Blue carbon ecosystems-seagrasses, tidal marshes , and mangroves-serve as dense carbon sinks important for reducing atmospheric greenhouse gas concentrations, yet only recently have stock estimates emerged. We sampled 96 blue carbon ecosystems across the Victorian coastline (southeast Australia) to quantify total sediment stocks, variability across spatial scales, and estimate emissions associated with historical ecosystem loss. Mean sediment organic carbon (C org) stock (±SE) to a depth of 30 cm was not significantly different between tidal marshes (87.1 ± 4.90 Mg C org ha-1) and mangroves (65.6 ± 4.17 Mg C org ha-1), but was significantly lower in seagrasses (24.3 ± 1.82 Mg C org ha-1). Location (defined as an individual meadow , marsh, or forest) had a stronger relationship with C org stock than catchment region, suggesting local-scale conditions drive variability of stocks more than regional-scale processes. We estimate over 2.90 million ± 199,000 Mg C org in the top 30 cm of blue carbon sediments in Victoria (53% in tidal marshes, 36% in seagrasses, and 11% in mangroves) and sequestration rates of 22,700 ± 5510 Mg C org year-1 (valued at over $AUD1 million ± 245,000 year-1 based on the average price of $AUD12.14 Mg CO 2 eq-1 at Australian Emissions Reduction Fund auctions). We estimate ecosystem loss since European settlement may equate to emissions as high as 4.83 million ± 358,000 Mg CO 2 equivalents (assuming 90% remineralization of stocks), 98% of which was associated with tidal marsh loss, and what would have been sequestering 9360 ± 2500 Mg C org year-1. This study is among the first to present a comprehensive comparison of sediment stocks across and within coastal blue carbon ecosystems. We estimate substantial and valuable carbon stocks associated with these ecosystems that have suffered considerable losses in the past and need protection into the future to maintain their role as carbon sinks.