Distribution of sea urchins living near shallow water CO2 vents is dependent upon species acid-base and ion-regulatory abilities

► Arbacia lixula occurs at greater density in high pCO2 areas of Vulcano's CO2 vents. ► Instead Paracentrotus lividus occurs at lower density nearer the CO2 vents. ► Sea urchins partly regulate coelomic fluid acid-base and ionic status in high pCO2. ► A. lixula overall shows a greater homeostatic capacity when compared to P. lividus. ► Species distribution under high pCO2 appears homeostasis capacity-dependent.