The ecosystem traits index is proposed as a composite index of ecosystem robustness for use in marine resource management

Abstract

Abstract Ecosystem structure and function are seldom represented in ecological indicators used for resource management and conservation, despite their central position in stated objectives of international agreements and national policy on maintaining and conserving global ecosystems. Network theory provides capacity to change this situation. Inspired by the use of composite indicators in emergency warning, planning systems and in network analyses in many other applications, we show that a small suite of network-based indicators can provide a practical basis for measuring ecosystem structure in fisheries management. We suggest an Ecosystem Traits Index (ETI) that provides a rating of the combined ecosystem state and structural integrity. This index combines information captured by: the Hub index, which identifies species critical to system function; Gao’s resilience score, which provides a measure of system resilience due to the density of connections and flow patterns in the ecosystem’s food web; and the “Green Band” index (which measures pressure on ecosystem structure due to the mortality from human activities such as harvesting). Applying these indices to marine ecosystems of very different types showed that the combination of indicators is informative in each case and that each ecosystem’s unique state results from fishing pressure, environmental change, and inherent ecosystem structural robustness. Simulation-based tests demonstrated the indicators rapidly respond to, and consistently reflect, ecosystem state changes across marine ecosystem types, though they cannot distinguish the effects of individual stressors such as fishing mortality, habitat modification, climate or other environmental changes. We have focused on fisheries because fishery indicators should, in principle, have utility across any form of marine ecosystem pressure.