DIATOM DIET OF ABALONE POST-LARVAE (HALIOTIS-MIDAE) AND THE EFFECT OFPRE-GRAZING THE DIATOM OVERSTORY

Gut content analyses of abalone post-larvae (H. midae) that settled on diatom-covered surfaces were conducted to determine selectivity in fe eding. Diatoms were counted by the Utermohl method and scanning electr on microscopy was used for their identification. Results indicated tha t abalone post-larvae preferred prostrate diatoms such as Cocconeis su blittoralis Hendey, Amphora proteoides Hustedt and Achnanthes brevipes Agardh but would consume the more loosely packed, overstorey species such as Delphineis karstenii (Boden) Fryxell, Diploneis placida (Schmi dt) Hustedt and Nitzschia palea (Kutzing) Wm. Smith if their preferred food was not available. Pre-grazing of settlement surfaces by juvenil e abalone before the introduction of larvae removed most of the overst orey diatoms but left the preferred species virtually intact.