Interactions between Unionida and non-native species: A global meta-analysis

Understanding the multiple agents of decline is important for the conservation of globally threatened Unionida (Class Bivalvia), but threats from non‐native species have received limited attention. To address this gap, a global meta‐analysis was conducted aimed at identifying known interactions and mechanisms of impact and informing potential effect pathways for the New Zealand unionid fauna. The main non‐native groups identified as interacting with unionids were fish (38% of published studies), macrophytes (33%), and vertebrate predators (30%), with ~70% of interactions leading to adverse impacts on mussels. Most studies used field surveys (~50%) and were conducted in rivers (~50%). Impacts occurred across the unionid life cycle (adult, glochidia, host, and juvenile), and primarily affected processes that determine the transitions between life‐cycle stages (fertilization, infestation, settlement, and maturation). The impacts of non‐native macrophytes and fish were predicted to be greater for transitional stages than the impact of vertebrate predators, which mostly affected adult mussels. New Zealand Unionida are most likely to be affected by interactions with non‐native species in lowland lakes and waterways, where connectivity for diadromous native fish hosts and high bioinvasion potential intersect.