The U.S. Environmental Protection Agency (EPA) defines ecological risk assessment as the process of evaluating “…the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors” (EPA, 1998).
The EPA identified multiple steps in performing an ecological risk assessment (EPA, 1998). The first step is problem formulation, which consists of systematically identifying potential stressors, exposure routes, and ecological effects. The critical step in problem formulation is the development of a conceptual model that diagrammatically identifies how a stressor may affect ecosystem receptors, as well as the appropriate risk assessment endpoints (measurable ecological variables) needed to test risk hypotheses about stressor and receptor interactions (EPA, 1998).
The EPA has identified several practical benefits from developing conceptual models, shown in Table 1. Aside from the utility of such models for clearly and visually communicating risk, the formation of a conceptual model allows one to understand linkages between biotic and abiotic variables within an ecosystem; develop risk hypotheses about which receptors are most likely to be adversely affected; and identify the data needed to characterize risk probability. In the case of a marine and hydrokinetic technology (MHK) device, an example of a risk hypothesis could be that noise from device operations (the stressor) could exceed the tolerance thresholds of demersal fish species (receptors), resulting in avoidance of the MHK device and a subsequent decrease in the abundance of affected species (assessment endpoint) in the vicinity of the device.