Papyrus wetlands a lunar-modulated refuge for aquatic fauna

Abstract

A field study was undertaken of the use of papyrus (Cyperus papyrus) wetlands fringing Rubondo Island, Lake Victoria, Tanzania, as a refuge from predators by freshwater shrimps (Caridina nilotica) and tilapia (Oreochromis niloticus) larvae. During the full moon nights, fish larvae took refuge more than 5 m in the papyrus and did not venture out into the lake, while they ventured into fringing lake waters during moonless nights. The freshwater shrimps and lake flies (Chaoborus sp.) did not migrate with the moon. This fauna took refuge in the papyrus wetlands even though the dissolved oxygen concentration was as low as 0.4 ppm (<5% of saturation).