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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead supervisor: David Aldridge, Zoology

Co-supervisor: Ed Turner, Zoology

Brief summary: 
This project will compare historical surveys with present day distributions to quantify spatial, temporal and taxonomic patterns in the overlooked but rapid disappearance of many molluscan species.
Importance of the area of research concerned: 
The rapid global decline in many invertebrate taxa, such as insects, has received considerable attention by researchers and the media. However, taxa such as molluscs have been largely overlooked. Recent studies in Europe suggest that freshwater mussel populations have declined rapidly in some locations, with >90% reductions reported from the River Thames over the past fifty years (Ollard & Aldridge, 2023). Freshwater molluscs are recognised as some of the most vulnerable taxa in the world (Bohm et al., 2021) and they provide many important ecosystem services (Zieritz et al., 2022) including ecosystem engineering that can create habitat for many other invertebrates (Chowdhury et al., 2016). It is essential that we quantify the patterns of recent declines so that drivers of loss can be identified and conservation actions can be put in place.
Project summary : 
We hold detailed, quantitative survey data on freshwater mussel populations across the UK spanning the past three decades. A number of rivers have been surveyed regularly. Data include species abundance, population structure and growth rates (as deciphered from annual growth rings). Additional datasets are held by colleagues, conservation charities and government agencies (e.g. Environment Agency), and include data on pea clams (sphaerids) and snails. By resurveying sites using the same methods as originally reported the student will be able to document, for the first time, the patterns of change in molluscan communities across the UK. Collaborations with molluscan researchers across Europe through the EU COST Action 'CONFREMUS' will help to set the findings in a wider context. Our group is currently investigating drivers of mass mortality events in mussels (Brian et al., 2021).
What will the student do?: 
The student will collate historical datasets from different sources. We already hold extensive data ourselves which will form the core of the thesis. Sites will be located and in some instances may require engagement with the original surveyors. For freshwater mussels this will involve entering rivers in a drysuit and hand sampling, or using a mussel dredge. For pea clams and gastropods this will involve standardised sampling using a hand net. Growth rates and longevity of mussels can be estimated using annual growth rings and through fitting growth models. Smaller species will be identified through microscopy. Possible drivers of decline will be investigated by non-lethal sampling of pathogens, investigating long-term datasets on water chemistry (supplied by the Environment Agency), assessment of patterns on invasive species establishment and reviews of landuse change. Are all species equally affected? Are there particular time periods of change? Are particular habitats or geographic regions more vulnerable than others? Are declines in native taxa associated with increases of particular invasive species?
References - references should provide further reading about the project: 
Ollard, I. & Aldridge, D.C. 2023. Declines in freshwater mussel density, size and productivity in the River Thames over the past half century. Journal of Animal Ecology, vol. 92, pp.112-123. DOI: 10.1111/1365-2656.13835
Böhm, M. et al. 2021. The conservation status of the world’s freshwater molluscs. Hydrobiologia, vol. 848, pp. 3231-3254.
Brian, J.I. & Aldridge, D.C. 2021. Don't move a mussel? Parasite and disease risk in conservation action. Conservation Letters, vol. 14, e12799. DOI: 10.1111/conl.12799
You can find out about applying for this project on the Department of Zoology page.