This small, flightless mountain that has colonized Signy Island in Antarctica is causing fundamental changes to the island’s soil ecosystem.
Research carried out by experts at the British Antarctic Survey (BAS) in collaboration with the University of Birmingham has revealed that a non-native species of fly dramatically increases rates of plant decomposition, leading to a three to fivefold increase in soil nitrate levels compared to in situ sites. Where only domestic invertebrates are found.
The study published in the journal Soil biology and biochemistrywas part of his Ph.D. The project was jointly completed by Dr Jesamine Bartlett of Birmingham and BAS, and shows how the fly, Eretmoptera murphyi, is altering soil ecosystems on the island. The insect is a decomposer, feeding on dead organic matter across the island which releases large amounts of nutrients into the soil.
Dr. Bartlett, the study’s lead author, says, “Antarctic soils are nutrient-limited systems because decomposition rates are so slow. The nutrients are there, but it took this gaseous incursion to unlock them on Signy Island. They ‘engineer the ecosystem’ in a similar way to earthworms in temperate soil systems.” .”
Eretmoptera murphyi is a native of South Georgia – an island in the Subantarctic region. It was introduced to Signy Island by chance during a botany experiment in the 1960s, though its spread only became apparent during the 1980s. Prior to this, the only terrestrial sites in Signy with high trophic levels were those associated with marine species coming ashore, for example penguin and seal colonies.
The level of nitrate measured in soil colonized by Eretmoptera was similar to the level found near seal strings, although the mounds are only a few millimeters in size. This is because the population density of fly larvae can reach more than 20,000 individuals per m2 on some sites.
Spread by humans, mostly by riding on the soles of the shoes of researchers and tourists, the hills have gradually expanded the area they colonized on the island. It can even survive in seawater for periods of time, which leads to speculation that it may eventually reach other islands.
Professor Peter Convey, Terrestrial Ecologist at BAS, says, “A particular feature of Antarctica is that it has had very few invasive species so far, and protecting this ecosystem is a very high priority. While at some level there is a lot of awareness of the implications On species invasiveness, this research really highlights how even the smallest of animals can have a very big impact.”
The hostile Antarctic environment is a significant barrier for this invasive species with extremely low temperatures, humidity, and nutrient availability. Along with the higher temperatures in the area, the nutrients the midges release will start to let in more of these invaders.
Dr Scott Hayward, an ecologist at the University of Birmingham and co-author says, “The activity of midges on Signy, combined with climate change, has the potential to ‘open the door’ for other species to become established which could further accelerate climate change. Enjoy this series.” With the ability to survive in many Antarctic sites, monitoring the spread and impacts on Signy is vital to our understanding of other Antarctic ecosystems.”
Jesamine C. Bartlett et al, Environmental consequences of a single species introduced to Antarctica: terrestrial effects of the invasive fly Eretmoptera murphyi on Signy Island, Soil biology and biochemistry (2023). DOI: 10.1016/j.soilbio.2023.108965
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