Non-invasive MRI Studies of Ventilatory and Cardiovascular Performance in Edible Crabs Cancer pagurus During Warming Under Elevated CO2 Levels

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 degrees C over 5 days) under control (470 mu atm) and high (1,350 mu atm) 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 (MO2), ventilation and cardiovascular performance. Crabs spent significantly more time in a low MO2 state (metabolic pause), when experiencing high CO2 conditions above 16 degrees C, compared to normocapnic warming. Heart rates leveled off beyond 18 degrees 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 degrees C. These results indicate constrained oxygen uptake at stable cardiovascular performance in a decapod crustacean.

Automated summary

This study investigated the impacts of warming on ventilation and hemolymph circulation in edible crabs under different CO2 levels, finding that high CO2 conditions led to more time spent in a low metabolic state and suppressed ventilation, while cardiac output continued to increase.