Open ocean ecosystems, habitats and biodiversity are all properties of the ecosystem state (shown in the Conceptual Framework as Box 3) which is central to the assessment. Using the conceptual framework as a guide, human well-being is in part linked to sustained ecosystem services, which are in turn driven by the ecosystem state. Ideally a monitoring system feeding policy and governance would monitor the ecosystem state.

Ecosystem state changes include changes in primary productivity (which can be modelled based on chlorophyll data), the base of marine food webs, due to changes in ocean temperature, stratification and its interaction with the seasonal cycle, nutrients, and pollution from land-based nutrient input. These result in changes one step up in the trophic chain in zooplankton, and have repercussions further up in the ocean food web. These changes will have impacts on the rest of the pelagic ecosystem including commercially valuable species that are fished with consequences for people.

The remoteness and vastness of the oceans pose a serious barrier to a comprehensive open ocean ecosystem state monitoring system; it is simply impractical at present. Given scientific knowledge, educated guesses can be made about how ecosystem state, including biodiversity, is linked to stresses from human activities. In many cases these stresses are easier to measure comprehensively, at least for the few stressors that are thought to have global impact.

Ocean ecosystem features that are particularly vulnerable were assessed too, as a complement to a mapping of where the stresses are strongest. The potential wide-ranging impacts of acidification on calcium carbonate species (eg. Pteropods) and ecosystems (e.g coral reefs) were selected for this reason. The results not only show current and projected future state responses to acidification; they also serve as an indication of potential impacts on the wider global marine ecosystem, services and subsequently human wellbeing. This provides guidance for improved monitoring at strategic locations in the open ocean where vulnerability and stress are highest, to ensure that these features are protected and can continue to provide ecosystem services.

The economic consequences of a change in governance designed to change stakeholder behaviour driving an associated stress on the open ocean can be significant. It can therefore be useful to attempt to link ecosystem state through the services it provides to human well-being with an economic valuation of the ecosystem service being examined.

Key indicators/metrics were identified by the sub-theme underlined above, and shown in the following web pages.