Systematic review of global historical marine ecology reveals geographical and taxonomic research gaps and biases.

The field of historical marine ecology (HME) developed two decades ago to address a lack of knowledge about long-term declines in the ocean. Here, we conduct, to our knowledge, the first global systematic review of HME, analysing 543 peer-reviewed articles to ask: what has been learnt and what gaps remain? The diversity of sources used in HME-from Roman texts to twentieth-century catch records-illustrates the methodological richness of the field. Most articles used documentary sources (68%) and produced quantitative outputs (54%), reflective of HME's origins in marine science. Research focused on economically and culturally valuable taxa like fishes, which account for 41% of articles. Most research found decline (85%), while articles finding increase relied on significantly more recent data, underscoring the need for long-term data to assess decline. Strikingly, we identify geographical gaps and biases that suggest a need for targeted initiatives to support HME in the Global South. For instance, nearly as much research focused on the California Current as the entire Indian Ocean, and 74% of first authors worked in North America and Europe. Understanding the colonial legacy of marine resource extraction and the history of artefact theft that disadvantages Global South researchers should guide the future of HME.This article is part of the theme issue 'Shifting seas: understanding deep-time human impacts on marine ecosystems'.