European continental shelf seas have experienced intense warming over the last 30 33 years 1 . In the North Sea, fishes have been comprehensively monitored throughout 34 this period and resulting data provide a unique record of changes in distribution and 35 abundance in response to climate change 2,3 . We use these data to demonstrate the 36 remarkable power of Generalised Additive Models (GAMs), trained on data earlier in 37 the time-series, to reliably predict trends in distribution and abundance in later years. 38Then, challenging process-based models that predict substantial and ongoing 39 poleward shifts of cold-water species 4,5 , we find that GAMs coupled with climate 40 projections predict future distributions of demersal (bottom-dwelling) fish species 41 over the next 50 years will be strongly constrained by availability of habitat of suitable 42depth. This will lead to pronounced changes in community structure, species 43 interactions and commercial fisheries, unless individual acclimation or population-44 level evolutionary adaptations enable fish to tolerate warmer conditions or move to 45 previously uninhabitable locations. 46 47While the temperature of the world's oceans has gradually risen through the 20 th Century, 48 the northeast Atlantic has experienced particularly intense warming, resulting in the North 49 Sea mean annual sea-surface temperature increasing by 1.3°C over the last 30 years 1 , a 50 rate four times faster than the global average 6 . Predictions for the North Sea suggest a 51 further 1.8°C rise in sea-surface temperatures during the next five decades (Hadley Centre 52 QUMP_ens_00 model, unpublished data supplied by J. Tinker) (Fig. 1). Impacts of recent 53 warming on northeast Atlantic marine ecosystems have been diverse, including 54 reorganisation of the plankton community 7 , modification to the phenology of fish spawning 8,9 , 55 and alterations of ecosystem interactions 10,11 . Due to its longstanding economic importance 56 to fisheries (reported landings in 2007 valued at $1.2 billion 1 ) and other industries, the 57 ecology of the North Sea has been intensively monitored throughout this period of recent 58 warming. 59 60 3 Analyses of North Sea fish surveys have revealed northerly range expansions of warmer-61 water species 12 , population redistributions to higher latitudes 2 and deeper water 13 , and 62 widespread changes in local abundance associated with warming, with impacts on 63 community structure 3 . This substantial modification to fish community composition in the 64 region has had an observable economic impact on fisheries, with landings of cold-adapted 65 species halved but landings of warm-adapted species increasing 2.5 times since the 1980s 3 ; 66 a pattern also identified in other marine ecosystems 14 . With a uniquely rich fish abundance 67 time-series from the period of warming, it is possible to split these data to assess how 68 predictions made using data from earlier years match observations from later years; a 69 validation approach which has been...

Highlights d Global-scale analysis of marine species shows abundance changes linked to warming d Increases at poleward sides of species ranges reflect new ecological opportunities d Declines at equatorward sides show failure to adapt to rapid climate change d Results imply future warming will impact further on abundance of marine species