Rapid climate change increases diversity and homogenizes composition of coastal fish at high latitudes

Abstract

Rapid warming at high latitudes triggers poleward shifts of species' distributionsthat impact marine biodiversity. In the open sea, the documented redistributionsof fish lead to a borealization of Arctic fauna. A climate-driven borealization andincreased species diversity at high latitudes are also expected in coastal fish com-munities, but they have not been previously documented on a large, biogeographicscale. Here, we investigate the impact of temperature change over the last 25 yearson fish communities along the coast of Norway. The study area, spanning differentecoclimatic zones between 62° and 71° N, harbors over 200 species of boreal andArctic fish. Several of these fish species are harvested by coastal and indigenouscommunities, influencing settlement geography and livelihood. The long-term dataon coastal water temperatures and fish species were obtained from monitoring sta-tions and scientific surveys. Water temperature measured at three fixed samplingstations distributed along the coast show increased temperatures during the studyperiod. The fish species distribution and abundance data were obtained from theannually standardized scientific bottom trawl survey program. Fish species rich-ness, which was highest in the south, increased with warming first in the south andthen, gradually, further north, eventually affecting biodiversity in the whole studyarea. Fish community composition showed a distinct latitudinal pattern early in thestudy, with Arctic fish species confined to the north and boreal species dominat-ing the south. The poleward shifts eventually eroded this zoogeographic pattern,resulting in more boreal fish species in the north and an increased homogenizationof species composition along the Norwegian coast. The climate-driven reorganiza-tion of fish communities affects coastal ecosystems that are exposed to fisheries,aquaculture, and other rapidly expanding human activities, stressing the urgentneed for a climate adaptation of integrated coastal management.