Since the notion of 'health’ was introduced to the field of ecosystem assessment in the late 1980s, ecosystem health has become a source of concern for scientists, environment managers and the public, and protecting this health is the new goal of ecosystem management. Ecosystem health is generally accepted in terms of 'system organization, resilience and vigor, as well as the absence of signs of ecosystem distresses', which also includes the presence of essential functions and key attributes that sustain the life of the system. A healthy ecosystem is defined as being 'stable and sustainable’; maintaining its organization and autonomy over time; and resilient to stress. Due to the complexity and diversity of ecosystems, various conceptual frameworks, methods and indicators have been put forth for assessing ecosystem status and environmental quality. Although more and more attention has been given to marine ecosystems of late, assessment studies of these systems are still in their infancy.
The rapid development of extensive mariculture in China is placing pressures on marine ecosystems, which in turn affects the health and sustainability of mariculture development. The mariculture ecosystem is a special and complex system, which is under intense pressure by human activities. The main features of this ecosystem are simple biological community structures, dysfunctional material and energy recycling, and an easily degradable system. The ecological problems in mariculture ecosystems include the deterioration of water and sediment environment, increased eutrophication, damage of natural biological communities, and decreased biodiversity. The degraded habitats will subsequently impact the development of mariculture by causing decreased seafood quality and frequent occurrence of diseases.
In China, health assessments of various natural coastal ecosystems have been attempted in recent years, such as the Yangtze River Estuary, Yellow River Estuary, Jiaozhou Bay and some coastal wetland ecosystems. However, there still remains no published study focusing on the health of mariculture ecosystems. To assess the pressure, state and responses of the ecosystems that support aquaculture, an integrated framework and method was developed in the present paper for assessing the health of mariculture ecosystems represented by those in embayments. The framework and method was developed through an analytic hierarchical process and included 25 indicators. The assessment approach followed the Pressure-State-Response (PSR) processes. The Pressure layer included two components: external pollution pressure (influx of nutrients, oil and heavy metals into the mariculture system) and aquaculture pressure (aquaculture density/scale, degree of self-pollution and cultured species diversity). The State layer included four components: hydrological condition (water exchange capacity), water quality (concentrations of nutrients, oil and heavy metals, dissolved oxygen level/COD, water transparency/SPM), sediment quality (content of organic carbon/nitrogen/phosphorus, concentration of oil and heavy metals, ORP) and biological community quality (biodiversity index of phytoplankton, zooplankton and benthos, abundance of microbe/fecal coliforms, and integrity of significant habitats). The Response layer included four components: HABs occurrence, aquaculture diseases, aquaculture product quality, invasion of alien species. This is the first attempt to establish an evaluation method concerned exclusively with marine aquaculture ecosystems in China. This method is expected to be a tool for ecosystem health assessment and adaptive marine management in mariculture domains.