The role of photosynthesis in the nutrition of the mollusc Elysia viridis

Experiments were carried out on the changes in weight, chlorophyll content and photo-synthetic capacity of Elysia viridis over periods of up to 8 weeks when incubated in light or dark, with and without its source of chloroplasts, the seaweed Codium fragile. It was concluded that photosynthesis is of considerable importance in the nutrition of the animal. Animals starved in the dark lost weight much more rapidly than those starved in the light. Rates of photosynthesis are of the right order to account for these differences in weight. The animal seems to have an annual life-cycle, an important consideration in analysing the results of long term experiments carried out on animals collected at different times of the year.