Power generated from marine energy devices, including those that harvest power from the waves and tides, has the potential to help meet the low-carbon energy needs of many coastal nations. However, these devices, and their related mooring lines, anchoring and buoyancy systems, and power export cables are still under development, resulting in a lack of understanding of potential environmental effects of these technologies. Locations suitable for marine energy development typically consist of rough waters, strong tidal currents, large waves, and inhospitable conditions for oceanographic measurements. Coupled with novel interactions between marine animals (particularly marine mammals and fish) and marine energy devices, these high-energy environments create a challenge for accurately observing, measuring, and analyzing environmental effects. Under the auspices of the International Ocean Energy Systems (OES), a collaborative project (Annex IV) was devised to identify and facilitate sharing of existing information on potential effects of tidal turbines and wave energy converters, and to inform permitting (consenting) processes that will enable deployment of these devices. In this paper, we explore the application of a variety of scientific fields to the examination of the environmental impacts of marine renewable energy devices, through three focused analyses. These analyses were conducted as part of the Annex IV initiative and are explored in greater length in the final report for the Annex IV effort; they focus on high-priority areas of concern for marine energy development that have appeared across several nations: 1) the interaction of marine animals with turbine blades; 2) effects of underwater sound from marine energy devices on marine animals; and 3) effects on the physical systems due to energy removal and flow changes from the operation of marine energy devices. These analyses synthesize the current state of scientific understanding, informed by field monitoring, laboratory studies, and modeling efforts, and identify key data gaps that limit the information regulators and researchers can apply to future device deployments.