Thermal preference increases during larval development of pure and hybrid abalone

Temperature is one of the main factors influencing biological processes of ectothermic species. An optimum temperature of 16-18°C has been suggested for the development of early life stages of temperate Australian abalone, yet there are little physiological or behavioral data to support this suggestion. This study examines the acute thermal preferences (Tpref), swimming speeds (U), and oxygen consumption rates (MO 2 ) of veliger larvae of blacklip abalone [Haliotis rubra (Leach, 1814)], greenlip abalone [Haliotis laevigata (Donovan, 1808)] , and their interspecies hybrid. Thermal preference and U were measured in a thermal gradient with temperatures ranging from 12°C to 25°C, and MO 2 was measured at 4-7 temperatures between 12°C and 32°C. Thermal preference increased in all three groups of abalone during development from a Tpref of 16°C in 1-day-old early veligers to a Tpref of 20°C in 3-day-old late veligers. Swimming speed increased with temperature in all three groups of abalone and increased with age in H. rubra and hybrids but not in H. laevigata. Veliger MO 2 increased throughout the ecologically relevant temperature range in all three abalone groups. Higher temperatures were examined in hybrids, and it was found that MO 2 reached a peak at 25°C and declined thereafter. These results align with the temperatures that veligers may experience in their natural habitat and provide support that current temperatures maintained at Australian aquaculture hatcheries are within optimal ranges for larval performance.