Boreal “Take-over”

Climate change leads to poleward movements of marine species. The Arctic is more sensitive to these changes due to the twice as fast increasing in air temperatures compared to the global average and consequent sea-ice retreat. Many scientists have been describing the Arctic borealization, or boreal ‘Take-over’, as the transition of lower Arctic ecosystems to Boreal ecosystems, both in environmental conditions and species abundance and diversity. 

​

Nature recently published a study illustrating these changes in the marine fish communities of the Barents Sea. From 2004-2012, the temperature in the Barents Sea increased, the mixed boreal-Arctic area expanded and the sea ice decreased, leading to a shift in the distribution of fish species northwards and eastwards (shown in the figure below). The Arctic community [1], normally found in colder areas with most ice, retreated and was confined to the northernmost areas of the study, moving 159 km north. At the same time, the Atlantic shallow sub-community, previously located in the warmest regions, moved 141 km. In terms of abundance, most Atlantic species increased their numbers whereas the opposite was verified for Arctic species.

The top panels show the water masses and ice extent in (a) 2004 and (b) 2012: Atlantic Water in red (T >2ºC), Arctic Water in blue (T < 0ºC) and mixed-water masses in yellow (0ºC < T < 2ºC). The bottom panels show fish communities in (c) 2004 (d) and 2012: Atlantic in red, Arctic in blue and Central communities in yellow. Circles represent shallow sub-communities and triangles are deep sub-communities.

The pace of these range shifts is quite fast, especially compared to the global average predicted as 40 km per decade. The consequences include possible increases in predation and competition for Arctic species, that coupled with loss of habitat and food availability may have led to the observed declines in abundance. Long term, these changes in fish communities may have effects on ecosystem functioning and vulnerability.

[1] Arctic communities are dominated by bigeye sculpin (Triglops nybelini), Greenland halibut (Reinhardtius hippoglossoides) and snailfish (Liparis spp.) while Atlantic shallow commiunities are dominated by rough dab (Hippoglossoides platessoides), cod (Gadus morhua) and haddock (Melanogrammus aeglefinus).

​

——–

Sources: Fossheim M, Primicerio R, Johannesen E, et al (2015) Recent warming leads to a rapid borealization of fish communities in the Arctic. Nature 5:673–678. doi: 10.1038/NCLIMATE2647

Author: Sara Pedro

Share