• Energy Research

AbstractClimate change is intensifying extreme weather events, including marine heatwaves, which are prolonged periods of anomalously high sea surface temperature that pose a novel threat to aquatic animals. Tropical animals may be especially vulnerable to marine heatwaves because they are adapted to a narrow temperature range. If these animals cannot acclimate to marine heatwaves, the extreme heat could impair their behavior and fitness. Here, we investigated how marine heatwave conditions affected the performance and thermal tolerance of a tropical predatory fish, arceye hawkfish (Paracirrhites arcatus), across two seasons in Moorea, French Polynesia. We found that the fish’s daily activities, including recovery from burst swimming and digestion, were more energetically costly in fish exposed to marine heatwave conditions across both seasons, while their aerobic capacity remained the same. Given their constrained energy budget, these rising costs associated with warming may impact how hawkfish prioritize activities. Additionally, hawkfish that were exposed to hotter temperatures exhibited cardiac plasticity by increasing their maximum heart rate but were still operating within a few degrees of their thermal limits. With more frequent and intense heatwaves, hawkfish, and other tropical fishes must rapidly acclimate, or they may suffer physiological consequences that alter their role in the ecosystem.

# **Despite plasticity, heatwaves are costly for a coral reef fish** ## Description of the Data and file structure Author Information A. Principal Investigator Contact Information Name: Dr. Erika Eliason or Dr. Deron Burkepile Institution: University of California, Santa Barbara Email: [eliason@ucsb.edu](mailto:eliason@ucsb.edu), [dburkepile@ucsb.edu](mailto:dburkepile@ucsb.edu) B. Corresponding Author Contact Information Name: Jacey Van Wert Institution: University of California, Santa Barbara Email: [jcvanwert@gmail.com](mailto:jcvanwert@gmail.com) Date range of data collection (single date, range, approximate date): 2019-2022 Geographic location of data collection: Mo'orea, French Polynesia File List: VanWert_etal_2023_hawkfish.csv - contains hawkfish collection and morphology data, SMR, MMR, AAS, SDA metrics, and cardiac thermal tolerance test metrics ## METHODOLOGICAL INFORMATION 1. Description of methods used for collection/generation/processing of data: Hawkfish (*Paracirrhites arcatus*) were collected in Mo'orea, French Polynesia during Austral winter (2019) and Austral summer (2022). They were acclimated to one of five treatments (27, 28, 29, 31, or 33°C) for one week and tested for metabolic performance metrics, including maximum metabolic rate (MMR), standard metabolic rate (SMR), and costs of digestion (specific dynamic action, SDA) using custom-made respirometry chambers. A subset of fish was also tested for thermal tolerance using an acute cardiac thermal tolerance test. In addition, wild fish were also caught and tested for acute cardiac thermal tolerance. Metabolic data were processed in R and heart rate data were processed in LabChart. Please refer to the main manuscript for details regarding the methods used to collect and analyze this data. 2. People involved with sample collection, processing, analysis, and/or submission: Jacey C. Van Wert, Kim Birnie-Gauvin, Jordan Gallagher, Emily A. Hardison, Kaitlyn Landfield, Deron E. Burkepile, and Erika J. Eliason ## DATA-SPECIFIC INFORMATION FOR: VanWert\_etal\_2023\_hawkfish.csv 1. Number of variables: 22 2. Number of cases/rows: 76 3. Variable List: hawkfish_no = unique fish ID year = year of fish collection and measurements season = Austral summer (summer) or Austral winter (winter) treatment_new = acclimation temperature; 'wild' indicates fish were not acclimated and were collected from the wild and immediately tested bw_g = wet mass of fish (units g) tank = fish tank ID during acclimation tl_cm = total length of fish (units cm) sl_cm = standard length of fish (units cm) chase_pre_v_post = whether exhaustive exercise chase occurred before (pre) or after (post) SMR measurements mmr_corrected = body mass corrected maximum metabolic rate by universal metabolic scaling coefficient of 0.89 (units mg O2 kg-1 min-1) smr_low10_all = standard metabolic rate (units mg O2 kg-1 min-1) aas_corrected = absolute aerobic scope (units mg O2 kg-1 min-1) fas = factorial aerobic scope calculated as mmr/smr (unitless) percent_bw_scallop_fed = percent of body weight scallop fed for SDA trial SDA_integrated = integral of specific dynamic action (SDA) (units mg O2 kg-1) SDA_duration = duration of specific dynamic action (SDA) (units hours) peak_SDA_max = maximum metabolic oxygen consumption (MO2) reached during specific dynamic action (SDA) (units mg O2 kg-1 min-1) time_peak_SDA_max = time at which peak_SDA_max occurred (units hours) sda_coeff = specific dynamic action (SDA) coefficient (units %) tarr = temperature of arrhythmia (units degC), only measured during winter tests fhmax_peak = peak maximum heart rate (units beats per min), only measured during winter tests tpeak = temperature at which fhmax_peak occurred (units degC), only measured during winter tests ## Sharing/Access Information 1. Licenses/restrictions placed on the data: N/A 2. Links to other publicly accessible locations of the data: N/A 3. Was data derived from another source? No Climate change is intensifying extreme weather events, including marine heatwaves, which are prolonged periods of anomalously high sea surface temperature that pose a novel threat to aquatic animals. Tropical animals may be especially vulnerable to marine heatwaves because they are adapted to a narrow temperature range. If these animals cannot acclimate to marine heat waves, the extreme heat could impair their behavior and fitness. Here, we investigated how marine heatwave conditions affected the performance and thermal tolerance of a tropical predatory fish, arceye hawkfish (Paracirrhites arcatus), across two seasons in Mo'orea, French Polynesia. We found that the fish’s daily activities, including recovery from burst swimming and digestion, were more energetically costly in fish exposed to marine heatwave conditions across both seasons, while their aerobic capacity remained the same. Given their constrained energy budget, these rising costs associated with warming may impact how hawkfish prioritize activities. Additionally, hawkfish that were exposed to hotter temperatures exhibited cardiac plasticity by increasing their maximum heart rate but were still operating within a few degrees of their thermal limits. With more frequent and intense heatwaves, hawkfish, and other tropical fishes must rapidly acclimate, or they may suffer physiological consequences that alter their role in the ecosystem. Hawkfish (Paracirrhites arcatus) were collected in Mo'orea, French Polynesia during the Austral winter (2019) and Austral summer (2022). They were acclimated to one of five treatments (27, 28, 29, 31, or 33°C) for one week and tested for metabolic performance metrics, including maximum metabolic rate (MMR), standard metabolic rate (SMR), and costs of digestion (specific dynamic action, SDA) using custom-made respirometry chambers. A subset of fish was also tested for thermal tolerance using an acute cardiac thermal tolerance test. In addition, wild fish were also caught and tested for acute cardiac thermal tolerance. Metabolic data were processed in R and heart rate data were processed in LabChart. Please see the published manuscript for detailed methods. 

Abstract Climate change is affecting freshwater systems, leading to increased water temperatures, which is posing a threat to freshwater ecological communities. In the Nechako River, a water management program has been in place since the 1980s to maintain water temperatures at 20°C during the migration of Sockeye salmon. However, the program's effectiveness in mitigating the impacts of climate change on resident species like Chinook salmon's thermal exposure is uncertain. In this study, we utilised the CEQUEAU hydrological model and life stage-specific physiological data to evaluate the consequences of the current program on Chinook salmon's thermal exposure under two contrasting climate change and socio-economic scenarios (SSP2-4.5 and SSP5-8.5). The results indicate that the thermal exposure risk is projected to be above the optimal threshold for parr and adult life stages under both scenarios relative to the 1980s. These life stages could face an increase in thermal exposure ranging from up to 2 and 5 times by 2090s relative to the 1980s during the months they occurred under the SSP5-8.5 scenario, including when the program is active (July 20th to August 20th). Additionally, our study shows that climate change will result in a substantial rise in cumulative heat degree days, ranging from 1.9 to 5.8 times (2050s) and 2.9 to 12.9 times (2090s) in comparison to the 1980s under SSP5-8.5. Our study highlights the need for a holistic approach to review the current Nechako management plan and consider all species in the Nechako River system in the face of climate change.

<b>Abstract</b><br/><p>Climate change is causing large declines in many Pacific salmon populations. In particular, warm rivers are associated with high levels of premature mortality in migrating adults. The Fraser River watershed in British Columbia, Canada, supports some of the largest Chinook salmon (<em>Oncorhynchus tshawytscha</em>) runs in the world. However, the Fraser River is warming at a rate that threatens these populations at critical freshwater life stages. A growing body of literature suggests salmonids are locally adapted to their thermal migratory experience, and thus, population-specific thermal performance information can aid in management decisions. We compared the thermal performance of pre-spawning adult Chinook salmon from two populations, a coastal fall-run from the Chilliwack River (125 km cooler migration) and an interior summer-run from the Shuswap River (565 km warmer migration). We acutely exposed fish to temperatures reflecting current (12, 18°C) and future projected temperatures (21, 24°C) in the Fraser River and assessed survival, aerobic capacity (resting and maximum metabolic rates, absolute aerobic scope (AAS), muscle and ventricle citrate synthase), anaerobic capacity (muscle and ventricle lactate dehydrogenase), and recovery capacity (post-exercise metabolism, blood physiology, tissue lactate). Chilliwack Chinook salmon performed worse at high temperatures, indicated by elevated mortality, reduced breadth in AAS, enhanced plasma lactate and potassium levels, and elevated tissue lactate concentrations compared to Shuswap Chinook salmon. At water temperatures exceeding the upper pejus temperatures (T_pejus, defined here as 80% of maximum AAS) of Chilliwack (18.7°C) and Shuswap (20.2°C) Chinook salmon populations, physiological performance will decline and affect migration and survival to spawn. Our results reveal population differences in pre-spawning Chinook salmon performance across scales of biological organization at ecologically relevant temperatures. Given the rapid warming of rivers, we show that it is critical to consider the intra-specific variation in thermal physiology to assist in the conservation and management of Pacific salmon.</p> Dryad version number: 3 Version status: submitted Dryad curation status: Published Sharing link: https://datadryad.org/stash/share/oQgYTV4t2_8it7SXfHioEkKWgViUakIRZnwJ0CUMIag Storage size: 85271 Visibility: public <b>Methods</b><br /><div> <p>Please see the main manuscript for all information regarding data collection and analysis.</p> </div>