Abstract
Climate change is transforming marine ecosystems through the expansion and contraction of species’ ranges. Sea ice loss and warming temperatures are expected to expand habitat availability for macroalgae along long stretches of Arctic coastlines. To better understand the current distribution of kelp forests in the Eastern Canadian Arctic, kelps were sampled along the coasts for species identifications and percent cover. The sampling effort was supplemented with occurrence records from global biodiversity databases, searches in the literature, and museum records. Environmental information and occurrence records were used to develop ensemble models for predicting habitat suitability and a Random Forest model to predict kelp cover for the dominant kelp species in the region – Agarum clathratum, Alaria esculenta, and Laminariaceae species (Laminaria solidungula and Saccharina latissima). Ice thickness, sea temperature and salinity explained the highest percentage of kelp distribution. Both modeling approaches showed that the current extent of arctic kelps is potentially much greater than the available records suggest. These modeling approaches were projected into the future using predicted environmental data for 2050 and 2100 based on the most extreme emission scenario (RCP 8.5). The models agreed that predicted distribution of kelp in the Eastern Canadian Arctic is likely to expand to more northern locations under future emissions scenarios, with the exception of the endemic arctic kelp L. solidungula, which is more likely to lose a significant proportion of suitable habitat. However, there were differences among species regarding predicted cover for both current and future projections. Notwithstanding model-specific variation, it is evident that kelps are widespread throughout the area and likely contribute significantly to the functioning of current Arctic ecosystems. Our results emphasize the importance of kelp in Arctic ecosystems and the underestimation of their potential distribution there.
Highlights
Kelp forests dominate shallow rocky coasts in cold-water regions (Wernberg et al, 2019)
Using a combination of these two modeling approaches, this paper aims to identify the primary environmental drivers and make spatial predictions of habitat suitability and cover of kelps in the Eastern Canadian Arctic under current conditions and a future extreme climatechange scenario
Looking at response curves of environmental variables across all species for ensemble models, the most notable link between variable importance in habitat suitability for L. solidungula is that it decreases at a slower pace in regions of greater ice thickness and is less tolerant to higher temperatures (Figure 3A)
Summary
Kelp forests dominate shallow rocky coasts in cold-water regions (Wernberg et al, 2019). In the Arctic, the loss of sea ice (and increased light availability) and warming temperatures are predicted to increase the geographic extent and depth range of marine vegetation, with 145,093 km of suitable habitat projected for this type of species (Krause-Jensen et al, 2020). Coastal erosion from melting sea ice, fragmenting permafrost, and unusually high glacial inputs are, increasing sediment loads and freshwater inputs in high-latitude coastal zones (Fritz et al, 2017), which could result in direct kelp die-offs (Konar et al, 2017; Filbee-Dexter et al, 2019) or offset positive impacts of increased light and warmer temperatures (Bonsell and Dunton, 2018). The degree to which these changes will positively affect kelps will likely vary regionally, and depend on the extent of glacial ice melt, permafrost collapse, turbidity increase, and salinity reductions in coastal areas (Bartsch et al, 2016; Bonsell and Dunton, 2018; Traiger and Konar, 2018)
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