LEIGHTON: ABALONE MARICULTURE 



1986) and may involve yet unidentified media- 

 tors and environmental cues. Further insight 

 regarding use of GABA and other bioactive sub- 

 stances to prompt settlement and metamorpho- 

 sis may be gained from the analysis and discus- 

 sion by Pawlik (1988). 



The behavior of larvae at settlement is critical 

 to subsequent survival. In the presence of many 

 elements common to the native environment of 

 abalone, including microfloral colonies (diatoms, 

 bacterial films, etc.), biliprotein-containing 

 crustose red algae and cyanobacteria (Morse et 

 al. 1984) and even "mucous trails" of conspecific 

 juveniles (Seki and Kan-no 1981; Leighton 1985; 

 Slattery 1987), advanced larvae of H. riifescens 

 and other species examined exhibit a typical 

 swimming behavior consisting of a series of land- 

 ings and takeoffs as if testing the substrate prior 

 to settlement. Surface acceptance is independent 

 of orientation; settlement may be on container 

 sides, bottom, or even on the undersides of in- 

 cluded substrates. In contrast, in the presence of 

 GABA, larvae often settle promptly (usually 

 within 2 hours at 10 •" M), but almost exclu- 

 sively on container bottoms. In the hatchery set- 

 ting, the tank bottom rapidly becomes a hostile 

 environment and larvae settled there soon suc- 

 cumb to bacterial overgrowth. Using diatom 

 films and other natural substrates, dispersal is 

 optimized and subsequent settling and meta- 

 morphosis are normal (Leighton 1977, 1985). 

 GABA is not used routinely in commercial facili- 

 ties for the reasons cited above. 



In California abalone hatcheries, larvae at 

 competence are admitted to tanks appropriately 

 prepared for settling and metamorphosis con- 

 taining partially cleared diatom coatings 

 (Leighton 1977), other microflora, or traces of 

 mucus and associated substances left by former 

 conspecific occupants (Leighton 1985, 1987; Slat- 

 tery 1987). In the early stages of red abalone 

 mariculture (Leighton, pers. obs. 1970-75) 

 crustose coraUine red algae {Lithothamnion and 

 related forms) were cultured within special post- 

 larval culture tanks. Settlement on coraUine sur- 

 faces was often intense, and subsequent survival 

 and growi;h of postlarvae was excellent. How- 

 ever, juveniles larger than 5 mm derived de- 

 creased nutriment from the coralline-benthic 

 diatom substrate, necessitating their transfer to 

 tanks precolonized by diverse microflora and to 

 which macroalgae were supplied as foods. This 

 observation is in confirmation of results (Leigh- 

 ton 1968: table XXX) showing reduced nutri- 

 tional benefit of crustose coralline algal sub- 



strates for juvenile H. nifescens. It was also 

 found in early hatchery operations that larval 

 settling and postlarval success were greatly im- 

 proved in fiberglass tanks which had recently 

 held conspecific juveniles and adults (Leighton, 

 pers. obs. 1971). More recently, Japanese biolo- 

 gists have found a similar benefit for larval 

 recruitment to exist in H. discus hannai (Seki 

 and Kan-no 1981). 



As noted earlier, postlarval attrition still lim- 

 its the efficiency of abalone mariculture, al- 

 though claims to the contrary appear in the liter- 

 ature (e.g.. Hooker and Morse 1985). Losses of 

 60-80% of postlarvae are commonly experienced 

 during the second to sixth weeks following fertil- 

 ization (Leighton 1985). While microbial patho- 

 gens have not often been demonstrated, a por- 

 tion of the postlarval attrition may be due to 

 disease. Mortahties may be reduced by provid- 

 ing intensive care to small-scale cultures for 

 which antibiotic prophylaxis or other procedures 

 are followed to minimize epizootic complications. 

 A parasitic protozoan found especially lethal to 

 juveniles younger than 190 days, but not in- 

 jurious to more mature abalone, was isolated 

 from an abalone hatchery in British Columbia 

 (Bower 1987). Since many potentially deleter- 

 ious organisms (e.g.. Vibrio spp.) appear to 

 thrive in decomposing organic matter, the well- 

 managed hatchery is not Hkely to experience 

 epidemic outbreaks of bacterial and protozoan 

 diseases. 



Regardless of the approach, a major portion of 

 the postmetamorphic young eventually succumb 

 before passing early juvenile stages (Leighton 

 1985). In practice, the high fecundity typical of 

 mature female abalone acts in compensation for 

 the large losses, and spawnings of small numbers 

 of broodstock supply commonly several million 

 larvae on each occasion. 



The U.S. species of abalones most produced 

 by mariculture, the red and the green, differ 

 markedly in their requirements of nutrition as 

 well as temperature (Leighton 1987). Kelps com- 

 monly used as foods for abalone in California 

 mariculture are Macrocystis pyrifera and 

 Egregia menzesii. The former is a valuable food 

 for young red abalone, but a relatively poor diet 

 for green abalone (Table 1). Egregia is effec- 

 tively utilized by both species and is the diet of 

 choice for culture of green abalone (Leighton et 

 al. 1981). Laminaria farlowii , common in south- 

 ern California, is also a productive diet, espe- 

 cially for green abalone. Mixed algal diets yield 

 superior growth (Leighton 1968, 1977). 



699 



