'Scaling up' our understanding of environmental effects of marine renewable energy development from single devices to large-scale commercial arrays.

Global expansion of marine renewable energy (MRE) technologies is needed to help address the impacts of climate change, to ensure a sustainable transition from carbon-based energy sources, and to meet national energy security needs using locally-generated electricity. However, the MRE sector has yet to realize its full potential due to the limited scale of device deployments (i.e., single devices or small demonstration-scale arrays), and is hampered by various factors including uncertainty about environmental effects and how the magnitude of these effects scale with an increasing number of devices. This paper seeks to expand our understanding of the environmental effects of MRE arrays using existing frameworks and through the adaptation and application of cumulative environmental effects terminology to key stressor-receptor interactions. This approach facilitates the development of generalized concepts for the scaling of environmental effects for key stressor-receptor interactions, identifying high priority risks and revealing knowledge gaps that require investigation to aid expansion of the MRE sector. Results suggest that effects of collision risk for an array may be additive, antagonistic, or synergistic, but are likely dependent on array location and configuration. Effects of underwater noise are likely additive as additional devices are deployed in an array, while the effects of electromagnetic fields may be dominant, additive, or antagonistic. Changes to benthic habitats are likely additive, but may be dependent on array configuration and could be antagonistic or synergistic at the ecosystem scale. Effects of displacement, entanglement, and changes to oceanographic systems for arrays are less certain because little information is available about effects at the current scale of MRE development.