BackgroundThe California Coastal Prairie has the highest biodiversity of North America's grasslands, but also has the highest percentage of urbanization. The most urbanized part of the California Coastal Prairie is its southernmost area, in Los Angeles County. This southernmost region, known as the Los Angeles Coastal Prairie, was historically dotted with vernal pools, and has a unique biodiverse composition. More than 99.5% of its estimated original 95 km2 (23,475 acres), as well as almost all its vernal pool complexes, have been lost to urbanization.The Madrona Marsh Preserve, in Torrance, California, safeguards approximately 18 hectares (44 acres) of Los Angeles Coastal Prairie and includes a complex of vernal pools. Its aquatic biodiversity had been studied, predominantly to genus level, but its terrestrial macro-invertebrates were virtually unknown, aside from butterfly, dragonfly, and damselfly observations.New informationIn order to better understand the biodiversity at the Madrona Marsh Preserve, a minimally-invasive macro-invertebrate inventory was conducted. The results of this inventory, with 689 invertebrate organisms recorded, covering eight phyla, 13 classes, 39 orders, and 222 families, are presented in this document.