Toxic blooms of the diatom genus Pseudo-nitzschia are common in the coastal waters of eastern boundary upwelling systems (EBUS), including those of the California Current System (CCS) off the west coast of the United States, where ocean acidification (OA) is unequivocally observed. However, the relationship between toxic blooms with their elevated domoic acid (DA) concentrations and regions of decreased pH levels is still uncertain and variable. Our laboratory study used unialgal cultures of acclimated P. multiseries – a toxigenic species isolated from Monterey Bay, a well-known DA hotspot, to examine this relationship and determine whether ocean acidification promotes more rapid cellular growth and/or increased DA production in response to declining pH under both macronutrient-sufficient and -deficient conditions expected in episodic upwelling regions such as the CCS which exhibits silicate limitation of diatom growth in some areas. Unlike earlier studies with other strains and species of Pseudo-nitzschia, OA does not affect the specific growth rate achieved by P. multiseries. Although cellular DA levels greatly increase with silicate deficiency, there is no significant relationship with pH, and rates of DA production do not increase at reduced pH levels of 7.94 and 7.82 relative to 8.08 (control). Our results demonstrate the importance of using ecologically-relevant species and suggest that the impacts of OA differ greatly among toxigenic species and their degree of macronutrient sufficiency.
Cochlan et al. (Fri,) studied this question.
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