Marine microplastics (<5mm) have been commonly found in nearshore environments, including along the California coast. These microplastics may have formed from the weathering and breakdown of larger plastics or may have been manufactured as microplastics (e.g. synthetic fibers, microbeads, and industrial scrubbers). These microplastics are bioavailable to marine species, specifically zooplankton, and can biomagnify through trophic levels to cause chemical and physical harm to zooplankton species. A Schindler-Patalas plankton trap was used to capture zooplankton across fifteen different pier and harbor locations in Southern California. A compound microscope and visual quantification was used to identify zooplankton and microplastic species and sizes within the samples. Twelve different species of zooplankton were identified alongside microplastics that would be bioavailable to them within their habitat at each location. The size distribution of zooplankton was statistically significantly different between pier and harbor sites (D = 0.16, p = 0.012), with pier sites having a higher frequency of plankton in the smaller 0.2 - 0.4mm size range. The size distribution of microplastics did not differ significantly between pier and harbor locations (D = 0.088, p = 0.11). There were predominantly more abundant smaller microplastics (0.0 mm - 0.3 mm) at both piers and harbors, which overlaps the size distribution of small zooplankton present (0.1 mm – 0.5 mm). Due to the feeding mechanisms employed by zooplankton, trophic impacts due to the bioavailability of small microplastic particles are likely. These findings that indicate the high abundance of very small and bioavailable microplastics are alarming because zooplankton are a foundational species in marine food webs. More research is necessary to understand the impacts of ingestion and trophic transfer of microplastics in zooplankton.