Effect of darkness on the early postlarval development of Haliotis corrugata abalone fed different diatom densities

Abstract

Four-day-old postlarvae of the abalone Haliotis corrugata were exposed to different diatom densities (Navicula incerta, 0 to 8000 cells mm^–2) under two illumination conditions: constant light (19–21 µmol quanta m^–2 s^–1) and darkness. The effect of these two factors on postlarval grazing rate, survival, and growth was evaluated. The experiment was conducted for 14 days in 10-mL sterile wells following a split-plot experimental design with three replicates per treatment. The highest grazing rate was observed in the 2000 cells mm^–2 density treatment and it was higher in darkness (196 ± 67 cells pl^–1 h^–1) than in constant light (139 ± 36 cells pl^–1 h^–1). Mean survival was also higher in darkness (59%) than under constant light (44%), as was mean growth rate (20 and 14 µm d^–1, respectively). Growth rate at the end of the experimental period tended to decrease with the increase in diatom density. Higher grazing and growth rates in darkness reinforce the hypothesis that the nocturnal habits of abalone develop soon after metamorphosis and not at juvenile stages as usually considered.