Usage of Internal Heart Rate Bio-Loggers in Arctic Fish

By anthropogenic cause, even the most optimistic climate models (i.e. SSP1–RCP2.6) predict the Arctic system to heat up by more than 4°C until the year 2100, relative to the present. For ectothermic fishes, energy demand is fundamentally determined by temperature. As energy is physiologically limiting, their means to cope with climate change are limited. Therefore, understanding the impact of environmental changes on bioenergetics is imperative for the management of marine ecosystems. In recent years, the species-specific relevance of heart rate (ƒH) as a proxy for energy expenditure has been highlighted by the scientific community. The advent of bio-logging sciences has enabled ƒH observation in free swimming individuals. For Arctic fishes, however, harsh environmental conditions have restricted the pursue of ƒH bio- logging so far. To bridge this knowledge gap, we partnered with Star-Oddi, who developed a novel, internal ƒH and temperature bio-logger, calibrated for temperatures down to –5°C. In the present study, this bio-logger was implanted in the cold-adapted Arctic specialist polar cod (Boreogadus saida) and the ƒH bio-logging methodology was progressed in simulation of the ecologically relevant temperature range (i.e. 0 to 8°C) and free-roaming exercise (i.e. critical swimming speed (Ucrit) tests). Bio-logger positioning with exterior-facing electrodes and increase in sampling frequency from 100 Hz to 125 Hz improved electrocardiogram (ECG) quality significantly (p < 0.0001 and p = 0.02, respectively), due to decreased electromyogram (EMG) noise penetration and more distinct mapping of processed ECG characteristics. Under these settings, in the range of 0 to 4°C, in relation to 1180 manually calculated ECG traces, 80 ± 1.5% of on-board processed ƒH measurements displayed highest quality (i.e. QI = 0) with a confidence of ∆ƒH = 0.45 ± 0.56 bpm. Furthermore, 53 ± 5.5% of measurements displayed highest quality homogenously across swimming velocities up to Ucrit. Hence, present ƒH bio-logging methodology was validated to be highly robust in response to simulated Arctic conditions. Species-specifically for polar cod, standard metabolic rate (SMR) of bio-logged individuals at 0 ± 0.5°C amounted to 0.38 μmol/g/h. Therewith, it was lower than the previously determined 0.44 μmol/g/h for untagged conspecifics at 2.5 ± 1°C, indicating that present measurements were representative, especially given expected deviation from Q10 rules due to oxygen demands of cold adaptations. Polar cod ƒH was highly sensitive to, and consequently significantly impacted by, both temperature and swimming velocity (each with p < 0.0001). Remarkably, ƒH at Ucrit mirrored ƒHmax values previously obtained at the same temperatures by humoral injections, supporting causal relationship of ƒHmax and consequent performance limitations. Further, incremental ƒH Q10 values decreased from 2.54 ± 0.76 at 0–4°C to 2.00 ± 0.50 at 6°C and 1.73 ± 0.74 at 8°C. Hence, polar cod ƒH started failing to scale with temperatures past 4– 6°C, which in accordance with previously described temperature ranges and susceptibilities, potentially indicated the transition to passive thermal tolerance. Overall, oxygen consumption was significantly correlated to ƒH with a spearman rank correlation coefficient rho = 0.42. Lastly, the interaction of swimming velocity and temperature did not significantly impact MO2 (p = 0.71) and the relationship’s slopes displayed high similarity between 0, 2, and 8°C. In conclusion, the contribution of ƒH in regulation, and ultimately limitation, of oxygen supply in response to temperature- and performance-related energy demand, was determined as highly probable. Therefore, the potential of ƒH as a proxy for energy expenditure in polar cod was highlighted over the course of the present research

Cold Fish Don’t Miss a Beat: Internal Heart Rate Bio-logging of Polar Cod (Boreogadus saida)

In this study, we adapted Star-Oddi micro-HRT (G2) bio-loggers for improved function in the cold-adapted Arctic key species Polar cod (B. saida) that generally displays a very low heart rate (ƒH) of 8bpm. To integrate ƒH data with oxygen consumption rates (MO2), we conducted critical swim speed (Ucrit) tests in a swim-tunnel respirometer within the ecologically relevant temperature range of 0–8°C. A significant correlation (p < 0.01) of observed cardiorespiratory parameters indicated primary dependency of ƒH and MO2 during acute warming, suggesting a species-specific potential of ƒH as a proxy for energy expenditure. Despite present Ucrit (2.3 ± 0.3 BL/s) being 20% lower than in untagged conspecifics at similar temperature, maximum metabolic rates were 35% higher for bio-logger-bearing individuals. Apparent excess potential to increase MO2 suggests that polar cod’s performance limitations are not dictated by the absolute capacity of oxygen supply. Hence, alternative explanations determining Ucrit, such as behavioral termination of swimming trials to save energy, or potential limitations in ATP supply to the muscle, are discussed. Heart rate was significantly impacted by both temperature and swimming velocity (p < 0.0001, respectively). Past the optimal temperature range of polar cod (2.8–4.4°C), heart rate ceased to increase, with incremental Q10 values levelling off from 2.63±0.43 at 0–2°C, to 1.73±0.74 at 6–8°C. Consequently, potential impacts of insufficient heart rate scaling with acute temperature rise are discussed in the light of projected Arctic warming

Oxygen consumption of F0 and F1 larval and juvenile European seabass Dicentrarchus labrax in resonse to ocean acidification and warming

Ongoing climate change is leading to warmer and more acidic oceans. The future distribution of fish within the oceans depends on their capacity to adapt to these new environments. Only few studies have examined the effects of ocean acidification (OA) and warming (OW) on the metabolism of long-lived fish over successive generations. We therefore aimed to investigate the effect of OA on larval and juvenile growth and metabolism on two successive generations of European sea bass (Dicentrarchus labrax L.) as well as the effect of OAW on larval and juvenile growth and metabolism of the second generation. European sea bass is a large economically important fish species with a long generation time. F0 larvae were produced at the aquaculture facility Aquastream (Ploemeur-Lorient, France) and obtained at 2 days post-hatch (dph). From 2 dph F0 larvae were reared in the laboratory in two PCO2 conditions (ambient and Δ1000). Larval rearing was performed in a temperature controlled room and water temperatures were fixed to 19°C in F0. In juveniles and adults, water temperatures of F0 sea bass were adjusted to ambient temperature in the Bay of Brest during summer (up to 19°C), but were kept constant at 15 and 12°C for juveniles and adults, respectively, when ambient temperature decreased below these values. F1 embryos were obtained by artificial reproduction of F0 broodstock fish. Fertilized eggs were incubated at 15°C and at the same PCO2 conditions as respective F0. Division of F1 larvae from egg rearing tanks into experimental tanks took place at 2 dph. F1 larvae were reared in four OAW conditions: two temperatures (cold and warm life condition, C and W) and two PCO2 conditions (ambient and Δ1000). Larval rearing was performed in a temperature controlled room and water temperatures were fixed to 15 and 20°C for C and W larvae, respectively. In juveniles, water temperatures of F1 sea bass were adjusted to ambient temperature in the Bay of Brest during summer (up to 19°C), but were kept constant at 15°C when ambient temperature decreased below these values. F1-W was always 5°C warmer than the F1-C treatment. OAW conditions for F0 and F1 rearing were chosen to follow the predictions of the IPCC for the next 130 years: ΔT = 5°C and ΔPCO2 = 1000 µatm, following RCP 8.5. We analysed larval and juvenile growth in F0 and F1. Larval routine metabolic rates (RMR, in F1), juvenile standard metabolic rates (SMR, in F0 and F1) and juvenile critical oxygen concentrations (PO2crit, in F0 and F1) were obtained on individuals via intermittent flow-respirometry. Measurements were conducted at the rearing conditions of the respective larva or juvenile. Fish were fasted for 3h and 48-72h for larvae and juveniles, respectively. After the respirometry trial, larvae were photographed to measure there body length and frozen until measurement of dry mass. Juveniles body length and wet mass was directly determined with calipers and a balance

Seawater carbonate chemistry and respiration and growth rates of F0 and F1 larval and juvenile European seabass Dicentrarchus labrax

European sea bass (Dicentrarchus labrax) is a large, economically important fish species with a long generation time whose long-term resilience to ocean acidification (OA) and warming (OW) is not clear. We incubated sea bass from Brittany (France) for two generations (>5 years in total) under ambient and predicted OA conditions (PCO2: 650 and 1700 µatm) crossed with ambient and predicted ocean OW conditions in F1 (temperature: 15-18°C and 20-23°C) to investigate the effects of climate change on larval and juvenile growth and metabolic rate. We found that in F1, OA as single stressor at ambient temperature did not affect larval or juvenile growth and OW increased developmental time and growth rates, but OAW decreased larval size at metamorphosis. Larval routine and juvenile standard metabolic rates were significantly lower in cold compared to warm conditioned fish and also lower in F0 compared to F1 fish. We did not find any effect of OA as a single stressor on metabolic rates. Juvenile PO2crit was not affected by OA or OAW in both generations. We discuss the potential underlying mechanisms resulting in the resilience of F0 and F1 larvae and juveniles to OA and in the beneficial effects of OW on F1 larval growth and metabolic rate, but on the other hand in the vulnerability of F1, but not F0 larvae to OAW. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures

Experimental conditions for respiration and growth studies of F0 and F1 larval and juvenile European seabass Dicentrarchus labrax

Water parameters in the 2 years before spawning of F0 (08.02.2016-06.03.2018) and during larval and juvenile phase of F1: Larval period until 17.05.2018 (48 dph, 900 dd) and 01.06.2018 (63 dph, ~900 dd) for warm and cold life condition respectively, for the juveniles until 28.09.2018 (180 dph, ~4000 dd) and 12.02.2019 (319 dph, ~5100 dd) for warm and cold conditioned fish respectively. Means ± s.e. over all replicate tanks per condition. Temperature (Temp.), pH (free scale), salinity, oxygen and total alkalinity (TA) were measured weekly in F1 and monthly in F0; sea water (SW) measurements were conducted in 2017 and 2018. Water parameters during larval and early juvenile phase of F0: Larval period until (45 dph, 900 dd, 06.12.2013), early juveniles until 1.5 years. Means ± s.e.m. over all measurements per condition (triplicate tanks in larvae, single tanks in juveniles). Temperature (Temp.) and pH (NBS scale) were measured daily. pH (total scale), salinity, phosphate, silicate and total alkalinity (TA) were measured once at the beginning and once at the end of the larval phase and 9 times during juvenile phase; PCO2 was calculated with CO2sys; A–Ambient PCO2, D1000 –ambient + 1000 µatm CO2, L – Larvae, J – Juveniles

Effects of ocean acidification over successive generations decrease resilience of larval European sea bass to ocean acidification and warming but juveniles could benefit from higher temperatures in the NE Atlantic

European sea bass (Dicentrarchus labrax) is a large, economically important fish species with a long generation time whose long-term resilience to ocean acidification (OA) and warming (OW) is not clear. We incubated sea bass from Brittany (France) for two generations (>5 years in total) under ambient and predicted OA conditions (PCO2: 650 and 1700 µatm) crossed with ambient and predicted ocean OW conditions in F1 (temperature: 15-18°C and 20-23°C) to investigate the effects of climate change on larval and juvenile growth and metabolic rate. We found that in F1, OA as single stressor at ambient temperature did not affect larval or juvenile growth and OW increased developmental time and growth rates, but OAW decreased larval size at metamorphosis. Larval routine and juvenile standard metabolic rates were significantly lower in cold compared to warm conditioned fish and also lower in F0 compared to F1 fish. We did not find any effect of OA as a single stressor on metabolic rates. Juvenile PO2crit was not affected by OA or OAW in both generations. We discuss the potential underlying mechanisms resulting in the resilience of F0 and F1 larvae and juveniles to OA and in the beneficial effects of OW on F1 larval growth and metabolic rate, but on the other hand in the vulnerability of F1, but not F0 larvae to OAW. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures

Respiration and growth rates of F0 and F1 larval and juvenile European seabass Dicentrarchus labrax in response to ocean acidification and warming

Ongoing climate change is leading to warmer and more acidic oceans. The future distribution of fish within the oceans depends on their capacity to adapt to these new environments. Only few studies have examined the effects of ocean acidification (OA) and warming (OW) on the metabolism of long-lived fish over successive generations. We therefore aimed to investigate the effect of OA on larval and juvenile growth and metabolism on two successive generations of European sea bass (Dicentrarchus labrax L.) as well as the effect of OAW on larval and juvenile growth and metabolism of the second generation. European sea bass is a large economically important fish species with a long generation time. F0 larvae were produced at the aquaculture facility Aquastream (Ploemeur-Lorient, France) and obtained at 2 days post-hatch (dph). From 2 dph F0 larvae were reared in the laboratory in two PCO2 conditions (ambient and Δ1000). Larval rearing was performed in a temperature controlled room and water temperatures were fixed to 19°C in F0. In juveniles and adults, water temperatures of F0 sea bass were adjusted to ambient temperature in the Bay of Brest during summer (up to 19°C), but were kept constant at 15 and 12°C for juveniles and adults, respectively, when ambient temperature decreased below these values. F1 embryos were obtained by artificial reproduction of F0 broodstock fish. Fertilized eggs were incubated at 15°C and at the same PCO2 conditions as respective F0. Division of F1 larvae from egg rearing tanks into experimental tanks took place at 2 dph. F1 larvae were reared in four OAW conditions: two temperatures (cold and warm life condition, C and W) and two PCO2 conditions (ambient and Δ1000). Larval rearing was performed in a temperature controlled room and water temperatures were fixed to 15 and 20°C for C and W larvae, respectively. In juveniles, water temperatures of F1 sea bass were adjusted to ambient temperature in the Bay of Brest during summer (up to 19°C), but were kept constant at 15°C when ambient temperature decreased below these values. F1-W was always 5°C warmer than the F1-C treatment. OAW conditions for F0 and F1 rearing were chosen to follow the predictions of the IPCC for the next 130 years: ΔT = 5°C and ΔPCO2 = 1000 µatm, following RCP 8.5. We analysed larval and juvenile growth in F0 and F1. Larval routine metabolic rates (RMR, in F1), juvenile standard metabolic rates (SMR, in F0 and F1) and juvenile critical oxygen concentrations (PO2crit, in F0 and F1) were obtained on individuals via intermittent flow-respirometry. Measurements were conducted at the rearing conditions of the respective larva or juvenile. Fish were fasted for 3h and 48-72h for larvae and juveniles, respectively. After the respirometry trial, larvae were photographed to measure there body length and frozen until measurement of dry mass. Juveniles body length and wet mass was directly determined with calipers and a balance

Growth rates of F0 and F1 larval and juvenile European seabass Dicentrarchus labrax in resonse to ocean acidification and warming

Ongoing climate change is leading to warmer and more acidic oceans. The future distribution of fish within the oceans depends on their capacity to adapt to these new environments. Only few studies have examined the effects of ocean acidification (OA) and warming (OW) on the metabolism of long-lived fish over successive generations. We therefore aimed to investigate the effect of OA on larval and juvenile growth and metabolism on two successive generations of European sea bass (Dicentrarchus labrax L.) as well as the effect of OAW on larval and juvenile growth and metabolism of the second generation. European sea bass is a large economically important fish species with a long generation time. F0 larvae were produced at the aquaculture facility Aquastream (Ploemeur-Lorient, France) and obtained at 2 days post-hatch (dph). From 2 dph F0 larvae were reared in the laboratory in two PCO2 conditions (ambient and Δ1000). Larval rearing was performed in a temperature controlled room and water temperatures were fixed to 19°C in F0. In juveniles and adults, water temperatures of F0 sea bass were adjusted to ambient temperature in the Bay of Brest during summer (up to 19°C), but were kept constant at 15 and 12°C for juveniles and adults, respectively, when ambient temperature decreased below these values. F1 embryos were obtained by artificial reproduction of F0 broodstock fish. Fertilized eggs were incubated at 15°C and at the same PCO2 conditions as respective F0. Division of F1 larvae from egg rearing tanks into experimental tanks took place at 2 dph. F1 larvae were reared in four OAW conditions: two temperatures (cold and warm life condition, C and W) and two PCO2 conditions (ambient and Δ1000). Larval rearing was performed in a temperature controlled room and water temperatures were fixed to 15 and 20°C for C and W larvae, respectively. In juveniles, water temperatures of F1 sea bass were adjusted to ambient temperature in the Bay of Brest during summer (up to 19°C), but were kept constant at 15°C when ambient temperature decreased below these values. F1-W was always 5°C warmer than the F1-C treatment. OAW conditions for F0 and F1 rearing were chosen to follow the predictions of the IPCC for the next 130 years: ΔT = 5°C and ΔPCO2 = 1000 µatm, following RCP 8.5. We analysed larval and juvenile growth in F0 and F1. Larval routine metabolic rates (RMR, in F1), juvenile standard metabolic rates (SMR, in F0 and F1) and juvenile critical oxygen concentrations (PO2crit, in F0 and F1) were obtained on individuals via intermittent flow-respirometry. Measurements were conducted at the rearing conditions of the respective larva or juvenile. Fish were fasted for 3h and 48-72h for larvae and juveniles, respectively. After the respirometry trial, larvae were photographed to measure there body length and frozen until measurement of dry mass. Juveniles body length and wet mass was directly determined with calipers and a balance