Research PaperEffect of CO2 on growth and toxicity of Alexandrium tamarense from the East China Sea, a major producer of paralytic shellfish toxins

- Strain of Alexandrium tamarense isolated from East China Seas, showed a significant response to elevated CO2 levels in growth and toxicity.
- Strain ATDH grew faster and showed a larger density when exposed to elevated CO2 concentration, especially in the exponential period.
- The concentration per cell of each PST derivate varied and eventually caused the cellular toxicity increased when exposed to higher pCO2.

In recent decades, the frequency and intensity of harmful algal blooms (HABs), as well as a profusion of toxic phytoplankton species, have significantly increased in coastal regions of China. Researchers attribute this to environmental changes such as rising atmospheric CO2 levels. Such addition of carbon into the ocean ecosystem can lead to increased growth, enhanced metabolism, and altered toxicity of toxic phytoplankton communities resulting in serious human health concerns. In this study, the effects of elevated partial pressure of CO2 (pCO2) on the growth and toxicity of a strain of Alexandrium tamarense (ATDH) widespread in the East and South China Seas were investigated. Results of these studies showed a higher specific growth rate (0.31 ± 0.05 day−1) when exposed to 1000 μatm CO2, (experimental), with a corresponding density of (2.02 ± 0.19) × 107 cells L−1, that was significantly larger than cells under 395 μatm CO2(control). These data also revealed that elevated pCO2 primarily affected the photosynthetic properties of cells in the exponential growth phase. Interestingly, measurement of the total toxin content per cell was reduced by half under elevated CO2 conditions. The following individual toxins were measured in this study: C1, C2, GTX1, GTX2, GTX3, GTX4, GTX5, STX, dcGTX2, dcGTX3, and dcSTX. Cells grown in 1000 μatm CO2 showed an overall decrease in the cellular concentrations of C1, C2, GTX2, GTX3, GTX5, STX, dcGTX2, dcGTX3, and dcSTX, but an increase in GTX1 and GTX4. Total cellular toxicity per cell was measured revealing an increase of nearly 60% toxicity in the presence of elevated CO2 compared to controls. This unusual result was attributed to a significant increase in the cellular concentrations of the more toxic derivatives, GTX1 and GTX4.Taken together; these findings indicate that the A. tamarense strain ATDH isolated from the East China Sea significantly increased in growth and cellular toxicity under elevated pCO2 levels. These data may provide vital information regarding future HABs and the corresponding harmful effects as a result of increasing atmospheric CO2.