Dietary value of benthic diatoms for the growth of post-larval abalone Haliotis discus hannai

Abstract

The feeding behaviour and the growth of post-larval abalone (1–2 mm in shell length) Haliotis discus hannai fed on nine species of benthic diatom were examined in the laboratory. Digestion efficiencies of abalone fed on the nine diatom species were also measured. All abalone showed active feeding behaviour and diatom cells were observed in their stomachs. However, the growth rates of abalone fed on four diatom species, which were readily digested, were higher than those of abalone fed on the other five species of diatom. The cell walls of the former four diatom species were easily broken open when they were grazed by abalone because of their high adhesive strength (three species), or due to the weakly silicified cell walls (one species with a low adhesive strength). The other five species, whose adhesive strengths are low, were easily ingested by abalone without any deformation of the cell walls and the majority of them were excreted whole and still alive. It is considered that post-larval abalone cannot digest diatom cell contents in their alimentary canal without first rupturing the cell wall with the radula. It is thought that the post-larvae which ingested the latter five diatom species could not readily absorb the diatom cell contents as the cell wall was intact and thus their growth rates were low.