Development of indicators of ecosystem functioning in a temperate shelf sea: a combined fieldwork and modelling approach

A conceptual model of the main carbon and nitrogen flows through pelagic and benthic food webs was used to identify the key biogeochemical processes representing ecosystem functioning, and to select indicators of each of these processes. A combined fieldwork and modelling approach was used to provide the data required to evaluate the indicators in terms of their suitability for assessing and managing the impacts of climate change and demersal trawling. Four of our 16 proposed indicators (phytoplankton production and productivity, near-bed oxygen concentrations and oxygen penetration of the seabed) met the majority of criteria we used for evaluating indicators. Five indicators (depth of anoxic sediment, zoobenthos biomass, production, productivity and bioturbation potential) did not comply with sufficient criteria to be considered as good indicators. Six of our proposed indicators (zooplankton biomass, size structure, production and productivity; ecosystem productivity; ecosystem balance) could not be assessed for sensitivity and specificity using our models, and therefore need to be addressed in future work aimed at improving both the models and the fieldwork. Our results indicate that evaluation of indicators is difficult, because of the number and variety of human pressures which need to be considered in reality, and the interactions between these pressures and the ecosystem components which they affect. The challenge will be to establish if there are indeed any indicators which are able to meet the majority of criteria for good indicators in holistic ecosystem-based assessments.