Ancient clam gardens magnify bivalve production by moderating temperature and enhancing sediment carbonate

Humans have been developing management systems to support resilient food production through social-ecological feedbacks for millennia. On the Northwest Coast of North America, Indigenous peoples have sustained a diversity of fisheries through management innovations including designated access rights, harvest restrictions, and enhancement strategies. To elucidate how clam gardens, intertidal rock-walled terraces constructed by people in the Late Holocene, increased bivalve production, we quantified environmental variables and transplanted clams (Leukoma staminea) in present-day clam gardens and non-walled control beaches on the coast of western Canada. We found that higher bivalve biomass and densities in clam gardens could be attributed to the effect of terracing on ambient temperature and elevated sediment carbonate associated with crushed shell. These same variables drove detectable differences in transplanted clam growth rates. This study illuminates ecological mechanisms underlying this ancient innovation that could be used to enhance food security and confer resilience to impending oceanic changes.