UKOA Benthic consortium study of acid-base and ion-regulatory abilities of sea urchins near shallow CO2 vents.

Only two echinoid species are common around the shallow water CO2 vents of Vulcano Island; the black sea urchin, Arbacia lixula and the purple sea urchin, Paracentrotus lividus. However, whilst the density of P. lividus decrease closer to the vents, the density of A. lixula increases. To determine what drives the differences in distribution of the two species, we conducted in situ transplantation and field-based laboratory exposures to different pCO2/pH regimes. As extracellular homeostasis is important in determining species' ability to cope with elevated CO2, we investigated acid-base and ion regulatory responses. Our results confirm that sea urchins have some ability to regulate their extracellular fluid under elevated pCO2. Furthermore, we show that even in closely-related taxa subtle divergent physiological capabilities underlie differences in taxa distribution around the CO2 vent. Thus differences in the eco-physiology of individual species (as with the sea urchins in this study) will likely play an important role in defining the ability of assemblages to cope with elevated pCO2/ low pH. It is likely that such differences will be due to changes in energy budgets, with follow-on constrains on species future abundance and distribution.