The effects of ocean acidification on growth, photosynthesis, and domoic acid production by the toxigenic diatom Pseudo-nitzschia australis

A northern California strain of Pseudo-nitzschia australis was examined using nonaxenic, batch cultures to examine the effects of more acidic conditions (reduced pH due to increased pCO2) on the growth, photosynthesis, and domoic acid production of this toxigenic diatom. Specific growth rates at the lowest pH tested (7.8) were 30 percent lower than the other three pH treatments (8.1, 8.0, 7.9). Macronutrient drawdown ratios of Si:N and Si:P decreased linearly with declining pH. Maximum rates of photosynthesis per cell were significantly elevated in the two lowest pH treatments relative to the control pH of 8.1. Domoic acid (DA) was detected in all pH treatments during both the nutrient-replete exponential growth phase and the nutrient-deplete stationary growth phase. Total cellular DA did not significantly differ among pH treatments during exponential growth, but increased with decreasing pH and reached a maximum of 3.61 pg DA • cell"1 during the stationary phase of growth.