Evaluating marine ecosystem health: Case studies of indicators using direct observations and modelling methods

A major challenge in ocean and coastal management is to find simple ways to evaluate the health of such complex ecosystems. This task may prove complicated as selection criteria needs to be established for choosing appropriate indicators and evaluation tools which do not mask or leave out inherent ecosystem properties and dynamics. Here, we review some empirical analyses and modelling techniques which can be used to derive environmental health indicators. With a series of case studies ranging from the combined use of structural and functional attributes of the system, to modelling outputs that integrate the biological and physical environments, we illustrate the usefulness and complementarities of these methods to assess ecosystem health. The choice of relevant indicators will depend on the ecological questions raised as well as the biological and habitat components considered which can range from a single level (individual or population) to multiple levels (community or ecosystem-based indicators) in the ecosystem. Each method has its own capabilities and limitations that may render it useful or insufficient in some cases. We suggest, however, that, whenever possible, the combination of ecological attributes and tools should be used to improve our knowledge and assessment of marine ecosystems for better management and conservation in the future.