Climate warming drives large-scale changes in ecosystem function.

The Barents Sea is the continental shelf sea to the north of Scandinavia and Northwest Russia, and it supports some of the richest fisheries in Europe. Until recently, the northern Barents Sea was dominated by small-sized, slow-growing fish species with specialized diets, mostly living in close association with the sea floor. Concomitant with rising sea temperatures and retreating sea ice, these fishes are being replaced by fast-growing, large-bodied generalists moving in from the south. In PNAS, Frainer et al. (1) document these changes and investigate consequences for ecosystem functioning, a topic of interest far beyond the Barents Sea. Global climate change leads to a poleward displacement of species, with the fastest responses occurring in the oceans, where there are fewer physical barriers to movement than on land (2). All species do not move at the same pace, however; hence, new species configurations emerge. These alterations in biogeographic patterns have unknown consequences for ecosystem functioning and services. The emerging scientific field of functional biogeography addresses this knowledge gap by integrating biogeographic information on species distributions with information on how species affect ecosystem functioning (3). Functional biogeography focuses on the traits that describe the ecological roles of organisms, such as feeding type and body size of animals. Focusing on functional traits instead of species can provide new insights into how climate and other factors affect ecosystem functioning. For example, using functional biogeography to study forests on a global scale, Reich et al. (4) demonstrated that the proportion of plant biomass in foliage relative to roots was higher in warm compared with cold climate zones, with implications for how climate change may impact carbon storage in forest ecosystems. However, few studies before that of Frainer et al. (1) have used functional biogeography to investigate how climate change affects ecosystem functioning at large geographic scales in marine environments. Moreover, the study of Frainer et al. (1) is the first to do so in the Arctic. This research is particularly timely as some of the world’s highest temperature increases in recent decades have occurred in the Arctic (5), and the region can be seen as an early indicator of global change. Based on abundance data from a bottom trawl survey conducted in the Barents Sea between 2004 and 2012, Frainer et al. (1) identify 52 fish species that could be described using 15 functional traits, including body size, longevity, fecundity, growth rate, habitat, diet characteristics, and position in the food web. The authors first asked what the distribution of traits among species can tell us about the Barents Sea fish community. They found that themajority of the species displayed traits typical of Arctic bottom fishes (“Arcticlike traits”): small body size, low growth rate, and specialist diet mostly consisting of other organisms on the Fig. 1. Climate change leads to large-scale changes in ecosystem functioning, as represented by functional trait distributions in bottom fish communities in the Barents Sea (1). The spatial distributions shown are simplified from figure 1 of ref. 1 and are not exact in all details. Fish illustrations are from Wikimedia Commons. Arctic fish illustration: Liparis liparis by Samuel Garman, 1892, published in the United States before 1923 and public domain in the US. Boreal fish illustration: Gadus morhua, in the public domain because it contains materials that originally came from the US National Oceanic and Atmospheric Administration, taken or made as part of an employee’s official duties.