Chapter 7: General discussion and conclusion
7.5 Limitation of the study and recommendation for future works
The use of indices that quantify the status of macrofaunal community in terms of structural and functional features provide a better step in achieving improved understanding of changes in ecosystem function following disturbance by aggregate dredging. The long term sampling regime applied in this study might also be useful in understanding the variation of ecosystem dynamics which is an important consideration when determining recovery status. There are, however, several limitation identified in this study. Firstly, the unavailability data in 2005 and 2006 created a gap in terms of following successional changes, particularly at the low intensity site. The second limitation was the lack of other physical data (acoustic and seabed imaging) which made the attempt to relate the macrofaunal community with specific sediment particles fairly difficult. In addition, one might argue the use of too many indices might add the complexity to the judgement. However, it was the aim of this study to make a comprehensive assessment using different indices with different characteristics. This difference was also the reason why the present study did not
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attempt to combine multiple indices (i.e. multi-metric analysis) for an easier interpretation
Based on the limitations discussed, it is recommended that the future works concerning system recovery should be carried out for a longer time series as well as with multiple physical parameters (e.g. seabed topography, hydrodynamic, organic contents) to support the biological data. However, it is acknowledged that this depends on the financial status of the project. It is also suggested that, for future works, some functional indices (e.g. BTA, FD and Rao’s) can be further analysed. Chapter 6 in the present study describes an initial attempt for a more detailed assessment based on multiple traits. A similar approach based on the traits in BTA, FD and Rao’s Q would be an interesting appraoch in understanding species characteristics and interactions that are the central factors of recovery.
7.6 Conclusion
Studies on the impact of human induced activities on ecosystems have been carried out extensively and will need to continue as such activities are increasingly vital for socio-economic gain. Different studies reported different levels of impact on ecosystem and this could be due to both intrinsic and extrinsic factors. Studies carried out in different areas suggest different responses of benthic fauna on habitat disturbance. This thesis provides a site-specific insight to the impact of physical disturbance on benthic ecosystem function through dredging activity. The use of various measurements does not simply complicate the interpretation of environmental status. Instead, multiple indices are useful indicators to assess the ecosystem based on different perspectives and purposes. The thesis also provides evidence that higher levels of physical disturbance impose greater damage to the ecosystem. The discrepancy of the findings at the high dredging intensity site in the present study with the prediction of recovery in previous studies by Boyd et al. (2004) and Cooper et al. (2005) demonstrate the importance of monitoring the impact for a longer period. This information is valuable as a reference for the environmental managers and policy makers when it comes to making decisions with regard to activities that damaging benthic habitat.
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