FISHERY BULLETIN: VOL. 70, NO. 2 



may be expected to reflect these pigments ac- 

 cordingly. I have examined larvae of H. fulgens 

 which were generally brown but with green velar 

 margins and those of H. sorenseni, which, as 

 described above, were beige with yellowish velar 

 margins. Tissues of larval H. corrugata are 

 light yellow-green while velar fringes are a 

 darker shade of green. 



Color of the digestive gland in planktotrophic 

 prosobranch larvae has been shown to reflect 

 diet (Fretter and Montgomery, 1968). Since 

 HaUotis veliger larvae are lecithotrophic, color 

 of the digestive gland may have diagnostic value. 

 The maroon-colored digestive gland of H. soren- 

 seni veligers appears to be distinctive; I have 

 not observed other than green or brown in the 

 digestive glands of other haliotid veligers. 



Although development of larvae and growth 

 of settled juvenile H. sorenseni were more rapid 

 at higher temperatures, survival was reduced at 

 20°C. More advanced juveniles, reared initially 

 at 15-20°C, did not appear adversely aff"ected by 

 temperatures as high as 25 °C. Possibly thermal 

 tolerance limits are more restricted in larvae 

 and recently settled individuals. Certainly other 

 factors could have influenced success at higher 

 temperatures. Despite weekly changes of water, 

 bacterial, algal, and protozoan growth together 

 with a build up of metabolites and reduced oxy- 

 gen tensions in the relatively small volume of 

 water used in the thermal gradient study could 

 have influenced the results. 



Larval H. sorenseni were not successful at 10- 

 12°C. Water temperatures within the bathy- 

 metric range of the species may fall to 12° and 

 occasionally to 11°C (e.g., at depths of 130 ft 

 oflf Santa Catalina Island, T. Tutschulte, per- 

 sonal communication). Therefore the 10° or 

 12° C bathyisotherms may limit the depth to 

 which larvae of H. sorenseni may successfully 

 settle and grow. The results of the temperature 

 block study indicate the range 14-18°C may be 

 optimal for H. sorenseni larvae — an outcome not 

 unexpected in view of the prevailing conditions 

 in the natural environment from Pt. Conception 

 to central Baja California. 



Information on growth throughout the first 

 days of life is available for several species of 

 HaUotis. Ino (1952) reported that H. discus 



attained only 1.25-1.40 mm at 100 days and that 

 the first respiratory pore was not formed until 

 130 days. In contrast, Oba (1964) observed 

 rapid early development of H. diversicolor super- 

 texta. In that study, trochophores hatched at 

 only 6 hr, veligers developed within 11 hr and 

 settled by 2 days. The first respiratory pore 

 was formed as soon as 23 days after fertilization. 

 Interpolating from his growth curve, 100-day 

 juveniles ranged from 8 to 13 mm (Oba et al, 

 1968). In Ino's study, water temperatures de- 

 clined from 18° to 10°C through the course of 

 observations while Oba's work was carried out 

 during the summer and fall when temperatures 

 ranged between 20° and 28 °C. Whether the dif- 

 ferent development rates in these two species 

 reflect specific contrasts or thermal influences 

 is not clear. In another study (Kan-no and Ki- 

 kuchi, 1962), H. discus hannai was reared at 

 a relatively constant intermediate temperature 

 (19-20°C). This species also exhibited rapid 

 early development, settling in 3 days. Juveniles 

 reached 11 mm in length at 100 days and 26 mm 

 at 180 days. 



The rather extreme variability in growth rate 

 observed in H. sorenseni has also been found in 

 H. rufescens (Leighton, unpublished data). 

 Comparable variability is reflected in Oba's 

 growth curve for H. diversicolor supertexta. 

 DiflFerences in growth rate may reflect variation 

 in food availability. In the present study, care 

 was taken to provide uniform food distribution 

 and feeding conditions. Yet within a single 

 container, even within sampled subareas, a full 

 spectrum of size variation could be found. The 

 hypothesis may be advanced that gametogenic 

 inequalities (e.g., yolk allotment) may be in- 

 volved giving greater advantage to some indi- 

 viduals over others. Indeed, mortalities were 

 more common among the smaller and presuma- 

 bly less active members. 



Inherent variability in growth rate may be 

 expected in nature to be complicated by differ- 

 ential quality and availability of food. Multi- 

 modal size-frequency distributions obtained for 

 juvenile HaUotis populations in the field have 

 been concluded to reflect multiple spawnings and 

 recruitment waves (Leighton and Boolootian, 

 1963; Boolootian, Farmanfarmaian, and Giese, 



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