Some Evidence for Aquatic Macrophytes as Repellents for a Limnetic Species of Daphnia

Under controlled laboratory conditions Daphnia rosea SARS is strongly repelled by substances secreted by Elodea, Nitella, and Myriophyllum. This phenomenon can be easily demonstrated in a large glass U‐tube having a small sprig of hydrophyte at the surface of the water on one side of the U‐tube. It can also be demonstrated in a long narrow aquarium having an incomplete vertical plastic divider at the center, and with the hydrophyte on one side of the divider. Simulated plastic aquarium vegetation in control aquaria has only a slight repellent or „shading”︁ effect. The implications of this phenomenon in the hydrophyte zone of lakes and ponds are discussed.