Sea urchins are frequently collected, grown and maintained in aquaculture for developmental and toxicological studies where they serve as model organisms. They are also raised for their gonads as a food source, called uni. Applied studies have used lab-acclimated sea urchins as subjects to demonstrate how sea urchin populations respond to various stimuli with minimal mention of the gut microbiome. Changes in gut microbiome diversity have been observed in a variety of animal models during maintenance in lab settings. Such lab-induced microbiome changes can cascade to influence their animal host, potentially impacting research outcomes and their consistency as the gut microbiome affects the host organism’s development, susceptibility to pathogens, and ability to metabolize and acquire nutrients. The effects of probiotic supplementation and/or fecal microbiota transplantation (FMT) in sea urchins have not been explored to our knowledge. Due to the relationship between microbial diversity and gut function, dysbiosis may dramatically impact urchin health and, consequently, the quality and consistency of urchins raised for food and applied research. Since urchin microbiomes are sensitive to abiotic and dietary conditions, standardization of husbandry is essential for researchers seeking reproducible experimental results. To test the effect of diet and gut microbiome on performance and toxicological outcomes wild sea urchins (Lytechinus variegatus) were collected at Port St. Joe, Florida. They were placed in a 30 tank recirculating system with there being 10 tanks per treatment with 4 urchins individually maintained per tank. Sea urchins were fed a standard reference diet, a standard reference diet with FMT and the EPA approved diet of lettuce for 10-weeks. At the conclusion of the experiment indicators of sea urchin performance for weight gain, survival, and changes in test diameter, gut, gonad, and lantern weights were measured. Gut microbiome was measured and compared for urchins fed the 3 different diets as well as the microbiome of the wild sea urchins. Toxicological outcomes were measured between the wild and laboratory fed sea urchins. This was done to examine the effect of toxicological outcomes on reproductive potential. Data from these outcomes will be presented.