Grape seed extract and dried macroalgae, Ulva lactuca Linnaeus, improve survival of greenlip abalone, Haliotis laevigata Donovan, at high water temperature

•Grape seed extract reduces mortality of greenlip abalone at high water temperatures.•Dried Ulva lactuca also improved survival at high temperatures.•Grape seed extract was more efficient than dried Ulva lactuca.•Information to be used to reduce mortality at high summer water temperatures on-farm

Summer mortality (SM) in greenlip abalone (Haliotis laevigata Donovan) heavily affects productivity of land-based abalone farms in Southern Australia. It has been associated with conditions of high water temperature (> 23 °C), low dissolved oxygen levels, and a range of other stressful factors in the culture water during summer months. This study aimed to alleviate mortality experienced by abalone at high water temperatures (26 °C), by dietary intervention using grape seed extract (GSE) and dried Ulva lactuca Linnaeus, two products which contain antioxidative and bioactive compounds. These products were formulated into a commercial abalone diet at levels of 5 and 30%. The diets were fed to 3-year-old greenlip abalone (26.8 g; 57.9 mm) at a water temperature of 22 or 26 °C for 38 days. No mortalities were observed at 22 °C. Compared to the unaltered commercial diet, both GSE and dried U. lactuca additive diets significantly increased the survival of abalone at the 26 °C water temperature (P < 0.05). GSE addition also significantly increased serum superoxide dismutase activity, feed intake, and meal acceptance of the abalone (P < 0.05). These results demonstrate the potential for GSE or dried U. lactuca to act as dietary additives to reduce mortality and improve productivity on abalone farms subjected to high summer water temperatures.