Report of the Regional Ecosystem Study Group for the North Sea (REGNS)

A meeting of the ICES Regional Ecosystem Group for the North Sea (REGNS) took place in May 2006 which continued the ambitious task of drawing together different types of data relating to pressure and state changes in the North Sea Ecosystem and to undertake an integrated assessment. The assessment has provided some valuable insights into the significance of the relationships between different pressure and state changes at different scales and the time scales over which changes take place. For example, plankton community data in relation to the physical and chemical oceanography reveals both gradients of response to the major riverine inputs of nutrients into the North Sea and sources of nutrients from the Atlantic. In addition, an assessment of all variables reveals two relatively stable states in the North Sea, one pre-1983 and the other post-1997. The intervening years are dominated by high ecosystem variability which represents a transition from one state to another and in part explains the number of studies which highlight different years for regime shifts. We conclude that defining such shifts is sensitive to the number and type of variables included in such analysis. Further evidence of a gradual regime shift in the ecosystem is presented for ICES

sub-region IVb2 a region subjected to relatively high human pressure, but here this shift appears to have occurred between 1991 and 1998. The sensitivity of such analysis to changes in temporal and spatial scales is explored as is the dependency on the number and type of ecosystem variables. By better understanding the relationship between the causes of change at different scales in time and space it should be possible to set more realistic targets for the management of human pressures.