Wild Olympia oysters have not recruited in the Elkhorn Slough since 2012 and the risk of local extinction is looming. Mortality in the surviving adults from this last recruitment continues to decrease their population density, reducing opportunities for successful reproduction. Habitat degradation from a century of land-use changes additionally decreases available substrate and their potential population size. In response, The Elkhorn Slough National Estuarine Reserve partnered with Moss Landing Marine Laboratories (MLML) and California Sea Grant to breed oysters from the remaining population sites in the hatchery and repopulate the estuary.
This report describes our conservation aquaculture effort to support native oyster recovery by outplanting hatchery-raised juveniles into the wild population. In addition to monitoring growth and survival, we conducted focused experiments in the lab to examine different responses to varying food and temperature conditions between each stage. This information complements our aim to reestablish a self-sustaining Olympia oyster population by both improving hatchery methods and identifying optimal outplant locations. We will highlight our experiments that characterize the physiological effects on food availability on assimilation efficiency in adult and juvenile Olympia oysters.
Adult oysters were collected from the Elkhorn Slough, CA in June 2021 and spawned at the MLML hatchery facility. Oysters in both life-stages were fed a mixed live microalgae diet cultured on site. Consumption and subsequent excretion were evaluated from three food availability treatment levels between 1 and 6 x 105 cells mL-1. Filtration feeding was measured as clearance rate. The excreted feces and pseudofeces were then collected and the total organic and energy content excreted was determined using ash-free dry weights. Assimilation efficiency was calculated from the percentage of food energy absorbed in digestion. Results will be integrated with metabolic data measured as respiration from oxygen consumption in closed chambers. These values together form the baseline for separate energy budgets between life stages.
By studying changes to the energy pathway with age or with environmental conditions, this study aims to identify differences in the amount of energy being allocated for growth and reproduction. Changes in the energy balance indicate potential population bottlenecks during early life stages. In addition, understanding differences in the oysters’ energy budget will optimize hatchery processes and grow-out procedures to support aquaculture efficiency.