California is the leading consumer of seafood in the U.S. and relies on the aquaculture industry to provide consistent, high quality farmed shellfish. Aquaculture in California is focused on the non-native Manila littleneck clam (Venerupis philippinarum), a species with established markets and a suitable shelf-life – i.e., time a clam remains edible after leaving the farm. Shelf-life duration is an important factor in determining the commercial viability of a species, and it can be influenced by grow-out conditions, harvest methods, and post-harvest storage or transportation conditions. In the current study, we aim to assess the viability of commercially culturing two of California’s endemic clam species - the Pacific littleneck clam (Leukoma staminea) and the Pismo clam (Tivela stultorum) - on a commercial shellfish farm in Morro Bay, California. Specifically, we are investigating whether the intertidal height at which clams are out-planted on a farm (i.e., low vs. high intertidal) influences shelf-life or environmental stress tolerance in these two species of endemic clams, with a focus on comparison to the commonly cultured non-native Manila littleneck. To this end, we conducted a baseline determination of shelf-life among the three species of clams following adjustment to common garden conditions at the Cal Poly pier. Clams (n=30/species) were held in either 4˚C air emersion (to imitate farmed shellfish transport and storage conditions) or 15˚C seawater submersion (control). Individuals were then monitored daily for survivorship until all endemic clams died, and the LT50 (time to 50% mortality) could be determined for each species. To date, we have found that native Pacific littleneck has an LT50 of 9 days, whereas the non-native Manila littleneck has an LT50 of 23 days. Pismo clam data collection is ongoing. In addition to shelf-life determination assays, we harvested hemolymph tissues from each of the three species of clams (n=18/species) following 72h of emersion stress. We will use these samples to compare baseline immunocompetence between the three species via measurements of total hemocyte counts (THC) and plasma lysozyme activity, bacteriolytic elements central to the innate immune response of invertebrates. Following these baseline assessments, we will outplant clams from each species at two tidal heights (+2 MLLW and +0 MLLW; n=120 clams/species/tidal height) and track growth and survival across a 6 month monitoring period. At the end of this grow-out period, these clams will be used to evaluate whether intertidal position has an effect on shelf-life or environmental stress tolerance (measured as survival during exposure to 4˚C air emersion or to combined heat stress and hypoxia) in any of these species. Understanding the factors that impact shelf-life and environmental stress resilience in emerging native clam species is crucial for informing aquaculture practices, and the data we collect will be directly disseminated to local and regional shellfish farmers through existing relationships.