Future high CO2 in the intertidal may compromise adult barnacle Semibalanus balanoides survival and embryonic development rate

The effects Of CO2-induced acidification on survival, shell mineralogy, embryonic development and the timing of larval release were investigated in the intertidal barnacle Semibalanus balanoides using an intertidal microcosm system. Compared to that in the control (CO2 = 344 ppm, pH = 8.07), adult survival was 22% lower in the high-CO2 treatment (CO2 = 922 ppm, pH = 7.70) and significant changes in the mineral structure of the adult shell were observed. Embryonic development rate was significantly slower in the high-CO2 treatment than in the control but still resembled 'natural' rates seen in populations found in similar locations. There was an estimated 19 d delay in development under high-CO2 conditions, which resulted in a 60% reduction in the number of nauplii reaching hatching stage at the time when over 50%, of the control nauplii had hatched. We conclude that ocean acidification could potentially further compromise embryonic development in a species already stressed by temperature, which could in turn impact naupliar development and recruitment. S. balanoides, the adults of which live in a highly variable environment, has been shown to be detrimentally impacted by a chronic change in chemical conditions (pH lowered beyond the current range) over a crucial period in their life cycle. Under experimental high-CO2 conditions, some adults were able to survive and larvae were able to hatch. This may indicate that there is still potential for organisms to find suitable habitats and for populations to develop and survive.