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Over the last 4 decades there have been major advances in our understanding of the biology, ecology and physiology of seagrasses and their environmental interactions. Despite these advances, there has been relatively little advancement in our understanding of seagrass belowground dynamics. Minirhizotron tubes are a terrestrial ecology method used to visualize root birth, growth and death to evaluate root deployment, development and demography. Our objectives were to adapt the use of minirhizotrons in an intertidal seagrass bed, and to quantify root standing crop, production, mortality and life span of Zostera marina roots in a northwest US estuary. A total of 204 individual roots were observed and tracked over 18 monthly sampling periods. Roots exhibited marked vertical distribution in the sediment with peak root numbers at 9 and 25 cm depth. The median life span for roots deeper than 10 cm in the sediment was 75 d and only 48 d for roots in the top 10 cm of sediment. Root biomass turnover was estimated to be 56.9 g m(-2) yr(-1), while root carbon mass turnover estimate was 16.6 g C m(-2) yr(-1). Although significant logistical obstacles remain (e.g. minirhizotron use in subtidal beds), development of a non-destructive sampling technique for seagrass belowground root dynamics will provide better insight into seagrass root-sediment inter actions that cannot be captured using traditional destructive sampling methods.