Increasing temperatures, diversity loss and reorganization of deep-sea fish communities east of Greenland

Abstract

In recent years, Arctic and sub-Arctic fish communities have shown extensive reorganization on shelves and in shallow waters, but little is known about the ecological impact of environmental changes in deeper waters. We examined temporal changes (1998-2016) in fish diversity and community structure based on research survey data from East Greenland, over a depth gradient spanning 400 to 1500 m. A northern and a southern continental slope region, 360 km apart, were analysed for temporal changes in water temperature and fish community structure. The bottom water temperature increased by up to 0.2 and 0.5°C, respectively. Contrary to expectations, there was a concomitant loss of species richness of up to 3 and 5 species, respectively, and a decrease in total abundance in both regions. Abundances of individual species displayed different trends between regions, with 3 species of wolf fishes (Anarhichas spp.) and American plaice Hippoglossoides platessoides decreasing in the north and blue antimora Antimora rostrata, Agassiz’ slickhead Alepocephalus agassizii and the roundnose grenadier Coryphaenoides rupestris decreasing in the south. The regional differences may reflect different oceanographic characteristics, as the northern region is more influenced by colder Arctic water, whereas the southern region is primarily influenced by the Subpolar Gyre (SPG). However, the observed temperature increase is expected to be due to an intensifying Atlantic Multidecadal Oscillation and/or anthropogenic climate change and not to SPG changes. The observed changes in biodiversity and community structure associated with warming are likely to affect community dynamics and alter ecosystem functioning.

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

“…These observations would suggest that increasing temperatures in deeper waters along the slope might also result in increasing species richness. However, in accordance with Emblemsvåg et al ( 2020 ), we found that the local loss of species is not compensated by the gain of species (Figure S6 ; Table S1 ), leading to a decrease in species richness. These results are likely related to regional oceanography, which generates different biodiversity trends than what is observed in other high latitude shelf seas like the Barents Sea (Fossheim et al, 2015 ; Hiddink and Hofstede, 2008 ; Johannesen et al, 2012 ).…”

“…The dominance of the cold East Greenland Current on the shelf might explain why the response of demersal communities in shallow waters was weaker. The deeper regions are under the impact of the warmer Irminger Current, which has likely caused the increase in temperatures observed along the slope (Emblemsvåg et al, 2020 ). This climate signal is largely absent on the continental shelf (Figure 5 ) and highlights the importance of considering regional and local environmental conditions in analyses and predictions of ecosystem responses to climate change.…”

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

“…A likely explanation for these observations is the lack of influence of the warm Atlantic Irminger current on the shelf, which is manly dominated by the cold East Greenland Current. Along the slope, these two currents meet and mix, with the Irminger current being the likely source of a warming trend (Emblemsvåg et al, 2020). Such fronts between different water bodies are known to create favourable environments for primary production, foraging fish, and generalist feeding behaviour.…”

“…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.…”

“…We expected a borealization of functional composition driven by increasing occurrence of boreal species. Further, the documented loss in species richness (Emblemsvåg et al, 2020) is expected to affect negatively functional diversity, raising the question of whether the addition of boreal traits can compensate for the loss of Arctic ones, thereby maintaining functional diversity. We also expected that trends in functional composition and diversity would differ between depths due to different oceanographic features and different rates of warming.…”