- 

 sulted in abnormal development for some resting 

 eggs. This was only seen in 5-129c of the 9 C 



spawned eggs incubated at 9° or 5° C for 120 days. 

 Abnormalities of the newly hatched NI nauplii 

 ranged from mild to strong structural deforma- 

 tion. Some nauplii possessed an enlarged labrum 

 or fused appendages (e.g., second antennae and 

 mandible); some lacked appendages of one side of 

 the body. One nauplius had two severe constric- 

 tions which divided the body into three lobes. 

 Many of the abnormal nauplii were alive, though 

 weak, at the time of observation. Uye and 

 Fleminger (1976) also reported finding deformed 

 NI nauplii and postulated that osmotic stress from 

 abnormal salinities may have caused the deforma- 

 tions. In this case, however, deformation must 

 have resulted from long exposure to low tempera- 

 tures, since salinity was maintained at a favorable 

 concentration of 25%o. 



November Experiment 



Different hatching results were obtained using 

 eggs spawned by females acclimated at the 

 November field temperature of 12° C. Hatching 

 patterns (Figure 7) indicate that both nondormant 

 and resting eggs were produced concurrently in 

 the population. This is in contrast to production of 

 resting eggs only in the 13° and 9° C treatments of 

 females collected in October for the main experi- 

 ment (Figures 5, 6). The evidence for the presence 

 of both egg types is the two different hatching 

 rates which occurred at summer temperatures 

 (Figure 7). The initial hatching at 21° and 17° C 

 occurred within the first day, similar to summer 

 eggs at identical temperatures (Figure 5A, B). 



"> — ' — r 



10 15 



Incubation Time (days) 



Figure 7. — Hatching success of Acartia califorrnensis eggs 

 spawned by November-collected females at the field acclimation 

 temperature of 12" C. Hatchmg temperatures varied from 21° C 

 to 5" C; salinity was 25%o. Temperature increased to 21° C (de- 

 noted by vertical line) after variable periods of incubation below 

 17° C. 



575 



