Ancient clam gardens increased production: Adaptive strategies from the past can inform food security today

Maintaining food production while sustaining productive ecosystems is among the central challenges of our time, yet it has been for millennia. We quantified the productivity of ancient clam gardens, intertidal rock-walled terraces made by humans, by comparing the biomass and density of surveyed bivalves and growth rates of transplanted Leukoma staminea (littleneck clams) at replicate clam garden and non-walled beaches in British Columbia, Canada. We found that clam gardens had significantly shallower slopes, significantly greater densities of L. staminea and Saxidomus giganteus, and higher growth of transplanted L. staminea. As predicted, productivity varied as a function of tidal height, beach position and size class. Consequently, we provide strong empirical and experimental evidence that ancient clam gardens likely increased clam productivity by altering beach slope, expanding optimal intertidal habitat thereby enhancing growing conditions for clams. These results reveal how a traditional form of mariculture can inform resilient food security strategies today.