Deep demersal fish communities respond rapidly to warming in a frontal region between Arctic and Atlantic waters

Abstract

The most prominent impact of climate warming on marine ecosystems are distributional shifts in fish, which influence species interactions and food web organization. For shallow continental shelf seas, this usually implies a poleward shift or movement to deeper waters to retreat in cold water refuges (Dahlke et al., 2018;Fossheim et al., 2015;Pinsky et al., 2013). Although more than 90% of the habitable oceans' volume lies below 200 m, long-term studies of biodiversity in slope and deep-sea regions are rare (Danovaro et al., 2020;Howell et al., 2020;Levin and Bris, 2015). It has often been proposed that the rapidity of species' responses to climate change decreases with depth because deeper waters are thermally more stable (Levin and Bris, 2015;Van der Spoel, 1994;Yasuhara et al., 2014). However, rapid responses in the abundance of deep-sea biotas, such as fish, nematodes and amphipods, to changing environmental conditions at the surface indicate that processes such as changes in primary productivity can trigger unexpectedly fast responses in the deep

Recent warming causes functional borealization and diversity loss in deep fish communities east of Greenland

“…This causes the depth profile of functional dispersion to shift from having a peak at around 900 m in 1998–2004 to an increasing trend with depth throughout the investigated depth range in 2010–2016, an outcome also influenced by species evenness increasing with depth. The transition phase in 2005–2010 is consistent with rapid changes in fish community abundances reported within this period (Emblemsvåg et al, 2022). Lower species richness and functional richness at 400 m depth in the years after 1998–2004 and the concomitant increase in these indices below 400 m depth could indicate redistribution towards deeper waters, as suggested for sub arctic species in west Greenland (Lekanda et al, 2021).…”

“…The three depth strata and time periods were based on results from Emblemsvåg et al (2022), which showed that most temporal changes in fish community structure were observed in depths between 300 and 1000 m from 2005 until 2010, whereas little temporal change was observed in the shallower and deeper strata and before 2005 or after 2010. Data were analysed using software R version 4.0.3 (R Core Team, 2020).…”

“…Models addressing temporal development were run for three depth strata (150–350 m, 350–1000 m and 1000–1500 m), and models of depth profiles for three different time periods (1998–2004, 2005–2010 and 2011–2016). The three depth strata and time periods were based on results from Emblemsvåg et al (2022), which showed that most temporal changes in fish community structure were observed in depths between 300 and 1000 m from 2005 until 2010, whereas little temporal change was observed in the shallower and deeper strata and before 2005 or after 2010.…”

“…A change in sampling time could have caused a shift in species abundances and thereby affected the results. However, after thorough checking, both descriptively and by use of statistical tests (change point analysis), we conclude that the change in survey time did not likely influence the observed changes in species composition (Emblemsvåg et al 2022). The catch was sorted, identified to the species level, weighed, and counted.…”

“…The decline in species richness in East Greenland (Emblemsvåg et al, 2020(Emblemsvåg et al, , 2022 is largely driven by benthivores with low fecundity and motility, such as eelpouts (Lycodes spp.) and wolffishes.…”