Impact of anthropogenic ocean acidification on thermal tolerance of the spider crab <i>Hyas araneus</i>

Future scenarios for the oceans project combined developments of CO₂ accumulation and global warming and their impact on marine ecosystems. The synergistic impact of both factors was addressed by studying the effect of elevated CO₂ concentrations on thermal tolerance of the cold-eurythermal spider crab <i>Hyas araneus</i> from the population around Helgoland. Here ambient temperatures characterize the southernmost distribution limit of this species. Animals were exposed to present day normocapnia (380 ppm CO₂), CO₂ levels expected towards 2100 (710 ppm) and beyond (3000 ppm). Heart rate and haemolymph PO₂ (P_eO₂) were measured during progressive short term cooling from 10 to 0&deg;C and during warming from 10 to 25&deg;C. An increase of P_eO₂ occurred during cooling, the highest values being reached at 0&deg;C under all three CO₂ levels. Heart rate increased during warming until a critical temperature (<i>T_c</i>) was reached. The putative <i>T_c</i> under normocapnia was presumably &gt;25&deg;C, from where it fell to 23.5&deg;C under 710 ppm and then 21.1&deg;C under 3000 ppm. At the same time, thermal sensitivity, as seen in the <i>Q₁₀</i> values of heart rate, rose with increasing CO₂ concentration in the warmth. Our results suggest a narrowing of the thermal window of <i>Hyas araneus</i> under moderate increases in CO₂ levels by exacerbation of the heat or cold induced oxygen and capacity limitation of thermal tolerance

Listening In on the Past: What Can Otolith δ18O Values Really Tell Us about the Environmental History of Fishes?

Oxygen isotope ratios from fish otoliths are used to discriminate marine stocks and reconstruct past climate, assuming that variations in otolith δ18O values closely reflect differences in temperature history of fish when accounting for salinity induced variability in water δ18O. To investigate this, we exploited the environmental and migratory data gathered from a decade using archival tags to study the behaviour of adult plaice (Pleuronectes platessa L.) in the North Sea. Based on the tag-derived monthly distributions of the fish and corresponding temperature and salinity estimates modelled across three consecutive years, we first predicted annual otolith δ18O values for three geographically discrete offshore sub-stocks, using three alternative plausible scenarios for otolith growth. Comparison of predicted vs. measured annual δ18O values demonstrated >96% correct prediction of sub-stock membership, irrespective of the otolith growth scenario. Pronounced inter-stock differences in δ18O values, notably in summer, provide a robust marker for reconstructing broad-scale plaice distribution in the North Sea. However, although largely congruent, measured and predicted annual δ18O values of did not fully match. Small, but consistent, offsets were also observed between individual high-resolution otolith δ18O values measured during tag recording time and corresponding δ18O predictions using concomitant tag-recorded temperatures and location-specific salinity estimates. The nature of the shifts differed among sub-stocks, suggesting specific vital effects linked to variation in physiological response to temperature. Therefore, although otolith δ18O in free-ranging fish largely reflects environmental temperature and salinity, we counsel prudence when interpreting otolith δ18O data for stock discrimination or temperature reconstruction until the mechanisms underpinning otolith δ18O signature acquisition, and associated variation, are clarified

How do we best synergise climate mitigation actions to co-benefit biodiversity?

Acknowledgements We thank Yuka Otsuki Estrada for help in designing and producing the table, and all other authors of the IPBES-IPCC report on the scientific outcome of the IPBES-IPCC co-sponsored workshop on biodiversity and climate change (Pörtner et al., 2021) for cross-cutting discussions during preparation of this analysis. Although this paper is based on the report of the IPBES-IPCC co882 sponsored workshop, the views expressed here represent the individual views of the authors. We would also like to thank the scientific steering committee of the IPBES-IPCC co-sponsored workshop, review editors, the IPCC and IPBES Secretariat, especially Anne Larigauderie, and Technical Support Units. In memory of our friend and co-author, Bob Scholes, who sadly died during the preparation of this synthesis, and who will be sorely missed by all.Peer reviewedPostprin

Impact of ocean acidification on thermal tolerance and acid–base regulation of Mytilus edulis from the White Sea

Ocean warming and acidification are two important environmental drivers affecting marine organisms. Organisms living at high latitudes might be especially threatened in near future, as current environmental changes are larger and occur faster. Therefore, we investigated the effect of hypercapnia on thermal tolerance and physiological performance of sub-Arctic Mytilus edulis from the White Sea. Mussels were exposed (2 weeks) to 390 µatm (control) and 1,120 µatm CO2 (year 2100) before respiration rate (MO2), anaerobic metabolite (succinate) level, haemolymph acid-base status, and intracellular pH (pHi) were determined during acute warming (10-28°C, 3°C over night). In normocapnic mussels, warming induced MO2 to rise exponentially until it levelled off beyond a breakpoint temperature of 20.5°C. Concurrently, haemolymph PCO2 rose significantly >19°C followed by a decrease in PO2 indicating the pejus temperature (TP, onset of thermal limitation). Succinate started to accumulate at 28°C under normocapnia defining the critical temperature (TC). pHi was maintained during warming until it dropped at 28°C, in line with the concomitant transition to anaerobiosis. At acclimation temperature, CO2 had only a minor impact. During warming, MO2 was stimulated by CO2 resulting in an elevated breakpoint of 25.8°C. Nevertheless, alterations in haemolymph gases (>16°C) and the concomitant changes of pHi and succinate level (25°C) occurred at lower temperature under hypercapnia versus normocapnia indicating a downward shift of both thermal limits TP and TC by CO2. Compared to temperate conspecifics, sub-Arctic mussels showed an enhanced thermal sensitivity, exacerbated further by hypercapnia, indicating their potential vulnerability to environmental changes projected for 2100

Can Oxygen Set Thermal Limits in an Insect and Drive Gigantism?

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