A new experimental approach to investigate grazing on epiphytic lichens by gastropods in a controlled laboratory environment

Abstract The grazing impact on epiphytic lichens by a non-native gastropod species is documented and quantified for the first time in the province of Newfoundland and Labrador using a unique combination of a multiple-choice feeding design with lichen transplant techniques under controlled laboratory conditions. The feeding experiment included three arboreal lichen species sewn onto a mesh and attached to red maple sticks inside a terrarium where four Cepaea nemoralis snails were introduced and allowed to graze over a five-day period. The three lichen species used in the feeding trials included the green-algal Platismatia glauca , the cephalolichen Lobaria pulmonaria , and the cyanolichen Lobarina scrobiculata. The trials also included two sets of L. pulmonaria from different regions of the island of Newfoundland. The levels of grazing and preference by the snails was very high. Herbivory was high for all lichen species but was highest for Platismatia glauca , for which 70% of thalli were consumed after only 24 hours. Our results show that C. nemoralis is probably affecting the distribution and abundance of epiphytic lichens in the forests of Newfoundland and Labrador. Furthermore, our observations of intense herbivory on reproductive structures challenges the universal application of the optimal defence theory in lichens.