Climate-driven regime shifts in Arctic marine benthos

Abstract

Climate warming can trigger abrupt ecosystem changes in the Arctic. Despite the considerable interest in characterizing and understanding the ecological impact of rapid climate warming in the Arctic, few long time series exist that allow addressing these research goals. During a 30-y period of gradually increasing seawater temperature and decreasing sea ice cover in Svalbard, we document rapid and extensive structural changes in the rocky-bottom communities of two Arctic fjords. The most striking component of the benthic reorganization was an abrupt fivefold increase in macroalgal cover in 1995 in Kongsfjord and an eightfold increase in 2000 in Smeerenburgfjord. Simultaneous changes in the abundance of benthic invertebrates suggest that the macroalgae played a key structuring role in these communities. The abrupt, substantial, and persistent nature of the changes observed is indicative of a climate-driven ecological regime shift. The ecological processes thought to drive the observed regime shifts are likely to promote the borealization of these Arctic marine communities in the coming years.climate change | community structure | ecological dynamics | ecological interactions | tipping point C limate warming has accelerated over the past 30 y, causing increases in global surface temperatures of about 0.2°C per decade (1). The greatest changes have been recorded in the Arctic, where the temperatures have risen at twice the global average rate and sea ice cover, at the end of the Arctic summer, has declined by 30% (2). These changes modify Arctic marine habitats with respect to light and temperature regimes, which, in turn, impact local biological communities (3, 4). The increasing length of the ice-free season (5), extending the period of primary production, and the increasing seawater temperature, have strong impacts on abundances and distributions of species mediated by changes in demographic and interaction parameters.

Disturbance effects of kelp thalli on structure and diversity of a coastal Arctic marine soft-bottom assemblage

“…This will very likely apply to a future Arctic, because non-calcified seaweeds are predicted to find improved growth conditions in a more acidic and warmer ocean, especially where herbivorous fish are scarce (Harley et al 2012). The observed increase in the abundance of erect red and brown seaweeds in Kongsfjord during the last two decades of warming seawater corroborates this prediction (Kortsch et al 2012). A warmer Arctic will also result in a reduced extent of protective sea ice, which may cause high algal detachment rates especially from winter storms (see references in Renaud et al 2008).…”

“…A warmer Arctic will also result in a reduced extent of protective sea ice, which may cause high algal detachment rates especially from winter storms (see references in Renaud et al 2008). A climate change induced increase in seaweed abundance (Kortsch et al 2012) in combination with higher rates of wave-induced kelp detachment will likely become challenging drivers of growing importance of seaweed-mediated disturbance of Arctic soft-bottom community structure and diversity, with yet unknown effects on the functionality in these communities.…”

“…Moreover, warming-induced loss in sea ice earlier to summer solstice has the potential to cause extensive ecological regime shifts due to light-driven tipping points, which may alter dark-adapted communities into those dominated by primary producers (Clark et al 2013). Indeed, increased kelp production and extension of kelp beds to greater depth have been reported where the period of sea ice cover has shortened (Kortsch et al 2012;KrauseJensen et al 2012;Krause-Jensen and Duarte 2014). Thus, besides more storm effects there will be also more kelp biomass exposed to waves, suggesting an increase in the relevance of disturbance from stationary and drifting kelp, particularly in the coastal areas of a warmer Arctic.…”

Range extension of a boreal amphipod Gammarus oceanicus in the warming Arctic

“…The most notable were the discovery of the thermophilic bivalve Mytilus edulis population in Isfjorden (Berge, Johnsen, Nilsen, Gulliksen, & Slagstad, 2005) and the appearance of Atlantic cod, mackerel, and pipefish along Spitsbergen (Fleischer, Schaber, & Piepenburg, 2007; Hopkins, 2002). Furthermore, thirty years of observations in two Spitsbergen fjords documented extensive structural changes in the rocky‐bottom communities with the abrupt increase in macroalgal cover and the simultaneous reorganization in the invertebrate assemblage as a consequence of temperature increase and fast ice disappearance (Beuchel & Gulliksen, 2008; Beuchel, Gulliksen, & Carroll, 2006; Kortsch et al., 2012; Węsławski et al., 2011). Also, the northward advance of snow and king crabs (Jørgensen, Løkkeborg, Fernö, & Hufthammer, 2007; https://www.unis.no/snow-crab-arrived/) and ornithological records of northward shifts of the nesting areas of gannets, great skuas, ravens, swans, and cormorants (Dr H. Strøm, Norwegian Polar Institute, pers.…”

Expansion of vegetated coastal ecosystems in the future Arctic

“…Hence, the Arctic Ocean contains a vast potential habitat for marine macrophytes. However, much of this potential habitat is unlikely to be occupied at present because it is permanently covered by ice, impacted by ice scouring or because dense ice cover limits the duration of the growth period (Müller et al, 2009;Kortsch et al, 2012;Krause-Jensen et al, 2012).…”