A growing body of evidence shows that microplastic ingestion causes harmful effects in many marine organisms including bivalves, but little is understood on the effects of early life stage exposure, when most vulnerable to environmental stress. The Eastern Oyster (Crassostrea virginica) is a valuable ecological and economic resource along the east coast of the United States, making it important to understand the dynamics between microplastics and oysters. This study investigates the physiological response of C. virginica larvae during exposure to microfibers. Two polymers, commonly found in the coastal environment, were chosen for the microplastic exposure solutions: polyethylene terephthalate (PET, polyester) (50/50 mix of 14x14 and 14x28 μm) and nylon 6,6 (50/50 mix 10x10 and 10x30 µm). Larvae (6-7 days-post-fertilization) were exposed to one type of polymer solution at 100 or 1000 microfibers mL-1 for 6 days. Physiological rates (respiration, algal clearance, carbon assimilation, and growth) were measured. Preliminary results showed that C. virginica larvae responded differently to PET and nylon even though the fibers were similar in size. PET caused a significant growth penalty at 1000 microfiber mL-1 after 6 days but nylon fibers caused a significant increase in growth for the same concentration. Both polymer fibers altered algal clearance rates and respiration rates. Further results of the other parameters measured will be presented and discussed. This work details the ingestion of microplastics during the larval stage and highlights the critical need to investigate impacts of microplastics at all life stages.