Mechanistic model identifies increasing light availability due to sea ice reductions as cause for increasing macroalgae cover in the Arctic

Abstract

In the Arctic, rising seawater temperatures and increasing underwater light caused by reductions in sea ice cover are expected to change the structure of arctic marine communities. Substantial, sometimes sudden, increases in macroalgal productivity and biomass have already been observed in arctic rocky bottom communities. These macroalgal responses have been attributed to increasing temperature and light, but the relative importance of the suggested drivers of change has not yet been assessed. In this study, we used a mechanistic competition model to unravel the effects of temperature and light on benthic community structure and algae dominance, focusing on key algae species: red calcareous algae and macroalgal fronds. We find that light is the primary driver of increases in macroalgal coverage, whereas increased seawater temperature plays a secondary role. Shifts leading to macroalgae dominated communities may be mediated by competitive interactions, and are likely due to three light‐related processes: earlier sea ice break‐out at high latitudes can result in an exponential increase in the cumulative amount of light that enters the water column during a year; threshold effect in light requirements for algal growth; and light requirements of calcareous algae being substantially lower than those of macroalgae. With continued warming, our modeling results suggest that reduced sea ice coverage and increased light availability will favor dominance of macroalgae, which due to their key ecological role are expected to alter the structure and functioning of arctic rocky bottom ecosystems.

Reindeer turning maritime: Ice‐locked tundra triggers changes in dietary niche utilization

“…, Scherrer et al. ). In coastal tundra areas, the reindeer use of such allochthonous resource subsidies from the marine system may not only represent an increasingly important lifeline to prevent starvation at the individual level, but also contribute to the altered interactions and energy fluxes between marine and terrestrial ecosystems.…”

Arctic coastal benthos long-term responses to perturbations under climate warming

“…The fast reorganization of invertebrate communities following the sudden increase of macroalgae stands in stark contrast to the slow recolonization rates that followed the pulse perturbation in 1980. The rise in foliose macroalgae, registered in the years 1995 and 2000 in Kongsfjorden and Smeerenburgfjorden, respectively, has been linked to climate-driven reduction in sea ice cover and altered underwater light regimes [7,69]. Macroalgae facilitate benthic organisms by providing food, structural support and shelter, but can also inhibit other taxa by altering the light regime [11,13].…”

30 years revisit survey for long-term changes in the Antarctic subtidal algal assemblage

“…In most of the sites, notable pattern in the macroalgal assemblage over the last 30 years was the complementary increase or decrease of the Desmarestia complex and Himantothallus grandifolius populations which have the highest biomass in the Antarctic region and dominate in the sublittoral zone 18,29,30 ( Table 2). The complementary change and abundance shift can be interpreted in terms of temperature and inter-specific competition.…”