Ascidians are marine non-vertebrate chordates with high levels of genetic polymorphism. This dissertation documents the analysis of their physical abundance and diversity within the Santa Barbara Yacht Harbor as well as an in-depth analysis of the levels of genetic polymorphism of these ascidians species. Of the sampled species, two of them have had their genomes sequences while the remaining eight have little to no sequence information available. The species included in this study are Aplidium californicum, Ascidia ceratodes, Ascidia zara, Botryllus schlosseri, Botrylloides diegensis, Botrylloides violaceus, Ciona intestinalis, Ciona savignyi, Styela clava, and Styela plicata. The most surprising result of this analysis is that the factor most strongly correlated with the level of genetic polymorphism within the invasive species is the time introduction, and it is a negative correlation, those invasive species most recently introduced had the highest level of polymorphism and those invasive species which have been well established have the lowest levels of polymorphism.