Research by experts at the University of Birmingham in collaboration with the British Antarctic Survey has revealed that a non-native midge species is significantly increasing rates of plant decomposition, resulting in three to five-fold increases in soil nitrate levels compared to sites where only native invertebrates occur.
The paper, published in Soil Biology and Biochemistry, was part of a PhD project completed by Dr Jesamine Bartlett in Dr Scott Hayward's lab within the School of Biosciences at Birmingham, and outlines how the midge, called Eretmoptera murphyi, is altering soil ecosystems on the island.
Dr Bartlett explained: "Antarctic soils are very nutrient limited systems because decomposition rates are so slow. The nutrients are there, but it has taken this invasive midge to unlock them on Signy Island. It is an 'ecosystem engineer' in a similar way to earthworms in temperate soil systems.
Dr Hayward Added: Up until now, low nutrient availability has been as much of a barrier to the establishment of certain terrestrial species in Antarctica as low temperatures or low moisture availability. So the activity of Eretmoptera on Signy, in combination with climate change, potentially 'opens the door' for other species to become established which can further accelerate ecosystem change.
Eretmoptera murphyi, is a native of South Georgia - an island in the sub-Antarctic region. It was introduced to Signy Island by accident during a botany experiment in the 1960s, although its proliferation only became apparent during the 1980s. Prior to this, the only terrestrial sites on Signy with high nutrient levels were those associated with marine species coming ashore, for example penguin colonies and seal wallows.
The level of nitrates measured in soil colonised by Eretmoptera was comparable to that found close to seal wallows, despite the midge being only a few millimetres in size. This is because population densities of midge larvae can reach in excess of 20,000 individuals per m2 at some sites.
Spread by humans, mostly by hitching a ride on the soles of boots of researchers and tourists, the midge has gradually expanded the area it has colonised on the island. It can even survive in sea water for periods of time, leading to conjecture that it could eventually reach other islands.
Dr Hayward said: "Physiologically, Eretmoptera has the capacity to survive in many other locations in Antarctica, so monitoring its spread on Signy, and associated ecosystem impacts is important and remains part of our ongoing research."
Professor Peter Convey, of the British Antarctic Survey, added: "A particular feature of the Antarctic is that it has had very few invading species so far and protecting this ecosystem is a very high priority. While at some level, there's plenty of awareness of the implications of invading species, this research really highlights how the tiniest of animals can still have a hugely significant impact."
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