Thresholds of ecological indicators are required to delineate ecosystem status. These thresholds represent points at which a small increase in one or many pressure variables results in an abrupt change of an ecosystem response. Developing such ecosystem thresholds needs to include both environmental and anthropogenic pressures. Here we develop thresholds using gradient forest and general additive model methods for a suite of ecological indicators in response to multiple pressures that convey ecosystem status for large marine ecosystems from the US Pacific, Atlantic, sub-Arctic and Gulf of Mexico coasts.
We found observations of thresholds in ecological indicators based on multiple pressures. Critical point analyses indicate that commercial fishing above approximately 2.5 t/km2and exploitation above 20-35% will result in a change in the direction of ecosystem structure and functioning, but that increases in environmental pressures can have both positive and negative effects. Our findings indicate that thresholds of ecological indicators are useful tools for comparing the impacts of environmental and anthropogenic pressures across multiple ecosystems and these critical points can be translated into Ecosystem-Based Fisheries Management decision criteria.