The occurrence of regime shifts in large marine ecosystems is unproven and controversial. Despite this, a number of marine regime shifts are reported to have occurred during the last century. These shifts have been largely attributed to overfishing and climate change, and have had important consequences for marine ecosystem structure and function. Understanding the relationships between ecosystem pressures and responses is a critical step towards an effective ecosystem approach to management. Ecosystem models are a useful way of investigating how ecosystems respond to changes in pressures at the component and system level. This thesis aims to (i) define a set of quantitative thresholds for defining large-scale changes in marine ecosystem components in historical data and model simulations, (ii) characterise changes in the Irish Sea marine ecosystem that were observed between 1973 and 2002, and (iii) investigate whether 3 UK Ecosim models are capable of simulating the observed ecosystem level changes in response to trends in fishing and climate. System-level changes are measured using 12 model-based indicators of ecosystem state. Marine ecological regime shifts are defined as changes in marine community structure that occur over a 1-7 year period with an amplitude of at least 46% of the largest difference in indicator value. They persist on a decadal to multi-decadal scale and are associated with changes in biological communities spanning over at least 3 trophic levels. The criteria are used to diagnose an ecological regime shift in the Irish Sea in the late 1980s. Despite the inherent uncertainties associated with ecosystem models, all 3 models show that they are able to provide insights into the ecosystem responses to fishing and climate pressures, and that other factors are likely to have been important in explaining observed changes in the UK's marine ecosystem state. This suggests that they will be useful tools for "end-to-end" ecosystem analysis, which will be important in understanding the relationships between ecosystem pressures and responses.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:577148 |
| Date | January 2009 |
| Creators | Keeble, Kathryn |
| Publisher | University of Newcastle Upon Tyne |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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