Shifting seas: understanding deep-time human impacts on marine ecosystems.

Humans have interacted with, and impacted, marine ecosystems for millennia. During this time, the oceans have experienced ecosystem degradation through harvesting, habitat change, pollution, the introduction of invasive species and climate change. Despite extensive documentation of substantial recent anthropogenic impacts, our understanding of ancient marine biodiversity remains limited for many ocean regions. This theme issue advances our knowledge of past oceans, revealing how diverse perspectives from across disciplines can provide new insights into marine anthropogenic exploitation over thousands of years. Through engaging a range of source materials, including material remains, historical records and palaeoenvironmental archives, the contributions reveal shifting seas responding to both natural climatic changes and human impacts. Collectively, these outputs demonstrate the value of interdisciplinarity and cross-cultural approaches in understanding ocean change. As marine restoration programmes expand globally, combining disciplinary approaches and novel methods across deep time can provide novel baseline data against which to measure recovery and raise ambition for marine conservation. Beyond biodiversity baselines, understanding past ocean changes can provide key insights into the mechanisms through which human impacts alter marine ecosystems, allowing us to learn from our ancestors' effective and ineffective ocean stewardship practices. Just as diverse ecosystems are buffered against change, diverse human-ocean interactions are important for flourishing future seas.This article is part of the theme issue 'Shifting seas: understanding deep-time human impacts on marine ecosystems'.