Enigmatic freshwater mussel declines could be explained by the biodiversity‐disease relationship

Abstract

The biodiversity‐disease relationship states that increased species richness leads to lower pathogen pressure (i.e. the dilution effect), an effect that erodes with biodiversity loss. However, whether losses of the dilution effect can trigger extinction cascades remains largely unexplored. To explore this idea, we consider declines in freshwater mussels, on average the most threatened non‐marine group of organisms in the world. We argue that anthropogenically stimulated declines in mussel richness amplify pathogens in remaining species. Pathogen amplification triggers further local losses in both mussel abundance and richness, explaining the observed so‐called “enigmatic” declines in freshwater mussels. Vulnerable communities could become trapped in cycles of pathogen amplification and host decline. We highlight knowledge gaps and provide key steps to assess the likelihood of this occurring; these key steps are applicable to any host group. Policy implications. Our argument constitutes a testable hypothesis that may explain richness or abundance declines in previously intact communities. We provide further impetus for the consideration and preservation of diversity at a local scale and show that effective conservation requires integration of both host and parasite ecology.

Results of a Mussel Survey from the Upper Rock River, Wisconsin and Illinois, and the Discovery of Live Cyclonaias tuberculata (Purple Wartyback)

“…Mussels typically occur in dense multispecies beds which perform numerous ecological functions such as biodeposition, nutrient cycling, and acting as food and habitat for other organisms (Atkinson et al 2023, Vaughn 2018, Vaughn and Hakenkamp 2001). Unfortunately, mussels are one of the most heavily impacted organisms globally, with ∼70% of North America's ∼300 species currently considered imperiled to some degree (Brian and Aldridge 2023, Haag 2012, Lopes-Lima et al 2018). Declines have been linked to numerous factors, including habitat destruction and alteration, pollution, climate change, over-harvest, and competition with invasive species (Haag 2012, 2019; Strayer et al 2004).…”