extremely significantP<0.001
The statistical analysis of mean difference of blue hole diameters from different H 2 O 2 showed that the increase of hole diameters is extremely significant (P<0.001) with the increase of H 2 O 2 from 0 to 20 mM, but not significant (P>0.05) with the increase of H 2 O 2 from 20 mM to 30 mM ( Table S1 ).