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

Ciencias Marinas (2009), 35(1): 113–122

Nota de Investigación/Research Note
Effect of darkness on the early postlarval development of Haliotis corrugata abalone fed different diatom densities Efecto de la oscuridad sobre el desarrollo postlarval inicial del abulón Haliotis corrugata alimentado con diferentes densidades de diatomeas
E Gorrostieta-Hurtado, R Searcy-Bernal*, C Anguiano-Beltrán,Z García-Esquivel, E Valenzuela-Espinoza
Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Km 103 Carretera Tijuana-Ensenada, Apartado postal 453, Ensenada CP 22860, Baja California, México. * E-mail: rsearcy@uabc.mx

Abstract
Four-day-old postlarvae of the abalone Haliotis corrugata were exposed to different diatom densities (Navicula incerta, 0 to 8000cells 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 cellsmm–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 ratesin darkness reinforce the hypothesis that the nocturnal habits of abalone develop soon after metamorphosis and not at juvenile stages as usually considered. Key words: abalone, darkness, growth, Haliotis corrugata, postlarvae.

Resumen
Se realizó un experimento con postlarvas del abulón Haliotis corrugata de cuatro días de edad en dos condiciones de iluminación, luz continua (19 a 21 µmolquanta m–2 s–1) y oscuridad, y alimentados con diferentes densidades de diatomeas (Navicula incerta, 0 a 8000 cél mm–2), para evaluar el efecto de estos dos factores sobre la tasa de pastoreo, la supervivencia, y la tasa de crecimiento postlarvales. El experimento se llevó a cabo durante 14 días en cámaras estériles de 10 mL siguiendo un diseño de parcelas divididas con tres réplicas por tratamiento.El promedio máximo de la tasa de pastoreo se presentó con una densidad de 2000 cél mm–2, siendo mayor en la oscuridad (196 ± 67 cél pl–1 h–1) que en la luz (139 ± 36 cél pl–1 h–1). El promedio de supervivencia también fue mayor en la oscuridad (59%) que en la luz (44%), al igual que la tasa media de crecimiento (20 μm d–1 y 14 μm d–1, respectivamente). Al final del periodo experimental la tasa decrecimiento tendió a disminuir con el aumento de la densidad de diatomeas. Las mayores tasas de pastoreo y crecimiento en la oscuridad refuerzan la hipótesis de que los hábitos nocturnos en los abulones se desarrollan poco después de la metamorfosis y no hasta estadios juveniles como generalmente se considera. Palabras claves: abulón, crecimiento, Haliotis corrugata, oscuridad, postlarvas.Introduction
Juvenile and adult abalone have nocturnal habits and their most active feeding period begins at dusk and continues until they are satiated (Leighton 2000). Research conducted on juveniles and adults of different species of abalone has shown that in a dark environment the feeding rate can be from 0.9% to 24.1% higher and the growth rate from 16% to 259% higher than under light conditions(Kim et al. 1997, Huchette 2003, García-Esquivel et al. 2007). Whether postlarval abalone have similar nocturnal habits as those of juvenile and adult abalone is not known; however, experiments have shown that the grazing rate of 6-day-old Haliotis rufescens postlarvae is 37%

Introducción
Los abulones juveniles y adultos tienen hábitos nocturnos y su periodo de alimentación más activo...