A photobioreactor is described for cultivating phototrophic organisms and in particular a mat, as can be used in one such photobioreactor. The mat has a plurality of first fibres which are light conductive along their longitudinal direction and are constructed to decouple light conducted in the longitudinal direction laterally, at least somewhat transversely to the longitudinal direction. The mat furthermore has a plurality of second fibres which are electrically conductive along their longitudinal direction. With the aid of one such mat, light can on the one hand be coupled in the interior of a photobioreactor. On the other hand, a travelling electric alternating field can be generated by applying a suitable polyphase voltage by means of a voltage source with the aid of electrically conductive second fibres. This alternating field can act on electrically charged particles.
