Negative effects of ocean acidification on two crustose coralline species using genetically homogeneous samples

• We evaluated ocean acidification effects on crustose coralline algae in coral reefs.
• We used genetically homogenous samples in order to eliminate species misidentification.
• Growth inhibition by high pCO2 is species specific.
• The decreasing trend of calcified cell walls was not different between species.
• The solubility or density of calcite is related to species-level susceptibility.

We evaluated acidification effects on two crustose coralline algal species common to Pacific coral reefs, Lithophyllum kotschyanum and Hydrolithon samoense. We used genetically homogeneous samples of both species to eliminate misidentification of species. The growth rates and percent calcification of the walls of the epithallial cells (thallus surface cells) of both species decreased with increasing pCO2. However, elevated pCO2 more strongly inhibited the growth of L. kotschyanum versus H. samoense. The trend of decreasing percent calcification of the cell wall did not differ between these species, although intercellular calcification of the epithallial cells in L. kotschyanum was apparently reduced at elevated pCO2, a result that might indicate that there are differences in the solubility or density of the calcite skeletons of these two species. These results can provide knowledge fundamental to future studies of the physiological and genetic mechanisms that underlie the response of crustose coralline algae to environmental stresses.