Description: Low-salinity stress can severely affect the fitness of marine organisms. As desalination has been predicted for many coastal areas with ongoing climate change, it is crucial to gain more insight in mechanisms that constrain salinity acclimation ability. Low-salinity induced depletion of the organic osmolyte pool has been suggested to set a critical boundary in osmoconforming marine invertebrates. Whether inorganic ions also play a persistent role during low-salinity acclimation processes is currently inconclusive. We investigated the salinity tolerance of six marine invertebrate species following a four-week acclimation period around their low-salinity tolerance threshold. To obtain complete osmolyte budgets, we quantified organic and inorganic osmolytes and determined fitness proxies. Our experiments corroborated the importance of the organic osmolyte pool during low-salinity acclimation. Methylamines constituted a large portion of the organic osmolyte pool in molluscs, whereas echinoderms exclusively utilized free amino acids. Inorganic osmolytes were involved in long-term cellular osmoregulation in most species, thus are not just modulated with acute salinity stress. The organic osmolyte pool was not depleted at low salinities, whilst fitness was severely impacted. Instead, organic and inorganic osmolytes often stabilized at low-salinity. These findings suggest that low-salinity acclimation capacity cannot be simply predicted from organic osmolyte pool size. Rather, multiple parameters (i.e. osmolyte pools, net growth, water content and survival) are necessary to establish critical salinity ranges. However, a quantitative knowledge of cellular osmolyte systems is key to understand the evolution of euryhalinity and to characterize targets of selection during rapid adaptation to ongoing desalination.

Description: Cancer pagurus from the North Sea were exposued to acute, step-wise warming under two levels of CO2. The exposure to either normocapnic (450 µatm CO2) or hypercapnic (1350 µatm CO2) conditions was randomized on a temperature ramp between 12 and 20°C. Steps of constant temperatures were 10 h every two °C (12, 14, 16, 18, 20°C). Seawater chemistry (temperature, salinity, ph, PCO2) was analysed at 12 and 20°C. pH is given on the free scale and used for subsequent calculation of totalk alkalinity (TA), bicarbonate concentration and dissolved inorganic carbon (DIC). Physiological parameters were recorded over the course of a temperature ramp: Whole-animal metabolic rate (MO2) via flow-through respirometry. Heart rates (HR) via infrared photoplethysmography (IR-PPG). The integral of the raw signal of the plethysmogrpah served as a proxy for cardiac stroke volume (SV). Is was normalized to a control SV of 0.2 mL, based on literature references. The product of HR and SV equals cardiac output (CO). The difference between logtime_MO2 and logtime is that MO2 (whole-animal metabolic rate) were sometimes recorded with an inconsistent temporal delay compared to the other parameters. For accurate correlation of the data, readers are kindly asked to use the correct logtimes for each parameter (i.e. "logtime_MO2" for "MO2" and "logtime" for the others). In a parallel experiment, ventilatory water flow in the excurrent channel of the gill chambers, as well as haemolymph flow in the arteria sternalis and branchial veins was determined via phase-contrast magnetic resonance imaging (MRI). The lateral contractility of the heart was determined from self-gated cardiac MRI movies at 12 and 20°C during diastole and systole.

Description: Dynamic in vivo 31P-NMR spectroscopy in combination with Magnetic Resonance Imaging (MRI) was used to study muscle bioenergetics of boreal and Arctic scallops (Pecten maximus and Chlamys islandica) to test the hypothesis that future Ocean Warming and Acidification (OWA) will impair the performance of marine invertebrates.

Description: Robust estimates of marine species vulnerability to ongoing climate change require realistic stressor experiments. Here, we subjected an important coastal predator, the sea star Asterias rubens, to projected warming and ocean acidification over an annual seasonal cycle. Warming and, less so, acidification, had strongly season-specific impacts on animal energy budgets. Specifically, simulated future summer temperatures caused 〉95% sea star mortality, reduced feeding rate and body mass loss. Additional acute experiments demonstrated that respiratory oxygen flux was preferentially directed to support high summer metabolism at the expense of feeding-related processes. Using 15 years of field temperature data and end of century warming projections, we estimate that potentially lethal summer heat waves will occur in 20% of future years. Our study demonstrates the importance of assessing stress responses along seasonal thermal cycles and the high selective force that future summer heat waves likely can exert on coastal marine animal populations.

Description: Robust estimates of marine species vulnerability to ongoing climate change require realistic stressor experiments. Here, we subjected an important coastal predator, the sea star Asterias rubens, to projected warming and ocean acidification over an annual seasonal cycle. Warming and, less so, acidification, had strongly season-specific impacts on animal energy budgets. Specifically, simulated future summer temperatures caused 〉95% sea star mortality, reduced feeding rate and body mass loss. Additional acute experiments demonstrated that respiratory oxygen flux was preferentially directed to support high summer metabolism at the expense of feeding-related processes. Using 15 years of field temperature data and end of century warming projections, we estimate that potentially lethal summer heat waves will occur in 20% of future years. Our study demonstrates the importance of assessing stress responses along seasonal thermal cycles and the high selective force that future summer heat waves likely can exert on coastal marine animal populations.

Description: Robust estimates of marine species vulnerability to ongoing climate change require realistic stressor experiments. Here, we subjected an important coastal predator, the sea star Asterias rubens, to projected warming and ocean acidification over an annual seasonal cycle. Warming and, less so, acidification, had strongly season-specific impacts on animal energy budgets. Specifically, simulated future summer temperatures caused 〉95% sea star mortality, reduced feeding rate and body mass loss. Additional acute experiments demonstrated that respiratory oxygen flux was preferentially directed to support high summer metabolism at the expense of feeding-related processes. Using 15 years of field temperature data and end of century warming projections, we estimate that potentially lethal summer heat waves will occur in 20% of future years. Our study demonstrates the importance of assessing stress responses along seasonal thermal cycles and the high selective force that future summer heat waves likely can exert on coastal marine animal populations.

Description: Robust estimates of marine species vulnerability to ongoing climate change require realistic stressor experiments. Here, we subjected an important coastal predator, the sea star Asterias rubens, to projected warming and ocean acidification over an annual seasonal cycle. Warming and, less so, acidification, had strongly season-specific impacts on animal energy budgets. Specifically, simulated future summer temperatures caused 〉95% sea star mortality, reduced feeding rate and body mass loss. Additional acute experiments demonstrated that respiratory oxygen flux was preferentially directed to support high summer metabolism at the expense of feeding-related processes. Using 15 years of field temperature data and end of century warming projections, we estimate that potentially lethal summer heat waves will occur in 20% of future years. Our study demonstrates the importance of assessing stress responses along seasonal thermal cycles and the high selective force that future summer heat waves likely can exert on coastal marine animal populations.