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  • Predicting the dispersion of invasive marine species

    Dispersion of invasive species
  • Dispersion of invasive species
  • Dispersion of invasive species
  • Dispersion of invasive species
  • Dispersion of invasive species

Dispersion of invasive species

HR Wallingford’s team of ecological modellers completed a study to predict the ability of the manila clam larvae, an invasive marine species, to disperse from a site on the south coast of England. The clam is farmed in Poole Harbour but has become established in Southampton Water. The modelling demonstrated the existence of a mechanism linking the clams found in Southampton Water to the farmed source in Poole Harbour.

Spreading beyond expected boundaries

The manila clam was introduced to Poole Harbour to create a fishery for this commercially important foreign shellfish. The clams are seeded and grown to a juvenile state on land before being placed within the fishery’s boundaries to complete their growth prior to harvesting. This method was employed to prevent spawning of the clam within the harbour and thus the potential spread of the species outside of the designated fishery. However, beds of manila clam have appeared all around the harbour, including low salinity areas which were previously thought to be lethal to the clam, and also in Southampton Water. HR Wallingford modelled the movement of the clam larvae to investigate whether the larvae could travel to Southampton Water and also how the larvae could survive in lower salinities than it was previously thought they could tolerate.

Identifying invasion routes

Larvae behaviour studies carried out at Bournemouth University, part-funded by HR Wallingford, indicated that the larvae of the manila clam are able to swim vertically through the water column and that they do so in conjunction with the state of the tide i.e. as the tide comes in they swim up, and as it goes out they swim down. This behaviour allowed them to move through the harbour (rather than stay where placed as was previously believed). We combined our existing hydrodynamic model of Poole Harbour with an ecological model of larval movement to consider whether this new mechanism would result in dispersion of the larvae to Southampton Water. Particles were added to the model and coded with the behavioural characteristics of the clam larvae. The model indicated that the larvae were able to move out of the mouth of Poole Harbour into open water and, once out of the harbour, the prevailing currents and tides eventually swept the larvae to Southampton Water.

Surviving in unsuitable environments

The second question, of how the clam was able to colonise low salinity areas which were believed to be unsuitable for it, was also answered through a combination of research at Bournemouth University and the use of HR Wallingford’s hydrodynamic model. Genetic work showed that the larvae developed with a preference for water of either 17 or 21 salinity and that they would actively move towards the preferred salinity as well as vertically within the water column. The ecological model showing the larval movement indicated areas of Poole Harbour where colonies of the clam should be found. On comparison with local records these model predictions were found to be accurate. This work has improved our understanding of how an invasive species can spread in UK waters.

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This work has improved our understanding of how an invasive species can spread in UK waters.

This work has improved our understanding of how an invasive species can spread in UK waters.

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Tom Matthewson

Tom Matthewson

Technical Director, Marine

+44 (0)1491 822474

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