Major Expansion of Marine Forests in a Warmer Arctic

Abstract

Accelerating warming and associated loss of sea ice are expected to promote the expansion of coastal marine forests (macrophytes) along the massive Arctic coastlines. Yet, this region has received much less attention compared to other global oceans. The available future projections of Arctic macrophytes are still limited to few species and regions, and mostly focused at lower latitude ranges, thus precluding well-informed IPCC impact assessments, conservation and management. Here we aim to quantify potential distributional changes of Arctic intertidal and subtidal brown macroalgae and eelgrass by the year 2100, relative to present. We estimate habitat suitability by means of species distribution modeling, considering changes in seawater temperature, salinity, nutrients and sea ice cover under two greenhouse gas emission scenarios, one consistent with the Paris Agreement (RCP 2.6) and the other representing limited mitigation strategies (RCP 8.5). As data on substrate conditions do not exist, the models were restricted to the depth range supporting Arctic macrophytes (down to 5 m for eelgrass and 30 m for brown macroalgae). Models projected major expansions of Arctic macrophytes between 69,940 and 123,360 km2, depending on the climate scenario, with polar distribution limits shifting northwards by up to 1.5 latitude degrees at 21.81 km per decade. Such expansions in response to changing climate will likely elicit major changes in biodiversity and ecosystem functions in the future Arctic. Expansions are, however, less intense than those already realized over the past century, indicating an overall slowing down despite accelerated warming as habitats become increasingly occupied.

The invasive alga Gracilaria vermiculophylla in the native northwest Pacific under ocean warming: Southern genetic consequence and northern range expansion

“…The northwest Pacific, comprising both cold-and warmtemperate marine biogeographic provinces (Briggs and Bowen, 2012), is a global seaweed biodiversity hotspot with high species richness and endemism (Keith et al, 2014;Fragkopoulou et al, 2022). For example, approximately 1500, 1300 and 900 species of seaweeds have been reported in Japan, China and Korea, respectively (Ding et al, 2011;Kim et al, 2013;Yoshida et al, 2015), including 515 endemics in the Southern South China Sea and 85 endemics in the Jeju Island (Lee, 2008;Ding et al, 2011).…”

“…Fucus vesiculosus, Nicastro et al, 2013;Fucus guiryi, Lourenco et al, 2016). Furthermore, species distribution models (SDMs) progressively forecast that ocean warming will cause severe contractions at species' rear edges of distribution and poleward expansions (Jueterbock et al, 2013;Neiva et al, 2015;Song et al, 2021;Assis et al, 2022). This warming-induced range shift of seaweeds also stimulated a few parallel studies in the northwest Pacific and south Pacific.…”

Limited recovery following a massive seagrass decline in subarctic eastern Canada

“…Although most seagrass research has been focused in temperate and tropical regions, subarctic and arctic seagrasses are known to be important contributors to productivity, biodiversity, and human subsistence in these cold‐water coastal ecosystems (Murphy et al, 2021). Eelgrass ( Zostera marina ) is the most widely distributed seagrass species in the Northern Hemisphere and is found in the arctic and subarctic coastal regions (Assis et al, 2022; Short et al, 2007). This species has high light requirements (Léger‐Daigle et al, 2022; Wong et al, 2021), grows better in oligotrophic oxygenated waters (Zharova et al, 2001), and can adapt to a variety of conditions, with meadows being annual, perennial, or a combination of both (Murphy et al, 2021; O'Brien et al, 2018).…”

“…The recovery capacity of eelgrass is higher than persistent seagrass species (e.g., the genera Posidonia and Ehhalus ) but lower than fast‐growing colonizing species (e.g., the genera Ruppia and Halophilia ) (O'Brien et al, 2018) and varies along a latitude gradient, with northern cold‐water populations having slower leaf turnover than warm‐water populations (Clausen et al, 2014; Olesen et al, 2015). Some arctic eelgrass meadows have expanded over the past century, possibly due to increases in water temperatures (Assis et al, 2022; Krause‐Jensen et al, 2020) combined with minimal anthropogenic impacts in many but not all northern regions. Recent declines of northern eelgrass populations in the Baltic Sea were linked to water quality degradation (Boström et al, 2014).…”

Climate‐driven shifts in kelp forest composition reduce carbon sequestration potential

“…The extent of the implications of such changes on a global scale remains doubtful, particularly due to uncertainty surrounding future kelp distribution in the Arctic under different climate change scenarios. If the total area of kelps across the Arctic maximally increases by 118,500 km 2 (Assis et al, 2022), hempisphere‐scale kelp CSP might actually stay stable or increase. This scenario is imaginable since L. hyperborea and L. digitata and their arctic congener Laminaria solidungula , the CSP of which is unknown, could expand their ranges poleward, potentially mitigating or overcompensating the loss of trailing edge populations.…”