The onset of the Anthropocene has coincided with enormous global declines in natural ecosystems, leading to losses in the valuable goods and ecosystem services they provide. This global decline, in conjunction with growing recognition of the ecological importance of natural ecosystems, has generated a pressing need for restoration. Effective ecosystem restoration relies on accurate identification of the cause of decline and clear metrics of success, which are only possible with baseline data of both the pre‐degradation and pre‐restoration ecosystems. However, the establishment of these baselines can be difficult as different potential information sources each have benefits and drawbacks. Determining an efficient method to balance these diverse information sources and generate robust baselines is vital to achieving the United Nations' goal of massively scaled‐up ecosystem restoration. Here we expand on the concept of multidisciplinary baselines, or the combined use of sources and methods across a wide disciplinary spectrum to establish comprehensive and reliable ecosystem baselines, and use mussel reefs in the South Island of New Zealand as a test case. Using a combination of comprehensive historical review, extensive shoreline surveys, and local ecological knowledge, we demonstrate that local mussel abundances decreased by 97% since the mid‐1960s as a result of overharvesting, leaving the extant populations scattered, small, and without recovery. This study demonstrates that harnessing multidisciplinary baselines allows for the consolidation of qualitative and quantitative estimates of ecosystem change over hundreds of years, as well as confirmation of causes of ecosystem degradation, and clear documentation of current ecosystem state beyond what is possible from any individual source. This approach to establishing ecosystem baselines also provides valuable avenues for the advancement of restoration by quantifying the temporal and geographic scales of ecosystem decline, identifying areas for intervention, and establishing clear metrics of success.

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 academiaaffiliated 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.

The global loss of marine ecosystem engineers has caused an unprecedented decline in biodiversity. Although wild shellfish habitats have been shown to support biodiverse ecosystems, little is known about how biodiversity is altered by restored shellfish habitats, particularly mussels. To explore the biodiversity response to restored mussel habitats we deposited mussels on the seafloor in 1.5 × 1.5 m plots across a gradient of benthic environments. To understand a holistic community response, this study looks at the response of three faunal classifications over 1 year: infauna, epifauna, and pelagic fauna, compared with adjacent control plots (no mussels). The restored mussel habitats recorded 42 times more demersal fish than control areas, while macroalgae and mobile benthic invertebrates had over a twofold increase in abundance. Overall, the addition of mussels to the seafloor resulted in a general reduction of infaunal abundance and biodiversity, but an increase in epifaunal and pelagic faunal abundances, specifically from those species that benefit from benthic habitat complexity and an increase in food availability. From a management perspective, we highlight location-specific differences to consider for future restoration efforts, including environmental conditions and potential observed factors such as nearby sources of species, particularly predators, and relevant demersal fish ranges. Ultimately, measuring biodiversity responses in small-scale studies will serve as a valuable guide for larger scale restoration efforts and this study recommends considerations to enhance biodiversity outcomes in restored mussel habitats.