It is widely established that inbreeding can incur heavy costs in a variety of plants, animals, and algae. To date, ten species of kelp have been tested to ascertain the degree to which selfing reduces recruitment of juvenile sporophytes and of those ten species, seven have reduced recruitment when inbred. In this study, I set out to understand whether there is variability in response to self-fertilization among giant kelp gametophytes grown from multiple sites, what those differences are, and how it affects sporophyte recruitment. I collected reproductive sporophylls from fifteen Macrocystis pyrifera individuals in Point Loma, Leo Carrillo State Beach, Carpinteria, and Cayucos, CA. After inducing release of zoospores, I raised gametophytes in both polycultures and monocultures resulting in levels of self-fertilization of 7% and 100% respectively. I recorded the days it took to see the first sporophyte in each dish and a week later counted the number of sporophytes, female gametophytes, and eggs to standardize the data among replicates. I found that, when comparing the density between selfed and outcrossed recruits, there was a reduced number of recruits in selfed than in outcrossed cultures for 3 sites. There was no significant difference in relative cost of self-fertilization among sites. I also found that recruitment was delayed in selfed cultures, but the severity of the delay varied among sites. Eggs existed in an approximately 1:1 ratio to female gametophytes, with the exception of Carpinteria where eggs existed in an approximately 1:2 ratio to female gametophytes. This study demonstrates that Macrocystis pyrifera responds to self-fertilization differently at different sites, that the costs of self-fertilization do not vary among sites, and that self-fertilization results in slower recruitment than outcrossing in giant kelp
