Effect of damage by the snail Lymnaea ( Lymnaea) stagnalis (L.) on the growth of Elodea canadensis Michx.

Abstract

The response of Elodea canadensis to grazing damage from the snail Lymnaea ( Lymnaea) stagnalis was analysed in laboratory experiments. The type and degree of damage to Elodea as well as the post-damage growth of the plants were examined. Lymnaea (2–3 g fresh weight) consumed 35–260 mg fresh weight of Elodea daily . More than 90% of the plant material remaining after snail grazing bore clear signs of damage, with over 70% showing more than one kind of injury. Fragmentation of plants was noted most frequently, followed by damage to leaves and growing tips. Grazing scars on the surface of stems occurred more rarely. Both naturally grazed plants and those damaged experimentally (with removed parts of leaves and/or growing tips) exhibited high survival and growth rates. Subsequent to damage, growth occurred mainly through the formation of new lateral shoots. Most (71%) plant fragments remaining after snail grazing were still alive after 35 days of exposure. Those that died without generating lateral shoots were mainly small pieces of the lower (hence oldest) parts of stems.