How do organisms begin new life at the bare surfaces exposed by glacier retreat? A team of researchers from the Czech Republic recently published a paper on the spread of one organism, a lichen, across James Ross Island near the Antarctic Peninsula. The study found that lichens can disperse over long distances, likely by means of aerial transport. Increasing warming trends on James Ross Island will likely result in more deglaciation, providing species like lichens with the opportunity to colonize new areas.
There has previously been considerable debate on the reproductive and dispersal mechanisms of lichens, especially in the polar regions. The study’s findings on lichen reproduction is promising, given the important role lichens play as primary successors, contributing to soil development and the establishment of ecosystems with greater biomass and biodiversity. Combining an alga and a fungus, the lichen can grow on almost any surface, from sea level or high altitudes to the side of trees or on rocks. Lichens are also able to reproduce both sexually (through propagules, which are small, vegetative structures that get detached from the parent plant) or asexually (mini-lichens), and are transported by wind, sea currents or birds.
GlacierHub spoke with lead author Elster Josef from the Center of Polar Ecology about the study. He asserts that one of the most distinctive features of James Ross Island is the island’s so-called volcanic mesas, which are favorable locations for biomass growth. Volcanic mesas originate from superimposed subglacial volcanic eruptions and are characterized by a relatively flat highland with steep edges. Usnea sp., a lichen commonly known as the old man’s beard, is the most important lichen in this system. “It produces dense carpets in the oldest volcanic mesas. This species has many advantages in respect of dry local climate,” Josef said.
There is a clear gradient of lichen cover and diversity from north to south on James Ross Island, according to Josef. One important question of the research was how this lichen carpet advances with glacier retreat. Josef stated that his team was able to successfully develop a non-invasive method to measure lichen carpet diversity and biomass. Traps in the form of petri dishes fixed to rock surfaces with stick tape were the simplest and most effective way for the team to measure lichen dispersal across the island, according to Josef. A total of 100 traps were placed during the summer season of January/February 2008 and left exposed for a year. In the end, only 60 traps were found due to snow cover and strong wind disturbance.
For the Antarctic lichens, vegetative asexual reproduction was found to be more dominant due to environmental stresses. While the old man’s beard and the Leptogium fungus (Leptogium puberulum) were the two most common local species on the island, their frequency of occurrence in the traps was unrelated to local species dominance. Long-distance dispersal of vegetative parts occurs more frequently on the larger scale as a result of wind conditions.
Surface wind speeds on the mesas are often higher than 6m/s (roughly 12 mi/hr) on average, with extremes reaching up to 30m/s (60 mi/hr). Larger amounts of lichen spores and fragments were found in the traps located along the prevailing wind direction. Overall, the highest occurring species in the traps were of foliose and fruticose growth types, which favored wind dispersals.
The main difficulty of the research method was that the dispersal of lichens is influenced by many abiotic and also biotic factors, according to Josef. These include distance from glaciers and elevation to existing lichen diversity and cover on site. The method was also limited because it did not involve measurements of what is viably ready (in-situ) to start growth and only measured what types of lichens were dispersed.
The greatest confirmation to the team’s hypothesis was the strong positive correlation between the size of clast, or rock fragment, and the dispersed species assembly. Clast size is determined based on the average diameter of rocks in the area. Often, areas with larger clast size are characterized by a thriving diversity of lichen communities. They represent more stable locations for growth since larger stones shield the newly-trapped lichen fragments from being uprooted by the wind again.
Still, according to Josef, lichen development is rather rare despite the large numbers of reproductive fragments dispersed. The growth of a lichen community is a long-term process, and Josef hopes to continue to evaluate the reaction of lichens to climate change in polar regions to shed light on the colonization mechanism of pioneer species in newly-exposed surfaces.