South Orkneys fertilized by a midge larva | Polarjournal
These larvae will once turn into midges able to live on cold soils with an average temperature of about 2°C. Image: Chris Gilbert

The soil of an island, not far from the Antarctic Peninsula, is the scene of a powerful metamorphosis. An insect larva introduced by humans produces minerals useful to fungi and plants.

Signy Ilsand belongs to the subantarctic archipelago of the South Orkney Islands. This piece of land is home to an introduced species, native to South Georgia and which arrived in the 1960s. This species, a midge named Eretmoptera murphyi, does not fly, but it is active enough to change the nature of the soil. In 2018, scientists found that the weight of all individuals of the species exceeded the weight of native arthropods at locations it colonized. The midge and its larvae made up 2 to 5 times more of the weight. This month, a study published in Soil Biology and Biochemistry shows that its larvae break down soil organic matter at such a rate that the slopes adjoining the island’s science base are as concentrated in nitrogen as at any seal or petrel colonies.

Behind the British Antarctic Survey station at Factory Cove, Dr. Jesamine Bartlett of the Norwegian Institute for Nature and the University of Birmingham and colleagues measured the mineral content of the surrounding terrain. “Antarctic soils are very nutrient limited systems because decomposition rates are so slow,” says Dr. Bartlett according to the British Antarctic Survey. “The nutrients are there, but it has taken this invasive midge to unlock them on Signy Island. It is an ‘[ce moucheron] in a similar way to earthworms in temperate soil systems”

The researchers counted up to 83,000 larvae, that will later urn into the flighless midge, per square meter. They measure only a few millimeters. Introduced by scientists in the 1960s, they have spread throughout the island under the boots of mainly scientists and station personnel. The larva is capable of withstanding sea water for some time, and is able to spread to neighboring islands.

For the soil and the system, this invasion has a huge impact as the acceleration of the nitrogen cycle puts bacteria and microscopic algae at a disadvantage in favor of fungi. This could affect historical wooden buildings (see PolarJournal article on the subject), but also hit hard on other soil organisms such as native springtails and mites that feed on fungi. Yet, this fertilization could provide new grounds for native plants.

The Antarctic grass Deschampsia antarctica is a small vascular plant native to Signy and other subantarctic islands. It is also found at the Antarctic Peninsula. Image: Lomvi2

On the other hand, the ever-increasing availability of nitrogen could prove to be a major boon to other potentially introduced plant species which then turn invasive. For the time being, they are held back by the lack of fertile land. Dr. Peter Convey, ecologist and co-author of the study, notes, “This research really highlights how the tiniest of animals can still have a hugely significant impact.”

Camille Lin, PolarJournal

Link to study: Bartlett, J.C., Convey, P., Newsham, K.K., Hayward, S.A.L., 2023. Ecological consequences of a single introduced species to the Antarctic: terrestrial impacts of the invasive midge Eretmoptera murphyi on Signy Island. Soil Biology and Biochemistry 180, 108965.

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