An aquatic biofiltration system where invertebrate aquatic filtering organisms in the form of tunicates filter free-floating particulates in a water volume is disclosed. The system provides a habitat for tunicates with at least one residence device (5, 6) adapted to be arranged in a water volume, and a collection system (7) adapted to collect expelled solids from the tunicates. A biofiltration method for filtering particulates from a volume of water is also disclosed.