Relationship between CO2-driven changes in extracellular acid–base balance and cellular immune response in two polar echinoderm species

Anthropogenic CO2 emissions are acidifying the world's oceans. A growing body of evidence demonstrates that ocean acidification can impact survival, growth, development and physiology of marine invertebrates. However, little is known on the impact of elevated pCO2 on immune-response. Here we investigate the impact of short-term (5–7 days) exposure to elevated pCO2 (1275 μatm compared to 350 μatm in the control) on extracellular pH (pHe) and cellular immune response in two polar echinoderm species, the green sea urchin Strongylocentrotus droebachiensis and the seastar Leptasterias polaris. Both species experienced extracellular acidosis following short term exposure to elevated pCO2. While this acidosis remained uncompensated within 7 days for L. polaris, pHe was fully compensated after 5 days for S. droebachiensis. For both species, coelomic fluid acidosis was associated with an increase in total coelomocyte number and a reduction in vibratile cells in S. droebachiensis. A relationship between pHe and phagocyte numbers was observed in S. droebachiensis suggesting a direct link between pHe and cellular immune-response. Further studies would require the coordinated effort of ecologists and immunologists to understand the role of elevated pCO2 on the host–pathogen interactions that are involved in the stability of ecosystems.

► Sea urchins are able to fully compensate pHe for elevated pCO2 within 5 days.
► Sea stars are not.
► There is a link between pHe and cellular immune response.
► There is no evidence for increased sensitivity to elevated pCO2 in Polar species.
► To elevated pCO2 in Polar species compared to Temperate/Tropical ones.