This study determined the effects of selected algal species that commonly occur along the Southern California coast on purple urchin (Strongylocentrotus purpuratus) fertilization and embryo development. Algal blooms occur in Southern California with irregular intensity and timing and are monitored by the Harmful Algae and Red Tide Regional Monitoring Program, which is part of the Southern California Coastal Ocean Observing System (SCCOOS). The Scripps Institution of Oceanography (SIO), on the University of California, San Diego (UCSD) campus, discharges into an Area of Special Biological Significance (ASBS), as designated by the State Water Resources Control Board. As part of the discharge monitoring program, U.S. Environmental Protection Agency toxicity test methods are conducted on samples collected from the outfalls and receiving water twice a year, once during a storm event and once during dry weather. Five marine phytoplankton species were laboratory cultured for testing, including dinoflagellates (Lingulodinium polyedrum, Prorocentrum micans, and Akashiwo sanguinea) and diatoms (Thalassiosira rotula and Thalassiosira psuedonana). A naturally occurring bloom sample collected off of Scripps Pier of A. sanguinea was also used in this study. The hypothesis for this project was that toxic effects to sea urchin egg fertilization and embryo development will be observed at the highest environmentally relevant algal concentrations. Based on available literature, it is further hypothesized that the diatom T. pseudonana will show less of an effect than the dinoflagellates L. polyedrum and A. sanguinea as T. pseudonana is frequently used as a negative control. It is also anticipated that T. rotula, L. polyedrum, and A. sanguinea will have a greater effect than P. micans because of the lower level of biotoxin concentration created by P. micans. Additionally, it was anticipated that there would be an increase in the biotoxin effect after phytoplankton were in seawater overnight at 4 Celsius (°C). Results indicated that the presence through spiking of both laboratory cultured and naturally occurring populations of A. sanguinea in seawater decreased urchin fertilization potential and normal embryo development. The observed effects significantly increased with manual agitation of the algae. This study provides insight into the effects of naturally occurring algal blooms and the potential influence on mandated toxicity testing of the receiving waters in this ASBS.