European Member States have agreed via the Marine Strategy Framework Directive to work towards achieving Good Environmental Status, via the Water Framework Directive to aim for Good Ecological and Chemical Status, and via the Habitats Directive to aim for Favourable Conservation Status. These in turn help to fulfil national visions such as that from the UK whose marine management aims to achieve ‘clean, healthy, safe, productive and biologically diverse oceans and seas’1. Hence all of these status conditions mentioned by the Directives implicitly rely on an understanding of and the ability to quantify marine environmental health, to measure any departure from it. This then requires us to determine the effects of natural and anthropogenic marine hazards and vectors of change on that health2 and then bring in coordinated management responses3.
Tett et al.,4 defines good ecosystem health as: ‘the condition of a system that is self-maintaining, vigorous, resilient to externally imposed pressures, and able to sustain services to humans. It contains healthy organisms and populations, and adequate functional diversity and functional response diversity. All expected trophic levels are present and well interconnected, and there is good spatial connectivity amongst subsystems.’ Hence in the VECTORS project, we equate this condition with good status as mentioned above.
The overall marine state (Fig. 1), shows the ecosystem components (as the biota, their non-living environment, and trophic and biogeochemical fluxes) overlain by high-level ‘internal descriptors’ of system state: organisation and vigour which are responsible for the external property of resilience, which buffers ecosystem state and services against externally imposed (anthropogenic) pressures and other boundary fluxes, thus maintaining system integrity. Health describes the ability to maintain system integrity, which together with resilience is an emergent property of the whole marine system. Hence natural system should be considered together with the human system, giving the social-ecological system; management concern is then increased if the health of the natural system is compromised by the human system, uses and users. The health may be adversely affected by endogenic unmanaged pressures, those occurring within the marine area being managed, and exogenic unmanaged pressures, those operating from outside the area such as climate change5.
Figure 1. A systems conceptualization of ecosystem health4