Abstract
The larval preference for substrata which were coated by the cultured attaching diatoms, Navicula ulvacea, N. sp. and Achnanthes brevipes was studied through a choice test to clarify the relationship between the preference for the settlement and the attaching diatom. These attaching diatoms were cultured in a unialgal condition. The settlement index was defined as the difference between the numbers of larvae which settled on the film-coated and not film-coated glass slides.The index was obtained for the effect of the attaching diatom film and attaching bacteria which propagated on the glass slides together with the attaching diatom.
There was a semi-logarithmic linear relationship between the settlement index and the density of each attaching diatom over a certain level of density. We thought that the larvae preferred the cultured attaching diatom for the settlement, because there was no clear effect of only attaching bacteria on the settlement.
