Sexual development and symbionts of native Olympia oysters Ostrea lurida naturally settled on cultch deployed in San Francisco Bay, California

Attempts to restore depleted oyster populations are taking place worldwide. The design of effective restoration programs can benefit significantly from knowledge of basic biological processes such as ontogenetic and seasonal reproductive patterns and the presence of potential agents of disease. In June 2007 we deployed oyster shell cultch in a series of mounds in San Francisco Bay, California, USA. In monthly sampling, sixty of the largest oysters recruited onto the cultch were examined histologically to track the reproductive development of the initial settlers. Symbiont presence was also recorded. Sexual development was already occurring in August 2007, 56 days after cultch deployment, with immature males comprising 18% of the sample. Mature sperm and oocytes were observed in September 2007, 92 days following cultch deployment. Brooded larvae were observed in October-November 2007 and April-June 2008, indicating a relatively long reproductive season and confirming that oysters that settle in late spring can reproduce as females by autumn. These results suggest the capacity for rapid population expansion when suitable habitat is available. The oysters were minimally affected by disease, in contrast to the native oyster (Crassostrea virginica) of the US Atlantic and Gulf coasts.