Muddy thinking:Ecosystem-based management of marine benthos

Globally, a number of states and parties are developing ecosystem-based approaches to environmental management. For the North Sea, the Convention for the Protection of the Marine Environment of the North-East Atlantic and North Sea Conference initiatives have identified a number of metrics for possible use in managing the benthos. We argue that the development of this framework needs to recognize that it is impacting activities which can be managed and that science should concentrate on the development of both robust decision support (performance) metrics and environmental state (descriptive) metrics in order to inform this management. A number of case studies are used to illustrate the strengths and failings of some of the proposed metrics. Performance metrics should be linked closely to the impacting activity. Thus, changes in the metric can immediately trigger a management response. We consider various proposed metrics and comment on their utility in the context of managing fisheries effects. Descriptive metrics, such as diversity indices, are useful for identifying patterns in community structure and assessing the potential consequences of impacts. However, they do not directly link changes to particular activities, making it difficult to assign causality and, therefore, apply management. To date, much of the focus of these considerations has been on taxonomic-based measures. We go on to consider the metrics that can also be developed to assess the functioning of the ecosystem. We conclude that, at present, there are few robust metrics to describe either the environmental state or the extent of fishing impacts for benthic systems. There is, therefore, an urgent need for scientific advances in this area