Recovery lags are common in marine ecosystems, especially following mass mortality events of key habitat-forming species. We investigated the causes of hysteresis (ecological phenomena that block recovery) in intertidal New Zealand cockle (Austrovenus stutchburyi) populations, which have experienced several heatwave-induced mass-mortality events over the past decade. We hypothesised that the sudden loss of large adults removes facilitation feedbacks, linked to sediment stability, which normally enhances the success of juvenile conspecifics. To test our hypothesis, we excluded adult shellfish from 9m2 plots at 23 sites across four estuaries in established cockle beds spanning a natural adult density gradient. We stained juveniles with calcein, transplanted them to exclusion and ambient plots, and after 7 months measured retention, growth, and condition. We also measured sediment transport (a proxy for sediment stability) with bedload and water column traps. We found that adult cockle density significantly influenced juvenile retention, growth, and condition, as well as sediment stability. Multiple biotic and abiotic variables mediated the direction and strength of these responses. Our study signals the existence of feedbacks between the loss of adult cockles and the success of juveniles that may help explain recovery lags in shellfish populations following mass mortality events.