Biological toxins and E.coli bacteria
22 February 2019
Dr Jamie Shutler, from the University of Exeter, explains the development of biological toxin and E.coli models to help forecast low water quality events.
The accumulation of biological toxins and bacteria within farmed shellfish can cause the temporary closure of a shellfish site. Shellfish are filter feeders, so they filter water and extract food from the water making them sensitive to changes in the local water quality. The accumulation of biological toxins is completely natural and results from the shellfish feeding on specific types of naturally occurring phytoplankton. Elevated levels of E.coli bacteria can exist in the water that the shellfish filter and these can then stay within the shellfish. The elevated E.coli levels within coastal waters can be due to run off from the land from surface drains, livestock farms and untreated sewage, a situation that is often exacerbated by sudden periods of high rainfall. The shellfish themselves are unharmed by this accumulation, but harvesting and consumption during these periods can be harmful to human health. The solution is simple; harvesting is halted until the toxins and bacteria have washed through the shellfish and then harvesting can safely begin again.
The first ShellEye project developed simple numerical methods to understand how the local environmental conditions around a farm can influence and alter the water quality within the farm waters. To achieve this the project team designed and deployed a low cost monitoring buoy within an offshore shellfish farm and an estuary farm site (Schmidt et al., 2018a). Extensive analysis of historical environmental data then allowed the conditions in both farm sites to be understood (Schmidt et al., 2018b).
This work confirmed that local environmental conditions, like rainfall, sea state and sunlight, were linked to changes of water quality within the farms for both toxins and E.coli (Schmidt et al., 2018). For toxins, the work also highlighted that simple methods for monitoring the in-water conditions were key to predicting the growth of the naturally occurring, but toxin producing, phytoplankton that the shellfish then ate. The low-cost buoy was one method to detect this stratification that the phytoplankton desire (Schmidt et al., 2018b), and the subsequent increased turbidity that caused the dispersion of the phytoplankton.
This work allowed the second ShellEye project to provide weekly bulletins to a local shellfish farmer, with the aim of forewarning them (3-4 day advance warning) of changes to toxin levels within their shellfish, whilst the shellfish were still in the water.
The most recent work, in conjunction with a European Marine Fisheries Fund project (European Union funded), is now investigating how low-cost hand held instruments, that can be easily deployed from the deck of a farm boat, can be used to profile the water within the farm. These then provide an instant confirmation of the conditions within the farm waters, indicating whether or not the conditions are suitable for toxin producing phytoplankton to grow. The farmers involved in this work have found the profiles very useful and the work is continuing.
Schmidt W., Evers-King H.L., Campos C.J.A., Jones D.B., Miller P.I., Davidson K., Shutler J.D. (2018a). A generic approach for the development of short-term predictions of Escherichia coli and biotoxins in shellfish. Aquaculture Environment Interactions, 10, 173-185.
Schmidt W., Raymond D., Parish D., Ashton I., Miller P.I., Campos C.J.A., Shutler J. D. (2018b). Design and operation of a low-cost and compact autonomous buoy system for use in coastal aquaculture and water quality monitoring. Aquacultural Engineering, 80C, 28-36.