Long‐term forecast of thermal mortality with climate warming in riverine amphipods

Abstract

Forecasting long-term consequences of global warming requires knowledge on thermal mortality and how heat stress interacts with other environmental stressors on different timescales. Here, we describe a flexible analytical framework to forecast mortality risks by combining laboratory measurements on tolerance and field temperature records. Our framework incorporates physiological acclimation effects, temporal scale differences and the ecological reality of fluctuations in temperature, and other factors such as oxygen. As a proof of concept, we investigated the heat tolerance of amphipods Dikerogammarus villosus and Echinogammarus trichiatus in the river Waal, the Netherlands. These organisms were acclimated to different temperatures and oxygen levels. By integrating experimental data with high-resolution field data, we derived the daily heat mortality probabilities for each species under different oxygen levels, considering current temperatures as well as 1 and 2°C warming scenarios. By expressing heat stress as a mortality probability rather than a upper critical temperature, these can be used to calculate cumulative annual mortality, allowing the scaling up from individuals to populations. Our findings indicate a substantial increase in annual mortality over the coming decades, driven by projected increases in summer temperatures. Thermal acclimation and adequate oxygenation improved heat tolerance and their effects were magnified on longer timescales.Consequently, acclimation effects appear to be more effective than previously recognized and crucial for persistence under current temperatures. However, even in the best-case scenario, mortality of D. villosus is expected to approach 100% by 2100, while E. trichiatus appears to be less vulnerable with mortality increasing to 60%. Similarly, mortality risks vary spatially: In southern, warmer rivers, riverine animals will need to shift from the main channel toward the cooler head waters to avoid thermal mortality. Overall, this framework generates high-resolution forecasts on how rising temperatures, in combination with other environmental stressors such as hypoxia, impact ecological communities.

Intraspecific variation of heat tolerance in a model ectotherm: The role of oxygen, cell size and body size

“…by promoting tracheal oxygen conductance (Harrison et al, 2018). Such compensatory changes may have delayed the onset of tissue hypoxemia and thus improved heat tolerance as has been recently shown to improve heat tolerance in amphipods (Verberk et al, 2023). Despite such compensation, hypoxia still reduced survival of mild heat stress, providing support for our third hypothesis.…”

“…Evidence supporting oxygen limited thermal tolerance is stronger for aquatic breathing arthropods than for those that breath air (Frederich & Pörtner, 2000;Giomi et al, 2014), but few of those studies have tested this hypothesis experimentally using TDTs curves (e.g. Semsar-Kazerouni et al, 2020;Verberk et al, 2023).…”

“…However, explicitly incorporating time may be useful beyond comparative studies and prove helpful in elucidating the mechanisms of thermal death in ectotherms either by increasing the signal-to-noise ratio or because the mechanistic basis underlying physiological death during a thermal stress may be context-dependent, varying as a function of the intensity and specific duration of the thermally stressful event. For instance, benefical effects of thermal acclimation where found to be more pronounced in longer trials with mild heat stress than in trials focussing on acute, intense heat (Verberk et al, 2023).…”

Fitness surfaces and local thermal adaptation in Drosophila along a latitudinal gradient

“…Blanquart et al., 2013; Crozier, 2004; Kawecki & Ebert, 2004; O'Brien et al., 2017; Purcell & Avilés, 2008), the proposed approach should enhance our ability to predict how different organisms may cope with environmental conditions outside their distribution range or predict how they might respond to future climate change scenarios. Importantly, the analytical framework can be expanded to include other environmental factors, which may interact with heat stress and increase vulnerability to warming such as hypoxia (Verberk et al., 2023) or nutrient deficit (Koussoroplis et al., 2023). Furthermore, these analyses may take advantage of available published data to obtain comparable fitness metrics across lineages or environments, which may open the venue to quantify fitness surfaces in space or time, vulnerability to environmental change, invasive potential, coexistence or competitive displacement (see also Bellis et al., 2023).…”

Predicting organismal response to marine heatwaves using mechanistic thermal landscape models

“…The dynamic tolerance model approach is likely to produce more accurate predictions of organism mortality within an environmental context and has shown promise in scaling the physiological effects of climate change across ecological scales. Dynamic tolerance models predicted mortality events with current and future water temperature scenarios in Venice Lagoon bivalves (Bertolini et al, 2023), Antarctic marine invertebrates (Carter et al, 2023;Molina et al, 2022), and lotic amphipods (Verberk et al, 2023). There has been a single application of dynamic tolerance models to MHWs that explicitly investigated the potential for mismatches between categorization based on the 90 th percentile of climatology and modelled mortality (Bertolini & Pastres, 2021).…”