Drought-Induced, Punctuated Loss of Freshwater Mussels Alters Ecosystem Function Across Temporal Scales

Abstract

Punctuated, mass mortality events are increasing for many animal taxa and are often related to climatic extremes such as drought. Freshwater mussels are experiencing increased mass mortality events linked to hydrologic drought. Because mussels play important functional roles in rivers it is important to understand the ecosystem effects of these die-offs. Here, we address how mass mortality events of mussels caused by drought may impact stream ecosystem function. We first present a conceptual model, based on the literature, of how mussel mass mortality should affect different ecosystem functions across various ecological time scales, from hours to decades. Next, we highlight two case studies of drought-linked, mussel-mass mortality events from rivers in the southern U.S. We then present the results of an experiment we performed quantifying the ecosystem effects of a punctuated mussel die-off. Finally, we combine our experimental results with field data from a recent mussel die-off to predict how mussel losses will influence ecosystem function. Based on the presented case studies, our mesocosm experiment, and our extrapolated nutrient pulse due to a mussel die-off, we conclude that stream ecosystems are extensively altered following mussel mass mortality events. Mussel loss is governed by drought severity, location within the river network, and species-specific drought tolerances. In the short term, decomposing carrion from mussel die-offs releases a large pulse of nutrients into the water which stimulates food web productivity. In the long term, the overall loss of mussel biomass, and the loss of functional traits as more sensitive species decline, leads to decreases in ecosystem function which may take decades to recover. Drought and human demand for water will make mussel die-offs more likely in the future and it is unlikely that drought sensitive species will recover without changes in water management and restoration of populations through mussel propagation. Our research provides an example of how the loss of an abundant, long-lived organism has cascading, and long-term impacts on ecosystems.

Evolutionary history drives aspects of stoichiometric niche variation and functional effects within a guild

“…Most climate change projections for the southeastern United States predict increasing drought and that the frequency of both above‐ and below‐median flows will increase (Golladay et al 2016), suggesting an increase in disturbance frequency. Given these projections, we may anticipate shifts in communities dominated by long‐lived, equilibrium species to communities dominated by short‐lived periodic species based on life‐history strategies (DuBose et al 2019). However, predictions based on response traits may be in conflict to those made based on life‐history strategies.…”

Conservation planning in an uncertain climate: Identifying projects that remain valuable and feasible across future scenarios

“…The Red River is a semi‐arid, drought‐prone river where water availability is geographically skewed: western reaches are arid and can receive as little as 400 mm of rain per year, while eastern reaches can receive up to 1,600 mm (PRISM Climate Group, 2019). Additionally, the combination of consumptive societal water use and extreme thermal and flow regimes in this region can create harsh conditions for aquatic biota (DuBose et al., 2019; Matthews & Marsh‐Matthews, 2017; Matthews et al., 2005). The Red River has a high density of reservoirs which were constructed for flood control and to provide water storage to meet societal water demands.…”

“…Additionally, the combination of consumptive societal water use and extreme thermal and flow regimes in this region can create harsh conditions for aquatic biota (DuBose et al, 2019;Matthews & Marsh-Matthews, 2017;Matthews et al, 2005). The Red River has a high density of reservoirs which were constructed for flood control and to provide water storage to meet societal water demands.…”

Mass Mortality Events of Invasive Freshwater Bivalves: Current Understanding and Potential Directions for Future Research

“…It is important to note that mass mortality events are not unique to invasive bivalves, and can also occur with native bivalve species (e.g., Vaughn et al, 2015in Oklahoma, Sousa et al, 2018 in the Iberian Peninsula). While this review focuses on mass mortality events of invasive bivalves, a critical and open research question is to what extent the responses of native and invasive bivalves may differ and or interact (DuBose et al, 2019). Generally speaking, mass mortality events of invasive bivalve species were triggered by extreme abiotic conditions, including drought, flood, extreme high temperatures, and extreme low temperatures (Figure 1).…”