AbstractAnimals and their neuronal circuits must maintain function despite significant environmental fluctuations. The crab, Cancer borealis, experiences daily changes in ocean temperature and pH. Here, we describe the effects of extreme changes in extracellular pH – from pH 5.5 to 10.4 – on two central pattern generating networks, the stomatogastric and cardiac ganglia of C. borealis. Given that the physiological properties of ion channels are known to be sensitive to pH within the range tested, it is surprising that these rhythms generally remained robust from pH 6.1 to pH 8.8. Unexpectedly, the stomatogastric ganglion was more sensitive to acid while the cardiac ganglion was more sensitive to base. Considerable animal-to-animal variability was likely a consequence of similar network performance arising from variable sets of underlying conductances. Together, these results illustrate the potential difficulty in generalizing the effects of environmental perturbation across circuits, even within the same animal.AbbreviationsSTGstomatogastric ganglionCGcardiac ganglionCPGcentral pattern generatorABAnterior BursterPDPyloric DilatorLPLateral PyloricPYPyloricSCSmall CellLCLarge Celllvnlateral ventricular nerveANOVAanalysis of variancePTXpicrotoxinIPSPinhibitory post-synaptic potentialLGLateral GastricMGMedial GastricLPGLateral Posterior GastricGMGastric MillDGDorsal GastricAMAnterior MedianInt1Interneuron 1mvnmedial ventricular nervedgndorsal gastric nervelgnlateral gastric nerveioninferior oesophageal nerveICInferior CardiacVDVentricular DilatorMCN1Modulatory Commissural Neuron 1VCNVentral Cardiac NeuronCPN2Commissural Projection Neuron 2CoGcommissural ganglionKDEkernel density estimateIQRinterquartile rangeCIconfidence interval