Insect herbivory on native and exotic aquatic plants: phosphorus and nitrogen drive insect growth and nutrient release

The invasive clam Corbicula fluminea causes severe environmental and economic impacts in invaded sites and fouled water-dependent industries. The biological control of invasive species has potential as an effective, safe and low-cost tool. The potential of using direct (clam consumption) and indirect approaches (predator-avoidance behaviour) to control the pest was evaluated, aiming at establishing a proof-of-principle regarding the suitability of such strategies in confined settings (e.g. pipelines, channels, raw water tanks and other water-dependent facilities). Invertebrate (Procambarus clarkii) and vertebrate (Lepomis gibbosus, Luciobarbus bocagei) predators were examined for their control potential. In feeding experiments, barbels foraged upon C. fluminea but ingested very few clams, and clam consumption by crayfish was only observed in the smallest size class (<1 cm). Additional experiments linked these results to the protective role of the clam’s shell. In practical terms, the potential of the fish species as C. fluminea predators is limited, but crayfish can be important predators of small clams. In a second set of experiments, putative predator avoidance by clams was assessed in dual-choice aquaria. Refuge availability, predator diet and light conditions were taken into account. Clam avoidance was observed under particular conditions, but the amplitude of dislocation was limited.