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Among <i>Pseudo-nitzschia</i> species, some produce the neurotoxin domoic acid (DA), a source of serious health problems for marine organisms. Filter-feeding organisms—e.g., bivalves feeding on toxigenic <i>Pseudo-nitzschia</i> spp.—are the main vector of DA in humans. However, little is known about the interactions between bivalves and <i>Pseudo-nitzschia</i>. In this study, we examined the interactions between two juvenile bivalve species—oyster (<i>Crassostrea gigas</i>) and scallop (<i>Pecten maximus</i>)—and two toxic <i>Pseudo-nitzschia</i> species—<i>P. australis</i> and <i>P. fraudulenta.</i> We characterized the influence of (1) diet composition and the <i>Pseudo-nitzschia</i> DA content on the feeding rates of oysters and scallops, and (2) the presence of bivalves on <i>Pseudo-nitzschia</i> toxin production. Both bivalve species fed on <i>P. australis</i> and <i>P. fraudulenta</i>. However, they preferentially filtered the non-toxic <i>Isochrysis galbana</i> compared to <i>Pseudo-nitzschia</i>. The presence of the most toxic <i>P. australis</i> species resulted in a decreased clearance rate in <i>C. gigas</i>. The two bivalve species accumulated DA in their tissues (up to 0.35 × 10⁻³ and 5.1 × 10⁻³ µg g⁻¹ for <i>C. gigas</i> and <i>P. maximus</i>, respectively). Most importantly, the presence of bivalves induced an increase in the cellular DA contents of both <i>Pseudo-nitzschia</i> species (up to 58-fold in <i>P. fraudulenta</i> in the presence of <i>C. gigas</i>). This is the first evidence of DA production by <i>Pseudo-nitzschia</i> species stimulated in the presence of filter-feeding bivalves. The results of this study highlight complex interactions that can influence toxin production by <i>Pseudo-nitzschia</i> and accumulation in bivalves. These results will help to better understand the biotic factors that drive DA production by <i>Pseudo-nitzschia</i> and bivalve contamination during <i>Pseudo-nitzschia</i> blooms.