Volvox bloom

Volvox is a popular alga among microscopists because of the beautiful images it produces under the microscope. The volvox in the video was unexpectedly found in a pool in Eindhoven, the Netherlands in early November 2019. There were so many of these species present that one could speak of a bloom.

The green alga Volvox is a colony of cells that have started to work together. Some cells catch the light, others provide movement or reproduction. They have become so dependent on each other that you can speak of a multicellular organism.

Some "colonies" are no more than a collection of cells that do exactly the same, but the spherical Volvox is different. Cells work together there and specialize. All cells are on the outside of the sphere. There are cells with whip hairs or cilia for movement and cells that provide for reproduction.

In good times, germ cells immediately grow into daughter colonies that float inside the mother globe. They continue independently as the parent colony opens and then dies. As the winter approaches, sex comes around the corner. The germ cell changes into a packet of sperm cells, or enlarges to an egg cell. Sperm cells are released and swim to the eggs to fertilize them. The fertilized egg forms a hard, thick wall. Volvox can survive winter well in this capsule.

With thanks to Harry Nouwen, Royal Dutch Natural History Association