Effects of changing pCO2 and phosphate availability on domoic acid production and physiology of the marine harmful bloom diatom Pseudo‐nitzschia multiseries

Abstract

Some members of the diatom genus Pseudo‐nitzschia produce the toxin domoic acid (DA), which through trophic transfer causes mass mortalities of wildlife, shellfish harvesting closures, and risks to human health. Nutrient and micronutrient limitation have been shown to regulate DA production. This study tested the hypothesis that changing partial pressure of CO2 (pCO2) can interact with nutrient limitation to help determine cellular DA levels, an environmentally relevant issue in light of current increases in atmospheric pCO2. Cultures of the toxic species Pseudo‐nitzschia multiseries were incubated using semicontinuous methods under a matrix of three pCO2 conditions: ∼ 22 Pa (220 ppm), ∼ 41 Pa (400 ppm), and ~ 74 Pa (730 ppm), and two phosphate concentrations: 20 μmol L−1, P‐replete; and 0.5 μmol L−1, P‐limited. DA production was regulated by both pCO2 and phosphate availability. DA concentrations were 30–50 times higher in P‐limited cultures compared to P‐replete ones, at the same pCO2 levels. Increasing CO2 levels stimulated DA production under both nutrient conditions, but especially in P‐limited cultures, where DA levels increased approximately four times over the pCO2 range examined. Growth rates, primary productivity, photosynthesis vs. irradiance parameters, and cellular elemental ratios also responded interactively to the availability of both CO2 and phosphate. Our results raise the possibility that growth rates and toxicity of the diatom Pseudo‐nitzschia multiseries could increase substantially in the future high‐CO2 ocean, suggesting a potentially escalating negative effect of this harmful algal bloom species on the future marine environment.