The Earth’s polar regions, encompassing the Arctic and Antarctic, are extreme environments characterized by frigid temperatures, vast, ice-covered landscapes, prolonged periods of darkness or continuous daylight, and limited liquid water. Despite these challenging conditions, a surprising array of plants and algae thrive, forming the foundation of polar ecosystems.
Algae of the Frozen World
Algae are pervasive in polar environments, forming a significant component of primary producers in aquatic and icy habitats. Snow algae, often responsible for the phenomenon known as “watermelon snow,” are freshwater micro-algae that grow on snow and ice surfaces. Their pigments, particularly carotenoids like astaxanthin, give the snow red, green, or orange hues, and these dark colors can reduce the snow’s reflectivity, potentially accelerating melting.
Within the sea ice itself, sea ice algae flourish in microscopic brine channels and pockets. These channels provide a sheltered, nutrient-rich environment where algae, primarily diatoms, can photosynthesize even under thick ice. Sea ice algae are among the first primary producers to become active in the polar spring, extending the productive season and forming a crucial food source for the marine food web. Cryoconite algae inhabit cryoconite holes, which are small, water-filled depressions formed on glacier surfaces by the accumulation of dark, windblown dust. These holes create distinct microbial ecosystems, where algae, bacteria, and other microorganisms thrive in the meltwater. Freshwater algae also populate melt ponds and lakes that form seasonally on ice sheets and permafrost, contributing to local aquatic productivity.
Terrestrial Flora of the Poles
On the ice-free landmasses of the polar regions, terrestrial flora is dominated by non-vascular plants, with a limited presence of flowering species. Mosses and lichens are particularly widespread and resilient, colonizing vast areas of exposed rock and thin soils in both the Arctic and Antarctic. Lichens, which are symbiotic associations of a fungus and an alga, can tolerate very cold temperatures and can even photosynthesize while frozen.
The Arctic, with its larger land area and more varied geological history, supports a greater diversity of terrestrial plants, including approximately 1,700 species of flowering plants, dwarf shrubs, herbs, and grasses. Examples include the Arctic poppy, known for its cup-shaped flowers that track the sun, and purple saxifrage, often one of the first plants to bloom. In contrast, the Antarctic continent hosts only two native flowering plant species: Antarctic hair grass (Deschampsia antarctica) and Antarctic pearlwort (Colobanthus quitensis). These low-lying plants are primarily found on the Antarctic Peninsula and its associated islands, where conditions are slightly less severe.
Thriving in Extremes
Polar plants and algae have adapted to survive their harsh environment. To cope with extreme cold, many produce cryoprotective compounds like sugars, polyols, and antifreeze proteins that prevent ice crystal formation within their cells. They can also reduce their cellular water content and undergo cold hardening processes, triggered by light and temperature changes, to increase frost tolerance.
Efficient photosynthesis at low light intensities is another common adaptation, with many species able to photosynthesize in sub-zero temperatures or under a layer of snow. Some plants possess dark pigments or cup-shaped flowers that help them absorb more solar energy. Nutrient scarcity, resulting from slow decomposition rates in cold soils, is addressed through efficient nutrient uptake and recycling, as well as symbiotic relationships, such as those seen in lichens. Dealing with water availability is also crucial, as most water is frozen. Adaptations include desiccation resistance and reliance on meltwater during brief summer thaws. Terrestrial plants often exhibit low-lying, cushion-forming growth habits, which help trap heat, reduce exposure to strong winds, and conserve moisture.
The Role of Polar Life
Polar plants and algae play a fundamental role in their respective ecosystems, serving as the foundation for complex food webs. As primary producers, they convert sunlight into organic matter, providing the initial energy source for herbivores and, indirectly, for higher trophic levels. Sea ice algae, for instance, are a significant food source for zooplankton and other marine organisms in early spring.
These organisms also contribute to global carbon cycling. Terrestrial plants in the Arctic, particularly those growing in permafrost regions, store significant amounts of carbon in the soil, preventing its release into the atmosphere. Marine algae, specifically phytoplankton, are major contributors to the ocean’s biological carbon pump, absorbing carbon dioxide from the atmosphere and sequestering it in deep ocean waters when they die and sink. Changes in the distribution, growth, or abundance of polar plants and algae can serve as indicators of broader environmental shifts, such as those driven by climate change. For example, increased growth rates of Antarctic flowering plants have been linked to rising regional temperatures.