Aquatic food security in Southern Africa: the role of invasive species


Invasive alien species are known to have negative impacts on ecosystems and livelihoods. In particular, invasive alien plants are pervasive, and their spread is accelerating. The global distribution of naturalised alien plants has recently been quantified. To date, 13,168 alien plant species are naturalised somewhere through human activity, a figure matching the native flora of Europe.

Despite increased understanding of the distribution of alien flora, existing studies fail to differentiate between aquatic and terrestrial systems. Both systems underpin food production, yet their importance varies strongly on a global scale. Awareness of the impacts of invasive alien plant species in developing nations, particularly in terrestrial systems, has grown. Within terrestrial habitats, land abandonment by rural communities due to plant invasions is increasingly common. For example, invasion by Opuntia stricta in eastern Africa has caused a 50-75% loss of grazing land and reduced health of livestock. However, little is known of the consequences of invasion by alien plants in aquatic systems, in particular on food production.

Aquatic systems perform many key ecosystem services including food production (directly or indirectly, e.g. by supplying irrigation water), but are often overlooked relative to terrestrial systems, due to constraints on data and accessibility. Previous research has shown that Africa’s most important inland fishery, Lake Victoria, which feeds 22 million people, has suffered from invasion by water hyacinth (Eichhornia crassipes). Water hyacinth mats can block light, severely reducing oxygen levels, which may affect fish communities. For fishers, the hyacinth mats have reduced their catch by covering large areas, delaying access to markets because of loss of output, increasing fishing costs because of the time and effort spent in clearing waterways and,, ultimately forcing translocation. However, the availability of data to evidence this is severely limited and the impact of aquatic invasive alien plants in these systems is thus poorly understood.

Globally, aquaculture is projected to contribute >90% of global fish consumption by 2030, raising the need for better understanding of invasions in aquatic habitats. More than 90% of global inland fish production occurs in developing countries in Africa and Asia. Where survival of local people depends on indigenous food production, invasive alien plants therefore pose a major threat, but the scale of this threat to aquaculture production has yet to be quantified.

Despite being land-locked, Malawi has substantial freshwater resources. Twenty percent (24,405 square kilometres) of Malawi’s total area is covered by freshwater mainly in the form of Lakes Malawi, Malombe, Chilwa and Chiuta. These lakes, together with the Upper and Lower Shire River, provide the majority of Malawi’s fish resources. Malawi has historical associations with capture fisheries, and fish is an important component of the daily diet for Malawians. For many poorer families fish is the only regularly available source of animal protein. Therefore, any threat to fish capture, direct or indirect, will have negative consequences for food security and health.

The overall aim of this project is to better understand the impact of invasive alien plants on aquatic food security using Malawi as a case study. Specifically, the project objectives are to:

1) Undertake a baseline assessment of the impacts of invasive alien plants of freshwater systems in Malawi, to understand the potential threats to aquaculture production.
2) Use questionnaires, interviews and/or focus groups to explore known or perceived threats to fish yield.
3) Undertake a comparison study in invaded and uninvaded freshwater systems to assess differences in the environmental conditions that may be directly or indirectly driving fish yield.
4) Evaluate direct and indirect drivers of yield, undertake a future scenarios analysis to identify future threats to fishery production
5) Run a stakeholder workshop to communicate findings and raise awareness of threats to food security

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Image Captions

River in Southern Africa invaded by water hyacinth. Z Pattison


This project is interdisciplinary, utilising both environmental and social science methodologies. This combination of methodologies is commonly lacking in invasion science, offering a novel way forward to address challenges to food security from invasions.

Project objectives and how each will be addressed:
1) The student will undertake a meta-analysis of the available literature to understand the known impacts of invasive alien plants in freshwater systems. From this analysis, we will derive a list of key invasive alien plants and the threats associated with each, enabling us to prioritise a measure of risk for each species.
2) A social science study (qualitative and/ or quantitative) will be used to engage with farmers and fishers, to establish known and perceived threats to fish yield. This will give us insight into where and why inland freshwater habitats are chosen for fishing, which factors dictate those decisions and levels of awareness of invasive alien plants within the system.
3) Databases such as- Food and Agriculture Organization of the United Nations (FAO) data on fishing/aquaculture sites and Global Biodiversity Information Facility (GBIF) – will be used to identify whether an invasive alien plant is present, suitable field sites will be identified to compare the impacts of invasion on both environmental characteristics and fish yield within a site. Measurements of water quality, surrounding land use and plant communities will enable estimation of indirect drivers on fish yield, whilst fish number and biomass will be used to quantify differences in yield between invaded and uninvaded sites.
4) Understanding the direct and indirect drivers of impact on fish stocks/capture, against a background knowledge of the most impactful and/or invasive species, a scenarios analysis will be undertaken to assess future risks of invasion and how this will affect fish capture.
5) A workshop (or workshops) will be held with the key local stakeholders identified through the project (e.g. fishers, non-governmental organisations, policy makers) to feedback results from the study and explore future strategies to mitigate the impact of invasive alien plants on aquaculture production in Malawi.

Project Timeline

Year 1

Literature review as a meta-analysis (months 1-5, aiming for publication, Obj.1); start designing social science study for pilot testing (months 6-7, Ob.j 2); identify possible field sites using FAO and GBIF (month 8, Obj. 3); ground-truthing visit to Malawi to assess field site viability and identify aquaculture farm owners and fishers to run pilot study (month 9); analyse data from pilot study (months 10-12); internal/ external training (depending on the individual needs of the student)

Year 2

Build and develop on social science study (months 13-15), preparation for fieldwork (months 16); fieldwork in Malawi to assess habitat and fish capture variation between invaded and uninvaded sites (months 17-18) and undertake a social science study to understand perceived and known threats to fish capture (months19-20); scope stakeholder groups and local committees involved in fisheries; data management – collate and clean data; address training needs for data analysis (months 21-24); attendance at national conference

Year 3

Data analyses, writing up results (months 25-30); Data dissemination with stakeholder group (month 31, obj.5); attendance at an international conference; writing publications and thesis submission (months 32-42).

Year 3.5

Continued- writing publications and thesis submission (months 32-42).

& Skills

The student will receive training from an interdisciplinary supervisory team, particularly in some of the key NERC ‘most wanted’ skills:
• Multi-disciplinarity: This research is at the interface between environmental and social science. The student will receive training in working within interdisciplinary teams, and effectively communicating between disciplines.
• Freshwater science: The student will learn about freshwater ecosystems and biodiversity, gaining skills in assessing water quality metrics, species identification and understanding the importance of water resources to ecosystems and food security.
• Data management: The student will receive training in analysing a variety of data types.
• Modelling: The student will learn new and innovative modelling techniques, having the opportunity to gain expert training in meta-analysis, structural equation modelling and machine learning.
• Fieldwork: The student will receive training in undertaking participatory research with Malawian communities.
• Translating research into practice: The student will receive training in science communication to multiple audiences (e.g. policy makers, non-governmental organisations (NGOs) and the wider public), as well as understand the role of their research in working towards the United Nations Sustainable Development Goals, namely Goal 2 – Zero Hunger and Goal 14 – Life Below Water.

The student will also participate in IAPETUS training and events. A training budget is included for any external training required by the student.

References & further reading

Harrison, I.J. (2018) The freshwater biodiversity crisis. Science 362:1369.1-1369

Pattison, Z.; Minderman, J., Boon, P.J. & Willby, N. (2017) Twenty years of change in riverside vegetation: what role have invasive alien plants played? Applied vegetation science, 20: 422-434

Van Kleunen, M.; et al. (2019) The Global Naturalized Alien Flora (GloNAF) database. Ecology, 100:1

Weyl, O.L, Ribbink, A.J. & Tweddle, D. (2010) Lake Malawi: Fishes, fisheries, biodiversity, health and habitat. Aquatic Ecosystem Health and Management, 13:241-254

Willby, N. (2007) Managing invasive aquatic plants: Problems and prospects. Aquatic Conservation Marine and Freshwater Ecosystems, 17: 659 – 665


Further Information

Dr Zarah Pattison

email: .

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