Dr David Morritt

Research interests

Overview of current research

My original work examined how invertebrate groups are adapted to stressful habitats and how they respond to environmental stresses, both natural e.g., salinity, temperature and xenobiotic e.g., pesticides, heavy metal pollutants. Other studies addressed activity patterns and adaptations to desiccation / thermal stress in highshore tropical and temperate molluscs and thermal tolerance and evolution in crustaceans associated with hot springs. My interests in aquatic pollutants have included studies on endocrine disruption in marine (bivalve molluscs) and freshwater (gammarid amphipods) invertebrates and fish; the lethal and sub-lethal effects of pesticides on freshwater midge larvae and use of probabilistic risk assessment and extrapolation between freshwater and marine toxicity data sets.

I have also collaborated with Prof. David Sims and colleagues at the Marine Biological Association, Plymouth on a NERC-funded project testing the optimal diet model in free-ranging dogfish in Lough Hyne, Ireland. We used a fully automated radio acoustic positioning (VRAP) system to monitor the movements of transmitter-tagged dogfish and relate the fine-scale movement patterns (1-2 m resolution) to potential prey availability, dietary composition and other measured environmental variables. This work has also contributed to a publication on Lévy-type foraging patterns in marine predators.

I have on ongoing collaboration with Prof. Gray Williams and Dr Kenneth Leung (The Swire Institute of Marine Science)and others on the ecology and ecophysiology of temperate and tropical intertidal invertebrates, including molluscs, crustaceans and mosquito larvae. Field and laboratory work has described the integrated physiological and sub-cellular response to different combinations of environmental stresses in the limpet Cellana grata.

Current research interests also include collaboration with Dr Paul Clark at the Natural History Museum, London on the biology of invasive (Chinese mitten crab, Eriocheir sinensis) and threatened (European eel, Anguilla anguilla) species in the River Thames and reservoirs in SE England.

Chinese mitten crabs are one of top 100 invasive species in the world and are now well-established in the Thames and certain other river catchments where they can cause damage to river banks, damage fishing gear and have an impact on native species and fisheries. Adult mitten crabs spend a number of years in the freshwater reaches of rivers but have to return to sea to breed and for females to release the larvae. Once the early developmental stages have settled out of the plankton the juvenile crabs then migrate from the estuary back up the river. Our work on mitten crabs includes monitoring of the autumn seaward migration of adult crabs at Walton-on-Thames (Thames Water) and a public recording scheme to record the distribution of Chinese mitten crabs across England and Wales (see www.mittencrabs.org.uk for further details). Current PhD students are working on developing novel imaging techniques for mitten crab larvae and also using modelling approaches to assess the impacts of mitten crabs in the Thames with particular focus on river bank erosion at selected sites, e.g. Chiswick Eyot.

A project combining both species in a fyke net study in the inner Thames estuary compared different fyke net designs. The aim of the project was to identify a fyke net design that can potentially maximise the catch of invasive Chinese mitten crabs whilst minimising the bycatch of other fish, especially undersized European eels. This study was funded by the Marine Management Organisation and the Environment Agency.

One of the unexpected outcomes of this study was the large amounts of plastic litter recovered from the fyke nets set to fish on the river bed. Publication of these results and subsequent media coverage and outreach events has led to this becoming a new focus of research collaboration with Dr Paul Clark (NHM). Not only have we documented macroplastics in the Thames but, through the studes of Alexandra McGoran, we now have increasing evidence of the presence of microplastic fibres and fragments in the guts of Thames fish. A more recent project has made a comparison with fish species in the Clyde Sea. A new PhD student, Danny Hodgson, will be developing this work further in collaboration with the FSC Millport and the NHM. Current Masters students are working on the deposition of single-use plastic water bottles on the banks of the Thames and also the presence of microplastics in the Thames water column and larval fish (in collaboration with ZSL and NHM), Data from published papers have been used to support the Port of London's Cleaner Thames campaign, Hubbub's For Fish's Sake campaign, have been presented at a All Party Parliamentary Group on Marine Litter in June 2016 and cited in a report on bottled water to the London Assembly Environment Committee. Evidence was also recently submitted to the Environmental Audit Committee inquiry into disposable drink packaging. We also contribute to the Thames Estaury Partnership Litter Forum and Marine Litter Action Network.













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