A vampire with a solar cell

Without any shell or a house, the sea slug known as Elysia viridis wriggles its way through the kelp forest in the Trondheims Fjord, the third longest fjord in Norway. The slug’s translucent white body seems vulnerable and soft. In reality, that is its greatest advantage. In fact, the sea slug can live for nine months without food, precisely because it is 'naked'. This discovery was made by scientists at the Trondhjem Biological Station at the Norwegian University of Science and Technology (NTNU).

A sweet tooth

The sea slug’s favourite food is an alga called 'dead man's fingers'. Algae get energy from the sun, just like plants that live on dry land. Some teeny tiny green grains inside the algae cells see to it that the algae get food when the sun shines. The grains are called chloroplasts and they make sugar from water, air and sunlight.

When the sea slug eats the algae called dead man's fingers, something strange happens. Kind of like a vampire, the slug bites a hole in the algae cells with its mouth and then slurps up the contents. Most of the algae are digested in the usual manner, but not the green chloroplasts. They remain active in the slug’s intestinal cells for a long time.

Food for the lazy

Elysia viridis's intestines occupy large parts of the translucent slug's body, so the chloroplasts get plenty of sunlight. Thus the green grains continue making sugar inside the intestinal cells as though nothing had happened. All the slug has to do is to relax in the sunshine. It gets all the food it needs directly from its own personal solar cell!

Published in 'Nysgjerrigper' no. 3/08

Translated by Linda Sivesind