Comparing freshwater mussel responses to stress using life-history and Dynamic Energy Budget theory

Freshwater mussels are experiencing severe population declines, affecting their critical role in freshwater ecosystems. A thorough assessment of threats posed by various stressors is needed; however, the large number of species to be considered and significant data gaps, especially for listed species, hinder the process. We combined a traits-based approach to represent multiple species grouped into three life-history categories - Equilibrium, Opportunistic, and Periodic - with the Dynamic Energy Budget modeling principles to capture the physiological mechanisms driving individual-level responses. We used the DEB model to simulate individual life cycles and explore relationships between underlying energetics and emerging individual traits of 47 freshwater mussel species and the common toxicity test surrogate, the Eastern oyster (Crassostrea virginica), under control and stressed conditions. Stress was introduced via physiological modes of action related to four key metabolic pathways: energy assimilation, maintenance, growth, and reproduction. We recorded maximum length, age at maturity, and fecundity and compared these endpoints and their stress-induced changes among life-history categories. The life-history differences among freshwater mussels directly emerged from underlying energetics, with high assimilation and maintenance supporting opportunistic traits. Stress imposed on energy assimilation had the strongest effect on all life-history traits, and a 25 % reduction in assimilation rate resulted in an average 25 % and 60 % decrease in maximum length and fecundity, respectively, and a 24 % increase in age at maturity. Equilibrium species suffered the greatest negative effects overall, indicating that this life-history strategy might be the most susceptible to stressors. The Eastern oyster displayed extreme opportunism in its life-history traits, but its responses to stress were generally within the range observed for freshwater mussels. The study provides a much-needed general understanding of stress responses across freshwater mussel life-history categories and contributes to the foundation for developing life-history-driven population models.