This tiny beastie does not have a common name, mostly because not many people have ever encountered it. But it is proving to be very valuable in terms of understanding how the introduction of one species can change a whole ecosystem.
The Displaced
Location and Climate
This case study takes place in a very remote location - Signy Island (Lat. 60°43'0"S, Long. 45°36'0"W) which is part of the South Orkney group of islands. This small archipelago lies off the coast of the Antarctic continent in the South Atlantic Ocean. Signy itself is about 6.5 km by 5 km and with an area of 1,926 ha. The highest point is about 280 m above sea level. About half the island is permanently covered in ice. The British Antarctic Survey maintains a research base which supports 8 to 10 people over summer.
According to https://datazone.birdlife.org/site/factsheet/signy-island-iba-antarctica
The winter climate on Signy Island is influenced by pack ice which extends to surround the island from the Weddell Sea. Over summer pack ice retreats and Signy Island has a maritime climate. Mean summer air temperatures are between –2°C to 3°C, whilst during winter the mean monthly air temperature ranges from –2°C to –17° C. Strong winds are frequent, prevailing from the west. The minimum winter temperature on record is –39.3°C, whilst in summer temperatures range from –7°C to 19.8°C.
The natives
Mosses, liverworts and lichens can grow under these circumstances and do indeed form the bulk of the flora on the island. They tend to be absent at elevations over 120m.
There are only two species of flowering plants found on the island - Antarctic Hairgrass ( Deschampsia antarctica ) and Antarctic Pearlwort ( Colobanthus quitensis ). They are both small.
Three species of penguin have breeding grounds on the island plus a number of seabirds including petrels and terns. Elephant seals also give birth along the coast.
Signy’s soils and flora are inhabited by fungi, protozoa and bacteria, plus large numbers of micro-invertebrates, including tardigrades, springtails, and nematodes .
The Misplaced
Eretmoptera murphyi is a small non-biting midge which is part of the order Diptera (flies). This species is a native of South Georgia Island– an island in the South Sandwich group in the sub-Antarctic region. It is thought to have hitched a ride on plant material relocated to Signy as part of an experiment carried out in the 1960s.
Characteristics
This non-biting midge is small, around 4 mm long and superficially resembles a mosquito. As it is an insect, its body is divided into head, thorax and abdomen. Eyes are prominent in the head and it has short antennae. The wings attached to the thorax are very short and not capable of carrying its body weight, rendering it flightless. There are 3 pairs of legs attached to the underside of the thorax.
This animal can survive limited periods of immersion in both ice and seawater.
Breeding
As shown in the image above, this midge has a 2 year life cycle, going from egg to larva to pupa to adult over that time. As an adult, it has about a 7 day life span. Eretmoptera murphyi is a parthenogenetic organism which mean that females produce eggs that develop into embryos without sperm.
Ecology
Eretmoptera murphyi's optimal temperature for activity is 4⁰C. It can survive temperatures down to -19⁰ C.
Its diet consists of dead plant (primarily moss) matter. It has no competitors for this food and no natural predators on Signy Island. Due to the cold climate, decomposition occurs very slowly and, consequently soils are mostly nutrient poor. Some nitrogen is added to the soil via the deposit of faeces by birds and seals in coastal margins. In general, growth is slow due to temperatures and low nutrient turnover which favours moss species as the dominant plants in the community. Some mossbanks are up to 2m thick and maybe 5000 years old.
The Consequences
Due to the lack of competitors and predators in the Signy Island environment, the population of this midge has soared since its accidental introduction in the 1960s. Densities of midge larvae can reach 20,000 - 100,000 individuals per m2 at some sites. It has extended its range from the immediate area around the research base station to 85,000m2. It is thought that the midge hitches a ride on human's boots to expand its range.
E. murphyi is the largest terrestrial invertebrate on the island. It now contributes substantial biomass to the local community and has had a significant effect on the rate of decomposition of plant material in the areas where it is found.
The key finding was that E. murphyi is the likely driver of an increase in inorganic nitrogen availability within the nutrient-poor soils in which it occurs. When compared with the levels of inorganic nitrogen present in soils influenced by native vertebrate wildlife aggregations, the increase in local nitrate availability associated with E. murphyi was similar to that caused by deposits from seals and giant petrel colonies. Overall, available nitrate has increased by three- to five-fold in soils colonised by the midge, relative to undisturbed soils. This may ultimately impact rates of decomposition as well as the native plant and micro-arthropod communities of Signy Island.
Significance
For the vast majority of people, this may seem distant and insignificant. However it does serve a a purpose and deserves to be examined.
Ecosystems in these small islands off the coast of Antarctica are characterised by low biodiversity and hence are the least complex systems to examine and understand how invasive species impact systems.
In the words of two scientists involved with the research
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.”
Invading insect could transform Antarctic soils
Dr. Hayward is a senior lecturer in Molecular Ecophysiology at the University of Birmingham
Professor Peter Convey is a terrestrial ecologist at The British Antarctic Survey
Stopping the spread
Given that E. murphyi is thought to be spread on human's boots and there is a standard protocol for boot biosecurity, it was necessary to test the efficacy of the currently used procedure. It was found to be ineffective and a new regime has been recommended.
Dig Deeper
- Ecological consequences of a single introduced species to the Antarctic: terrestrial impacts of the invasive midge Eretmoptera murphyi on Signy Island
- The effectiveness of Virkon® S disinfectant against an invasive insect and implications for Antarctic biosecurity practices
- Life cycle and phenology of an Antarctic invader: the flightless chironomid midge, Eretmoptera murphyi
- Biological invasions in terrestrial Antarctica: what is the current status and can we respond?
- Surviving the Antarctic Winter—Life Stage Cold Tolerance and Ice Entrapment Survival in The Invasive Chironomid Midge Eretmoptera murphyi
- Signy Island as a Paradigm of Biological and Environmental Change in Antarctic Terrestrial Ecosystems
The papers listed above can be pretty heavy going for laypeople. An alternative approach to this topic is provided by Dr. Jesamine Bartlett who carried out much of the research in this case study. She has produced a cartoon poster version.
The original full size poster can be downloaded here.
