Observations on ingestion and digestion of unicellular algae by Strombus gigas larvae (Mollusca, Gastropoda) using epifluorescence microscopy

Abstract Epifluorescence microscopy was used to observe the ingestion and digestion of unicellular algae in gastropod larvae. Larvae started feeding 8 h after hatching. Three kinds of diet were tested during the period of this study: Isochrysis aff. galbana, Tetraselmis chuii and Isochrysis-Tetraselmis mixture. All the experiments were conducted at 29°C. It was shown that ingestion was faster with Tetraselmis than with Isochrysis . Within 10 min 43% of the larvae had ingested Tetraselmis and no larvae had ingested any Isochrysis . Within 30 min, 60% of the larvae had ingested Tetraselmis while only 25% had ingested Isochrysis . Using a scale based on the quality of fluorescence, it was possible to determine the time interval to digest a diet, which is shorter with Tetraselmis than with Isochrysis . After 8 h the digestion index reached 45% for larvae fed with Tetraselmis while it was only 28% for larvae fed with Isochrysis . Using a quantitative scale based on measurements of the fluorescent surface in each larva, it was demonstrated that the amount of diet ingested is higher with Tetraselmis than with Isochrysis . These results indicate that Tetraselmis chuii forms an adequate diet for young veligers of Strombus gigas .