CONTRIBUTION TO THE KNOWLEDGE OF PHYTOPLANKTON DIGESTION IN EARLY LARVAE OF MYTILUS EDULIS

Abstract

The digestion of several species of monocellular algae has been closely followed in young veligers of Mytilus edulis. The larvae were observed by microfluorescence microscopy, since the fluorescence of ingested algae, visible through both the transparent shell and flesh, varies throughout digestion. The larvae once fed were placed in 0.2 mμ filtrcd sea water and sampled at different times. It was observed that the intensity of the algal fluorescence changed from a deep red to a pale rose, and later disappeared. These fluorescence variations were arbitrarily classed into 4 qualitative stages of digestion. Thin and ultra thin sections were made from many larvae representative of the previously mentioned digestion stages. These sections, observed by both light and transmission electronic microscopy, shows the various degrees of degradation of the algae in the interior of the larval stomachs. The histological observations are discussed and compared to the results obtained using epifluorescence microscopy. It was concluded that the differences in fluorescence intensity are indicative of the degree of algal digestion.