Sea ice and substratum shape extensive kelp forests in the Canadian Arctic

Abstract

The coastal zone of the Canadian Arctic represents 10% of the world’s coastline and is one of the most rapidly changing marine regions on the planet. To predict the consequences of these environmental changes, a better understanding of how environmental gradients shape coastal habitat structure in this area is required. We quantified the abundance and diversity of canopy forming seaweeds throughout the nearshore zone (5 - 15 m) of the Eastern Canadian Arctic using diving surveys and benthic collections at 55 sites distributed over 3000 km of coastline. Kelp forests were found throughout, covering on average 40.4 % (± 29.9 SD) of the seafloor across all sites and depths, despite thick sea ice and scarce hard substrata in some areas. Total standing macroalgal biomass ranged from 0 to 32 kg m‑2 WW and averaged 3.7 kg m‑2 (± 3.2 SD) across all sites and depths. Kelps were less abundant at depths of 5 m compared to 10 or 15 m and distinct regional assemblages were related to sea ice cover, substratum type, and nutrient availability. The most common community configuration was a mixed assemblage of four species: Agarum clathratum (14.9% ± 12.0 SD), Saccharina latissima (13% cover ± 14.7 SD), Alaria esculenta (5.4% ± 1.2 SD), and Laminaria solidungula (3.7% ± 4.9 SD). A. clathratum dominated northernmost regions and S. latissima and L. solidungula occurred at high abundance in regions with more open water days. In southeastern areas along the coast of northern Labrador, the coastal zone was mainly sea urchin barrens, with little vegetation. We found positive relationships between open water days (e.g., without sea ice) and kelp biomass and diversity, suggesting kelp forests could increase, and their species composition could shift, as sea ice diminishes in some areas of the Eastern Canadian Arctic. Our findings demonstrate the high potential productivity of this extensive coastal zone and highlight the need to better understand the ecology of these systems and the services they provide.

Kelp in the Eastern Canadian Arctic: Current and Future Predictions of Habitat Suitability and Cover

“…This is in agreement with other studies showing that temperature is one of the main predictors that contribute significantly to explaining kelp distribution (Assis et al, 2016;Jayathilake and Costello, 2020;Krause-Jensen et al, 2020). Kelps are sensitive to warming temperatures, which can often be a stressor at warm range edges along temperate coasts (Duarte et al, 2018;Wernberg et al, 2018;Filbee-Dexter et al, 2021), and we have shown that, in our study, L. solidungula was the species with the greatest sensitivity to higher temperatures (which translates later into the species having the highest predicted loss in area). However, many kelp species in the Arctic experience temperatures close to their lower thermal limit and demonstrate improved recruitment and growth under 1-3 • C increases (Filbee-Dexter et al, 2019).…”

“…Previous and recent research campaigns across the Eastern Canadian Arctic (Filbee-Dexter et al, 2021) collected kelp cover data that allow habitat suitability and percent cover of kelp species to be modeled and predicted throughout this region. Abundance of kelp can be measured in several ways, with biomass per area, number of individuals per area (i.e., density) and percent cover being the three most common.…”

Arctic marine forest distribution models showcase potentially severe habitat losses for cryophilic species under climate change

“…The importance of sea‐ice in modelling Arctic kelp distributions is also reported by Goldsmit et al (2021). It can be expected, however, that contemporary marine forests at the highest latitudes are extremely patchy, persisting only where the ebb and flow of sea ice dynamics facilitate a brief growing season, and frequently occurring at low per area biomasses, depth ranges, and cover compared to marine forests at lower latitudes (Filbee‐Dexter et al, In press; Krause‐Jensen et al, 2012). Diminutive, poorly studied, and potentially more resilient alternate life‐history stages (e.g.…”

“…On the contrary, our decision to mask the environmental layers for depositional versus erosional shorelines may have underestimated the amount of Arctic habitat available to marine forests. The northern shorelines of Alaska, which were mostly excluded from our models, are known to host patches of marine forests interspersed among sediment‐laden bays (Wilce & Dunton, 2014), and substrate requirements may be less strict in some species (i.e., Lee (1973) reports on seemingly healthy unattached communities in calm bays, whilst Filbee‐Dexter et al (In press) show that kelp forests in the East Canadian Arctic are also present in sedimentary habitats).…”

“…clathratum and L . solidungula , were compiled from museum data records of kelp specimens from the National Herbarium of Canada at the Canadian Museum of Nature (CANA) together with data collected directly from research campaigns across the Eastern Canadian Arctic by taking pictures and videos of quadrats whilst diving (Filbee‐Dexter et al, In press). Biodiversity databases such as the Global Biodiversity Information Facility (GBIF ‐ http://www.gbif.org, accessed March 9th, 2020) and the Ocean Biodiversity Information System (OBIS; https://obis.org/) were further used for the two species of kelp (accessed 18 March 2020) and H .…”