Impacts of climate change on marine ecosystem production in societies dependent on fisheries

Growing human populations and changing dietary preferences are increasing global demands for fish1, adding pressure to concerns over fisheries sustainability2. Here we develop and link models of physical, biological and human responses to climate change in 67 marine national exclusive economic zones, which yield approximately 60% of global fish catches, to project climate change yield impacts in countries with di erentdependenciesonmarinefisheries3. Predictedchanges in fish production indicate increased productivity at high latitudes and decreased productivity at low/mid latitudes, with considerable regional variations. With few exceptions, increases and decreases in fish production potential by 2050 are estimated to be<10% (mean+3.4%) from present yields. Among the nations showing a high dependency on fisheries3, climate change is predicted to increase productive potential in West Africa and decrease it in South and Southeast Asia. Despite projected human population increases and assuming that per capita fish consumption rates will be maintained1, ongoing technological development in theaquaculture industry suggests that projected global fish demands in 2050 could be met, thus challenging existing predictions of inevitable shortfalls in fish supply by the mid-twenty-first century4. This conclusion, however, is contingent on successful implementation of strategies for sustainable harvesting and e ective distribution of wild fish products from nations and regions with a surplus to those with a deficit. Changes in management e ectiveness2 and trade practices5 will remain the main influence on realized gains or losses in global fish production. Marine fisheries provide 80Mt of protein and micronutrientrich food for human consumption per year and contribute US$230 billion to the global economy, offering livelihood support to 8% of the world’s population5. With demand for fish products predicted to increase, efforts to support food and livelihood security need to be informed by predictions of changes in fish production and their societal and economic consequences. Biological predictions based on ocean–atmosphere general circulation models (OA-GCMs) have demonstrated that climate change will modify the physical and chemical properties of the oceans, affecting the productivity, distribution, seasonality and efficiency of food webs, from primary producers6 to fish7,8. However, using GCMs to predict fish production has several uncertainties, in addition to their structural and natural variability uncertainties9. First, the resolution of GCMs is too coarse (typically 1–2) to capture the processes that dominate the dynamics of the world’s coastal and shelf regions, such as coastal upwelling and tidal mixing10, which exhibit significantly different responses to climate than the open ocean. Directly addressing the effects of these processes is an important challenge because coastal and shelf regions contribute a quarter of the global primary production and most global fish production11. Second, predicting the impacts of climate change on the ecosystem and fish production remains a challenge, as it depends on the transfer of energy through complex and often compensatory food chain processes12. Approaches at present either make strong habitat or energy transfer assumptions8,13, or focus on predicting impacts on individual species14. Herewe directly address these challenges by developing and applying a highly resolved coupled physical–biological shelf-seas model to 67 marine national exclusive economic zones (EEZs). The model was forced using a single GCM (Institute Pierre Simon Laplace Global Climate Model; IPSL-CM4) under the Intergovernmental Panel on Climate Change (IPCC) SRES (Special Report on Emissions Scenarios) A1B scenario, providing ten-year mean outputs for the present day and 2050. These were used to drive a dynamic size-based food web model to estimate the ecological consequences of climate change on fish production capacity. Finally, we evaluate the societal relevance of these results by looking at the dependency of individual countries on their fisheries sectors in terms of food and livelihood security, as well as at the expected global demand for fish products for an increasing human population. Our results show that in all the shelf regions considered themixed layer depth temperature (MLDT, the depth to which the density difference from the surface is less than 0.03 kg m) is expected to increase when referenced to the present day. By 2050, predicted warming of the mixed layer of shelf seas will range from a moderate 0.2 C in the Irish EEZ to 2.9 C off Korea and East China (Figs 1a and 2a). Our models predict average increases in net primary production of shelf seas of about 14%, slightly larger but still consistent with existing estimates of global primary production change based on coarse-scale GCMs (ref. 6). Ecosystems in higher (lower) latitudes will generally experience production increases (decreases; Figs 1b