Ecological extinction caused by overfishing precedes all other pervasive human disturbance to coastal ecosystems, including pollution, degradation of water quality, and anthropogenic climate change. Historical abundances of large consumer species were fantastically large in comparison with recent observations. Paleoecological, archaeological, and historical data show that time lags of decades to centuries occurred between the onset of overfishing and consequent changes in ecological communities, because unfished species of similar trophic level assumed the ecological roles of overfished species until they too were overfished or died of epidemic diseases related to overcrowding. Retrospective data not only help to clarify underlying causes and rates of ecological change, but they also demonstrate achievable goals for restoration and management of coastal ecosystems that could not even be contemplated based on the limited perspective of recent observations alone.Few modern ecological studies take into account the former natural abundances of large marine vertebrates. There are dozens of places in the Caribbean named after large sea turtles whose adult populations now number in the tens of thousands rather than the tens of millions of a few centuries ago (1, 2).

Estuarine and coastal transformation is as old as civilization yet has dramatically accelerated over the past 150 to 300 years. Reconstructed time lines, causes, and consequences of change in 12 once diverse and productive estuaries and coastal seas worldwide show similar patterns: Human impacts have depleted 990% of formerly important species, destroyed 965% of seagrass and wetland habitat, degraded water quality, and accelerated species invasions. Twentieth-century conservation efforts achieved partial recovery of upper trophic levels but have so far failed to restore former ecosystem structure and function. Our results provide detailed historical baselines and quantitative targets for ecosystem-based management and marine conservation. With recognition of their essential role for human and marine life, estuaries and coastal zones have become the focus of efforts to develop ecosystembased management and large-scale restoration strategies. To be successful, these approaches require historical reference points and assessments of the degree and drivers of degradation in an ecosystem context (8, 9).We reconstructed historical baselines and quantified the magnitude and causes of change in 12 temperate estuarine and coastal ecosystems in Europe, North America, and Australia from the onset of human settlement until today (Table 1). We used paleontologic, archaeological, historical, and ecological records (table S1) to quantify changes in 30 to 80 species per system standardized into 22 guilds and six taxonomic and seven functional groups, as well as seven water-quality parameters and species invasions (10). Species were selected for their economic, structural, or functional significance throughout history. We estimated relative abundance of each species over real time and across seven cultural periods reflecting the stage of cultural and market development rather than calendar dates (tables S2 and S3). Relative abundance was quantified as pristine (100%), abundant (90%), depleted (50%), rare (10%), or extinct (0%) (table S4). Recovery was quantified as partial or substantial when increasing from G10% to 910% and 950%, respectively (10). Our estimates are conservative compared with available absolute abundance records.