Settlement, early growth and survival of Haliotis rubra in response to different algal species

Five diatom species were isolated from settlement plates at Southern Ocean Mariculture, Victoria, Australia ( Navicula sp., Navicula jeffreyi, Cylindrotheca closterium, Cocconeis sp., Amphora sp.) and tested in settlement experiments with Haliotis rubra larvae. Settlement was very low on single species diatom films and varied between 1%-6%. Depending on the species combination larvae preferred to settle on films with mixed diatom species than single species films. The highest settlement was achieved with a mixed film of Navicula sp. and Amphora sp. Five and ten-day-old germlings of Sporolithon durum induced settlement of the abalone Haliotis rubra. However, the settlement rate was significantly lower on germlings than on the whole thallus of the alga. Germlings inoculated with the diatom Navicula sp. induced higher settlement than films of the diatom species alone. High settlement of up to 52% was also achieved with germlings of the green alga Ulvella lens. Settlement was reduced on U. lens squares inoculated with the diatom Navicula sp. but higher than on films of the diatom alone. The settlement rate was higher if plates with U. lens were previously grazed by juvenile abalone. Post-larval growth rates were higher on monospecific diatom films than on U. lens or on S. durum. The best growth rate was obtained with Navicula sp. U. lens and S. durum are both good settlement inducers, but are not sufficient to support rapid growth of young H. rubra post-larvae. Survival was low on U. lens and on the diatom C. closterium. We suggest that commercial nursery plates seeded with U. lens will result in high and consistent settlement, while an inoculum with Navicula sp. will ensure sufficient food for rapid growth of the post-larvae.