Toxic red tide algae are a widespread and growing threat to aquatic ecosystems, fishing economies, and human health. One particular red tide algal species, Karenia brevis, produces neurotoxic chemicals called brevetoxins, which can cause massive fish kills along with the poisoning of humans who ingest brevetoxin-contaminated seafood. We conducted several experiments to assess the effects of exposure to K. brevis on the survival, growth, and development of Crepidula fornicata, a species of marine snail that is common in the Gulf of Mexico, where K. brevis regularly blooms, and whose larvae, juvenile, and adult life stages are a potential prey source for many commercial species that reside there. In addition to its overlapping range with K. brevis, C. fornicata has become a prolific invasive species in many parts of the world and is being considered as a potential aquaculture species in its own right. We exposed C. fornicata larvae to medium and high bloom concentrations of K. brevis and looked at the impact on larval survival, shell length, shell weight, tissue weight, feeding rates, and metamorphosis. While there were no significant effects of K. brevis exposure on the short-term survival of C. fornicata larvae, there were several concentration dependent sub-lethal effects, including slower larval growth rates, elevated feeding rates, and lower response to cues for metamorphosis. Slower growth and reduced metamorphosis both extend the amount of time spent in the larval veliger stage, which could increase the vulnerability of C. fornicata larvae to predators and has implications for the dispersal and settlement of the species. Exposure to brevetoxins during the larval stage also has the potential to impact post-metamorphic survival and growth.