Boundary layers and abalone postlarval culture: Preliminary studies

Abstract

In general, the surfaces of any solid immersed in water are covered by boundary layers that are minimally affected by water motion in the system, and in which dissolved molecules are transported mainly by diffusion. Microgradients of environmental conditions within diffusive boundary layers on the surfaces on which abalone ( Haliotis spp.) postlarvae are cultured might severely affect their fitness, despite the provision of aeration or water flow. Preliminary studies are presented where microelectrodes are used to determine the oxygen conditions above surfaces colonized by benthic diatoms on which abalone postlarvae are cultured. Oxygen saturation within 1 mm of the diatom surface reached 180%, while elsewhere 100% saturation prevailed. A sudden reduction of illumination from 59 to 4 μE s −1 m −2 produced a drop in oxygen saturation at the diatom surface from 140 to 50% in only 3 min. The possible implications of these and other results on the management of postlarval culture systems for abalone are discussed.