Methods and devices for cultivating coenocytic algae

The present invention concerns methods and devices for cultivating coenocytic algae and for producing cellulose, in particular microfibrillated cellulose (MFC). In one embodiment, the algae are grown on a solid substrate immersed in liquid culture medium. The solid substrate preferably comprises a carbonite mineral. The invention also concerns a method for producing spores of said coenocytic algae and a device comprising two separate containers, a first container for growing said algae and a second container for growing larger algae and inducing the generation of spores.