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Globally, shellfish reefs have experienced unprecedented declines from historical levels, imperiling the surrounding ecosystems and the services they provide. Shellfish conservation and restoration projects have emerged to combat and reverse this decline but are hindered by a scattered knowledge base and a lack of evidence‐based best practice. To address this concern, we conducted a systematic review of English‐language peer‐reviewed articles studying the impacts of conservation‐based actions on reef‐building bivalves. A comprehensive search identified 281 relevant articles for the review. Articles were then categorized to establish the temporal and geographic extent of shellfish reef conservation research, quantify collaboration within the field, and develop a systematic map of the distribution of evidence across intervention and outcome categories. The results confirm a substantial increase in shellfish reef research with 72% of articles published since 2010. However, this evidence base is uneven, with 80% of research occurring in the United States and Northern Europe, 71% on only oysters, and 58% by only academia‐affiliated authors. The systematic map of linkages and gaps also reveals disparities in the evidence base, as ecological interventions and outcomes are undertaken and measured at a far greater rate than social interventions and outcomes, despite evidence that social aspects are critical components of conservation work. To ensure future conservation practitioners have evidence that is relevant to the circumstances of their projects, this evidence base needs to be diversified and we offer recommendations on reprioritizations for future research as well as a comprehensive database of existing shellfish conservation papers. [ABSTRACT FROM AUTHOR]

Native oyster reefs once dominated many estuaries, ecologically and economically. Centuries of resource extraction exacerbated by coastal degradation have pushed oyster reefs to the brink of functional extinction worldwide. We examined the condition of oyster reefs across 144 bays and 44 ecoregions; our comparisons of past with present abundances indicate that more than 90% of them have been lost in bays (70%) and ecoregions (63%). In many bays, more than 99% of oyster reefs have been lost and are functionally extinct. Overall, we estimate that 85% of oyster reefs have been lost globally. Most of the world's remaining wild capture of native oysters (> 75%) comes from just five ecoregions in North America, yet the condition of reefs in these ecoregions is poor at best, except in the Gulf of Mexico. We identify many cost-effective solutions for conservation, restoration, and the management of fisheries and nonnative species that could reverse these oyster losses and restore reef ecosystem services. [ABSTRACT FROM AUTHOR]