Diet of Melanoides tuberculata (Müller, 1774) from subtropical coastal lakes: Evidence from stable isotope (δ13C and δ15N) analyses

Freshwater gastropods, through their indiscriminate deposit feeding, provide an essential link between available benthic resources and higher trophic levels in a variety of aquatic habitats. Here we focus on the contribution of available sources to the diet of Melanoides tuberculata in different habitats within coastal subtropical lakes. Globally, this species is one of two dominant alien invasive thiarid gastropods that have established populations in diverse habitats across the New World. We assessed the dietary composition of M. tuberculata to provide insight on the ability of this species to utilize a range of resources under different environmental conditions as a factor that contributes towards its invasion success. Our results show that M. tuberculata exhibits a degree of trophic plasticity and that its diet is largely determined by the availability of resources. However, all sources were not consumed in equal proportions. Benthic microalgae and filamentous Cladophora sp. dominated the diet of snails inhabiting the shallow stream-fed habitats, with sedimentary organic matter making a significantly lower contribution. In contrast, detritus was the most important food source for individuals from the littoral zone of an oligotrophic lake. Although M. tuberculata exhibits trophic plasticity, there is evidence for specialization in diet between individuals within small spatial scales. These variations may contribute to the overall invasion success of this species, by reducing intraspecific competition for resources following introduction to new habitats.