Determining the 'health' of estuaries: Priorities for ecological research

'Ecosystem health' is a relatively new concept for environmental science and management. Although at least two international journals use the term in their titles, there have been few applications of it for estuaries and soft-sediment habitats around the world. In this paper I: (i) introduce the ideas behind ecosystem health, and assess their relation with other usage such as 'integrity' or 'quality'; (ii) sketch the sorts of multidisciplinary studies that could contribute to an assessment of health of an estuary and how these must be approached in developing useful indicators; and (iii) make a case for including measurements of the rates of ecological processes in such an assessment. These rate measurements, termed 'ecoassays', focus on important processes such as decomposition, recruitment, predator-prey interactions, and the like. A case study is introduced wherein these processes were assessed in mangrove stands of estuaries around Sydney, New South Wales, by explicitly comparing the rates of herbivory and decomposition of mangrove leaves, attack of fallen wood by shipworms, and colonization of pneumatophores by algae, as well as with more traditional estimates of 'standing stocks'. Not surprisingly, the different measures retrieved various patterns and the challenge now is to integrate these into a scheme that indicates something of value. The potential utility of such measures is discussed in relation to the various scientific and managerial requirements of environmental monitoring.