Wildfires continue to threaten California and have recently become more frequent and intense. As a response, federal agencies such as the U.S. Forest Service (USFS) treat the perimeter of wildfires with fire retardant (FR) in attempt to control the fire. Previous studies have focused on the effects of FR on individual species, but few have examined the effects on plant and invertebrate communities within an ecosystem. We investigated the effects of increasing concentrations of FR on invertebrate and plant abundance and biodiversity in California vernal pool mesocosms. Three fire-retardant concentrations (Control, Diluted, Undiluted) were applied in four replicates of each treatment at the California State University, Sacramento Arboretum. Mesocosms were lined with vernal pool soil that contained common vernal pool plant seeds and invertebrate eggs. California vernal pools are imperiled ecosystems that support dozens of threatened and endangered species. Mesocosms were filled from March to May 2022, and sampling of organisms and water quality occurred every two weeks. Water quality measurements included pH, turbidity, conductivity, chlorophyll a, nitrates, and phosphates. Fire retardant was found to have effects on vernal pool water quality, biodiversity, and community composition. Chlorophyll-a, conductivity, and turbidity increased with FR addition. Total species richness decreased and abundance increased with FR addition.