LEIGHTON: INFLUENCE OF TEMPERATURE ON ABALONES 



rufescens (near 19°C) reached the early (preeye 

 spot) operculate stage, H. corrugata (near 23°C) 

 had formed eyespots and cephahc tentacle buds, 

 and H. fulgens (near 25°C) had become mid- 

 cephalic tentacle operculates. In the latter, set- 

 tling was observed as early as 3 days after fertili- 

 zation. 



OBSERVATIONS ON 

 TROCHOPHORE LARVAE 



When swimming trochophore larvae rather 

 than developing eggs were introduced to the 

 thermal gradient system, survival was improved. 

 In experiments initiated with fertilized eggs, sur- 

 vival beyond 3 days in the 20-ml tubes was low 

 despite routine addition of dihydrostreptomycin 

 sulfate and sulfanilamide (to final concentration, 

 10 ppm). Substances within the periviteliine space 

 (including excess sperm) are liberated at rupture 

 of the albumen membrane, frequently promoting 

 fouling. Temperature block studies in which 

 trochophore or veliger larvae were freed of con- 

 taminants by repeated transfer and then ad- 

 mitted to the tubes showed reduced mortality. 



Haliotis rufescens larvae settled approximately 

 4 days after fertilization (18°C). However, after 3 

 wk in the temperature block, only those groups 

 between 14° and 18°C had reached advanced post- 

 larval stages (Figure 4). Settling occurred in some 

 H. corrugata larvae within 3.5 days, but postlar- 

 vae did not survive (22°-23°C). Most rapid growth 

 and best survival in H. corrugata was at 21°-22°C; 

 the circular-shell postlarval stage was reached in 

 17 days (Figure 5). Settlement began in larvae of 

 H. fulgens at 25.5°C in slightly less than 3 days, 

 but again, subsequent success was poor. Those at 

 22°-23°C, however, settled by the fourth day and 

 progressed to the circular-shell stage in 15 days 

 (Figure 6). There was a close correspondence of 

 curves for development rate vs. temperature ob- 

 tained with progeny from different spawnings and 

 parentage. Optima described graphically for each 

 species varied within only 1°C for H. corrugata, 

 1.5°C for H. fulgens, and 2°C for H. rufescens. 



Larvae introduced to a thermal gradient as 

 operculate veligers exhibited tolerance to a 

 broader temperature range. Subsequent de- 

 velopment rate was, however, slowed. The general 

 retardation may be a shock response to environ- 

 mental change. The greatly reduced volume pro- 

 vided in the 20-ml tubes and the totally darkened 

 conditions in the temperature block contrast with 



Circular- 

 Shelled 



Mid Asymmetric — 



Eorly 

 Asymmetric 



Crawling 

 (Settling) 



Branched 

 Cephalic Tentacle 



Mid Cephalic 

 Tentocle 



Incipient 

 Cepholic Tentacle 



Operculote 

 Veliger 



Inf late-shell 

 Veliger 



Cap-shell 

 Veliger 



Trochophore 

 Larva 



10 15 20 25 



TEMPERATURE (°C) 



30 



Figure 4. — Development of larvae of Haliotis rufescens at a 

 series of temperatures when introduced to the thermal gradient 

 as trochophores. 



Circular  

 Shelled 



Mid Asymmetric - 



Early 

 Asymmetric 



Crawling 

 (Settling) 



Branched 

 Cephalic Tentacle 



Mid Cephalic 

 Tentacle 



Incipient 

 Cephalic Tentacle 



Operculate 

 Veliger 



Inflote-shell 

 Veliger 



Cop- shell 

 Veliger 



Trochophore 

 Larva 



15 20 



TEMPERATURE CO 



30 



Figure 5. — Stages attained by larvae of Haliotis corrugata over 

 a period of 17 days. Larvae were placed in the thermal gradient 

 at the trochophore stage. 



the 10-liter volume and illumination in the plastic 

 rearing containers. In an experiment illustrating 

 the point, H. corrugata eggs, trochophores and 

 operculate veligers were placed in the gradient for 

 5 days in each case. At 20°-22°C, eggs developed 

 rapidly and early postlarval stages reached in 5 

 days. However, operculate veligers had not yet 

 reached the crawling stage at an age of 7 days 

 (Figure 7). 



In temperature block experiments, survival 

 through settling usually ranged between 50 and 



1141 



