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Title: The distribution and potential northwards spread of the non-native gastropod Crepidula fornicata in Welsh coastal waters
Author: Bohn, Anne Katrin
Awarding Body: Prifysgol Bangor University
Current Institution: Bangor University
Date of Award: 2012
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Understanding the processes that determine the spread of non-native species (NNS) is critical if their impacts on native species biodiversity and ecosystem processes are to be mitigated. The secondary spread of NNS may be controlled by a variety of factors including their dispersal potential, the availability of suitable habitats, and their ability to cope with biotic and abiotic conditions in the novel environment This thesis investigates patterns of distribution and abundance of the non·native gastropod Crepidula fornicata in Welsh coastal waters. In a combination of field and laboratory observations of larval supply, larval settlement and post·settlement processes, combined with work on limiting factors such as low temperature, I investigated factors controlling its current adult distribution and potential for further northward colonisation from its current northernmost Welsh population, the Milford Haven Waterway (MHW). Results of this research project showed that C. fornicata is well established in the MHW, with locally superabundant aggregations and no indication for red uced reproductive success. It occurs across a variety of habitat types and the availability of certain hard substrata was fou nd to most likely even facilitate population establishment This indicates that limited habitat availability and decreased reproductive potential due to the exposure to sub-optimal seawater temperatures unlikely explain its absence from the coastal waters of Mid and North Wales. Benthic recruitment in the MHW, on the other hand, was generally low and occurred during a much shorter time period compared to the long larval season, indicating that settlement and post·settlement processes may be highly important in controlling adult distributional patterns. Early post-settlement mortality (EPSM) is likely important in determining patterns of adult distribution, whilst larval supply and associative larval settlement seem to be of minor importance. However, my results apply only to the distribution of adults in the intertidal, where exposure to harsher environmental conditions probably results in higher EPSM. Lastly, I found that the availability of certain microhabitats might attenuate the high levels of EPSM in the intertidal, thus having considerable impacts on fine-scale adult distributional patterns. The supply of late-stage larvae, in combination with hydrodynamic conditions and larval settlement behaviour, however, seems to be most important in limiting population spread at a regional scale, due to the likely presence of subtidal populations. This shows the importance of incorporating settlement and post-settlement processes into studies on recruitment success when aiming to predict the potential spread of a potentially harmful invader.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available