LEIGHTON: EARLY GROWTH OF THE ABALONE 



Figure 1. — Three-day veliger larva of Haliotis sorenseni. 

 (Shell diameter, 270 jj.) a. shell, b. digestive gland, 

 c. velum, d. eye spot, e. incipient cephalic tentacle, f. foot, 

 g. operculum. 



digestive gland was maroon. Swimming of ve- 

 ligers at this stage carried them throughout the 

 water column. 



Settlement occurred at 9-10 days at 15°C. 

 Velar dystrophy, with loss of ciliated fringes, 

 took place gradually, and larvae retained the 

 ability to swim if dislodged for several days 

 after initial settlement. 



INFLUENCE OF TEMPERATURE ON 

 DEVELOPMENT RATE 



Larvae confined to 100-ml beakers in the 

 thermal gradient block appeared, except for the 



temperature efl^ects to be described, to be normal 

 in appearance and behavior and were similar 

 to larvae maintained in liter beakers at 15-17 °C. 

 Development was most rapid at higher temper- 

 atures; some individuals settled as early as the 

 7th day at 20°C and the 8th day at 18°C. By 

 the 15th day almost all larvae at the two highest 

 temperatures had settled, yet none had settled 

 at 10°C (Table 1, Figures 2 and 3). By the 

 25th day most larvae at 10°C had succumbed, 

 having progressed only to the late veliger stage. 

 Settling rate varied within groups, and even at 

 18 °C approximately 5% did not settle. 



Observations at the end of the 36-day exper- 

 iment revealed that survival was best at 16° 

 and 18°C, somewhat less at 20° and least at 14° 

 and below. Larvae maintained at 10°C did not 

 survive beyond 25 days and most of those at 12° 

 failed at 25 to 30 days. Size attained by settled 

 juveniles corresponded with survival; at 36 days 

 shell lengths as great as 1.2 mm were attained 

 at 18°C, about 1.0 mm at 20° and 16°C, and 

 only 0.6 mm at 12° and 14°C. 



GROWTH OF JUVENILE H. SORENSENI 



Approximately 100 settled juveniles were ob- 

 tained from the larvae reared in liter Pyrex 

 beakers at 15-17°C. These individuals were 

 carefully dislodged by a jetting stream of water 

 and teasing needle and transferred to larger con- 

 tainers to observe growth and behavior under 

 a variety of food and water flow situations. 

 Food quality and quantity was not limited to in- 

 sure maximum growth, hence a wide variety of 

 food organisms was provided (pennate diatoms 

 and filamentous red, green, and brown algae) . 



Table 1. — Number of Haliotis sorenseni larvae surviving and settled at 15 days in thermal gradient experiment. 



375 



