Cascading impacts of invasive New Zealand flatworms on soil food webs and ecosystem functions

Overview

The health of our soils is vital for the sustainable delivery of a wide range of ecosystem services such as food and fibre provision, carbon sequestration, habitat support, flood prevention and detoxification. The ability of our soils to perform the functions that support these services is underpinned by complex relationships between the diversity and activity of the soil’s biological community and the soil’s physical structure(1). New Zealand flatworms (Arthurdendyus triangulates) are thought to have arrived in the UK in horticultural imports sometime in the 1960’s and were first identified at the Edinburgh Botanical Gardens. Over recent decades this non-native flatworm species has been identified in gardens, allotments, and agricultural grasslands across large parts of northern England, Scotland and N Ireland(2). They are known to be voracious predators of native earthworm species and in particular impact on deep-dwelling anecic species such as Lumbricus terrestris and Apporrectodea longa(3,4) and thus, New Zealand flatworms are listed by the EU, DEFRA and the Scottish Government as an invasive non-native (alien) animal species of concern.

Despite decades of research, and the documented impact of this invasive species on native earthworm populations, their potentially cascading impacts on wider soil ecology and soil structure are less well understood. Evidence of their impact on soil functions such as hydrology and organic carbon and nutrient cycling has tended to be anecdotal and mechanistic links assumed based on the intimate relationship between soil ecology, soil structure and soil biochemical processes. It has been noted for example that Scottish pasture fields infested with New Zealand flatworm were often covered in rushes and more prone to waterlogging, presumably because of impact on soil structure and porosity(3). However, beyond the documented impacts on specific earthworm species the impacts on the functional soil biodiversity may be less pronounced due to niche filling by other species(5), and the effects of the flatworms themselves on soil structure and biochemical processes have not been determined. The impacts on soil function therefore may be more complex than has been assumed.

A. triangulates is one of more than 20 flatworm species known to be in the UK, of which only four are native, and concerns persist over the potential for climate change to assist the spread and colonization by further species such as the New Guinea flatform (Platydemus manokwari)(6) or the South American Obama nungara(7). Thus, developing a better understanding of how our soil communities are already changing in response to flatworms, and the consequences for how our soils function, is vital.

This project will explore the impacts from micro-scale to landscape scale of New Zealand flatworm on soil ecology, soil structure and soil function, seeking to better understand the interactions and drivers of changes in soil function. This will inform management and policy concerning invasive soil fauna and enable improved modelling of soil functioning in response to likely ecological change.

Methodology

This study will seek to explore the distribution of New Zealand flatworm s and their impacts in grasslands across N England and Scotland from the landscape to microscopic scale s. The project will include three study elements:
1) Field survey of agricultural grassland sites in N-S and E-W transects across N England and Scotland will update our knowledge of the distribution of the species and environmental and geographic controls on their spread . Where possible we will draw on existing national and community-project data to provide baseline data and ensure comprehensive geographical coverage.
2) Field scale studies of agricultural grasslands known to be infested with New Zealand flatworms will involve the manipulation of populations of anecic earthworms and New Zealand flatworms through selective removal to demonstrate the impact of New Zealand flatworms on not only earthworm populations, but also on the wider soil macro and meso fauna community and soil biological activity. Changes in soil structure, infiltration and water-holding capacity, SOM and soil nutrient dynamics will be used to assess impacts on soil function.
3) Mesocosm experiments will allow the impacts of New Zealand flatworm on soil structure, soil organic matter and soil nutrient cycles under controlled conditions to support the field-scale studies helping identify specific drivers of change in soil function.

The methodological toolkit used will include soil micromorphology, SEM-EDX, soil physical and chemical analysis, soil respiration and biological activity, and MicroResp for measures of carbon substrate utilisation. We will also apply for funding for isotopic analysis through NERC’s National Environmental Isotope Facility (NEIF).

Project Timeline

Year 1

Research training and methodological planning, Large-scale field survey, identification and establishment of experimental field plots. Analysis of soil communities and first data from field survey. Ecological and lab analysis training. By the end of year 1 the first chapter , including a detailed literature review, will be drafted and sample and data analysis will have begun.

Year 2

Year 2 will focus on sampling and analysis of experimental field plots and establishment of the mesocosms with training in appropriate analytical and communication skills provided as necessary. Survey data processing will produce the first results to develop a manuscript for submission and generate specific hypotheses for testing in Year 3.

Year 3

Year 3 will complete the soil and data analyses, finalising field and mesocosm experiments, targeted assays for hypothesis testing. Data analysis will provide results for presentation at international conferences such as Eurosoil 2024 and for the preparation of results chapters.

Year 3.5

Time to finalise and submit the thesis and focus on dissemination of results through conference presentations, workshops and published papers.

Training
& Skills

This project will include training in a range of specific ecological, soil, and analytical skills including: field description and sampling of soils, soil faunal identification, soil micromorphology and microanalysis, laboratory based chemical and physical analysis of soils, and statistical analysis. Training in each of these will be provided by a combination of the supervisory team and externally provided specialist training courses.

Generic, but essential, research skills (e.g. science communication, project planning and management, data analysis and presentation) will be provided through the comprehensive IAPETUS DTP training events and the Institute for Advanced Studies at the University of Stirling. The student will also be expected to participate in annual post-graduate research seminars and to present their work externally at national and international conferences.

References & further reading

1. Lavelle, P., Decaëns, T., Aubert, M., Barot, S., Blouin, M., Bureau, F., Margerie, P., Mora, P., Rossi, J.-P. (2006) Soil invertebrates and ecosystem services. European Journal of Soil Biology, 42 (S1), S3-S15.
2. Boag, B., Deeks, L., Orr, A., Neilson, R. (2005) A spatio-temporal analysis of a New Zealand flatworm (Arthurdendyus triangulates) population in western Scotland. Annals of Applied Biology, 147, 81-88.
3. Jones, H.D., Santoro, G., Boag, B, Neilson, R. (2006) The diversity of earthworms in 200 Scottish fields and the possible effect of New Zealand flatworms (Arthurdendyis triangulates) ib earthworm populations. Annals of Applied Biology, 139, 75-92.
4. Murchie, A.K., Gordon, A.W. (2013) The impact of the ‘New Zealand flatworm’, Arthurdendyus triangulatus, on earthworm populations in the field. Biological Invasions, 15, 569-596.
5. Keith, A.M., Boots, B., Stromberger, M.E., Schmidt, O. (2018) Consequences of anecic earthworm removal over 18 months for earthworm assemblages and nutrient cycling in a grassland, Pedobiologia – Journal of Soil Ecology, 66, 65-73.
6. Justine, J.-L., Winsor, L., Gey, D., Gros, P., Thévenot, J. (2014) The invasive new guinea flatworm platydemus manokwari in France, the first record for Europe: Time for Action is now. PeerJ, 2014(1), 297.
7. Negret, L., Francavilla, M.L., Damborenea, C., Brusa, F. (2020) Trying to take over the world: Potential distribution of Obama nungara (Platyhelminthes: Geoplanidae), the Neotropical land planarian that has reached Europe. Global Change Biology, 26, 4907-4918.

Further Information

Please contact: Dr Clare Wilson, Biological and Environmental Sciences, c.a.wilson@stir.ac.uk

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