The settlement of abalone (Haliotis discus hannai Ino) larvae on culture layers of different diatoms

An innovative method was developed to quantitatively measure the attractiveness of cultured diatoms for early stages of abalone larvae settlement. Larvae of the abalone Haliotis discus hannai were offered, in a petri dish, a choice of several food patches, each made of a diatom monoculture layer. The distribution of the larval settlement on the patches of 17 diatom species was determined. Nitzschia laevis induced the most abalone larvae settlement, followed by Navicula cf lenzii and Amphora luciae. The attractiveness of these diatoms for abalone larvae settlement was not directly related to algal biochemical composition or algal color. It is suggested that compounds excreted by algal cells determine their inductive properties for larval settlement. The larval chemosensory response depends on the concentration of these inductive substances. Sonicated diatom cell suspensions strongly induced larvae attachment, whereas dilute suspensions did not. Boiling settlement-inductive sonicated diatom cell suspensions did not affect their induction ability, implying that native proteins are not essential for the response. Aspartic acid was the only free amino acid excreted by two tested diatoms. It was also the only pure amino acid found inductive for larval settlement. It is therefore suggested that aspartic acid is a component of the settlement induction complex.