The present study determined whether increased mortality and delayed development of larval crabs fed heterotrophic prey that themselves have been fed toxin-containing algae is due to toxicity effects or nutritional deficiency. The effects on larval crabs of previous exposure to heterotrophic prey fed toxin-containing algae were examined. Effects of varying length of exposure of larvae to toxin-containing prey were also examined. The rotifer Brachionus plicatilis was used as a heterotrophic prey source for three larval crab species (Lophopanopeus bellus, Metacarcinus magister, and Glebocarcinus oregonensis). Two rotifer treatments were created, one of rotifers fed a toxin-containing alga (Alexandrium andersoni or A. fundyense); the other of rotifers fed a non-toxic, nutritionally sufficient alga (Isochrysis galbana). To distinguish between toxic and nutritional effects, groups of larvae were fed various combinations of the two rotifer types. Diet treatments included the following ratios of toxin-containing algal fed and non-toxic algal fed rotifers: 100%/0%, 75%/25%, 50%/50%, 25%/75%, and 0%/100%. Larval crabs showed no differences in feeding rates or feeding preferences for the two rotifer diets. Crab survival was lower on the 100% toxin-containing algal fed rotifer diet when compared to the 100% nontoxin- containing algae fed rotifer diet for all three crab species. In all three crab species, stage duration was also extended in larvae fed the 100% toxin-containing algal fed rotifers compared to the 100% non-toxin-containing algal fed rotifers. Increased survival and accelerated development when toxin-containing rotifers were replaced in treatments with non-toxin-containing rotifers implicates nutritional deficiency in the former diet rather than its potential toxic effects. Reduction in time of exposure to a prey source reduced survival and extended development to a greater degree in toxin-containing rotifer treatments than in non-toxincontaining diets. There was no apparent effect of prior exposure to toxin-containing prey on survival or stage duration of later larval stage exposed to the same diet. Larval crabs face an unpredictable and complex prey environment once they enter the plankton. Encounters with Harmful Algal Blooms (HAB) or heterotrophic prey that have ingested HAB species may injure larvae that have no other food source. While my research suggests that nutritional deficiency of the rotifers fed toxin-containing algae causes higher mortality rates and delayed development in the crab larvae, toxin transfer cannot be totally eliminated and a combination of the two factors is most likely causing the negative effects. If the prey environment for these larval crabs includes a nutritionally sufficient animal prey source, negative impacts (i.e. delay in stage duration and decreased survival) caused by exposure to HABs and prey that have ingested HABs can be supplemented.