Abstract
The thermal tolerance of marine decapod crustacea is defined through their capacities for oxygen uptake and distribution. High ambient CO2 levels were previously shown to reduce hemolymph oxygen levels at enhanced cardiac performance during warming. This study investigated the impacts of warming under two CO2 levels on ventilation and hemolymph circulation in edible crabs Cancer pagurus. It also highlights changes in the ventilatory and cardiac pauses displayed by Decapoda under routine metabolism. Animals were exposed to step-wise, sub-critical warming (12–20°C over 5 days) under control (470 μatm) and high (1,350 μatm) water PCO2. Flow-through respirometry was combined with magnetic resonance imaging and infra-red photoplethysmography to allow for simultaneous, non-invasive measurements of metabolic rates (), ventilation and cardiovascular performance. Crabs spent significantly more time in a low state (metabolic pause), when experiencing high CO2 conditions above 16°C, compared to normocapnic warming. Heart rates leveled off beyond 18°C at any CO2 level. Cardiac output continued to increase with high-CO2-warming, due to elevated cardiac stroke volumes. Consequently, temperature-dependent branchial hemolymph flow remained unaffected by CO2. Instead, a suppressing effect of CO2 on ventilation was found beyond 16°C. These results indicate constrained oxygen uptake at stable cardiovascular performance in a decapod crustacean.Cancer pagurus: urn:lsid:zoobank.org:act:B750F89A-84B5-448B-8D80-EBD724A1C9D4
Highlights
Edible crabs, Cancer pagurus, are abundant in the North Sea, which has been identified as a regional hot spot for global warming (Hobday and Pecl, 2014)
Total alkalinity (TA) and dissolved inorganic carbon (DIC) were the most variable components of the carbonate system between all groups, but changes were within 400 μmol kg−1 (
High-CO2conditions resulted in pHw, [HCO3−]w, TA, and DIC values were significantly different between magnetic resonance imaging (MRI) and infrared photoplethysmography (IR-PPG) experiments; still, absolute differences were not larger than between temperature treatments and considered negligible
Summary
Cancer pagurus, are abundant in the North Sea, which has been identified as a regional hot spot for global warming (Hobday and Pecl, 2014). Thermal tolerance in marine crustacea has been linked to hemolymph oxygen levels (PeO2), which are set by the capacities for oxygen uptake, delivery, and demand (Frederich et al, 2000; Frederich and Pörtner, 2000). PeO2 is maximal in the optimum temperature range: for C. pagurus, this maximum was found around 10–12°C (Metzger et al, 2007). Thermal limitation sets in when temperature-dependent oxygen demand in the tissues exceeds the oxygen supply via the cardiorespiratory system. Warming causes an increase in maximum heart rates and ventilation rates, but beyond Tp, ventilatory and cardiac limitations have been recorded: ventilation failed to increase with temperature in spider crabs Maja squinado. Heart rates continue to increase with temperature beyond Tp, but at a much lesser incline than below Tp (Frederich and Pörtner, 2000)
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