Variation in the experimental conditions.

Values for the carbonate system parameters were calculated using CO2SYS with temperature, salinity, total alkalinity (TA) and pHNBS as input parameters (n = 3). Additionally, the Biological Oxygen Demand (BOD) of the seawater in each treatment are given, determined through oxygen consumption using dark incubations over 24 h and referring the estimated changes to the water volume of the incubation (n = 3). Data represent mean ± SD (n = 6) and the results of a one-way ANOVA (p<0.05) performed to determine significant differences in BOD between treatments, are indicated by different letters.