Abalone aquaculture is dependent on cultured algae to induce larval settlement and as a food source for the early life stages of abalone until formulated feed or macroalgae such as Macrocystis sp., Porphyra sp. and Ulva sp. are introduced into the growout system. In the natural environment, abalone larvae settle on coralline red algae, which provide one of the strongest and most consistent settlement cues available for abalone larvae. However, propagation of coralline red algae is not practical commercially. Abalone farms in Japan successfully settle abalone larvae (Haliotis discus hannai) on the green alga Ulvella lens. U. lens also proved to be suitable to enhance settlement of cultured southern Australian abalone species (Haliotis laevigata, H. rubra). Most abalone farms in Australia are now growing U. lens for that purpose. U. lens is easy to culture, no specific facilities are needed and the alga can be grown on PVC settlement plates in commercial nursery tanks. However, U. lens has limited value as a feed for young postlarvae. Instead, cultured diatoms can be added after larvae successfully settle and start feeding. Juvenile abalone (>3 mm in shell length) can consume U. lens and grow rapidly on this alga. Diatom cultures and biofilms developing on settlement plates are not axenic and the role of bacteria in early postlarvae feeding is poorly understood. It has been suggested that bacteria may perform metabolic activities in the undeveloped gut of young postlarvae. At later stages of the nursery phase it becomes increasingly difficult to maintain adequate feed on the plates and this is still regarded as a significant bottleneck for the abalone aquaculture industry. Recent investigations have indicated that sporelings of macroalgae like Ulva sp. or diatoms that can provide more biomass may provide a suitable additional food source for juveniles (>3 mm in shell length).
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Vol. 25 • No. 1