Abstract
1. Tidal energy is a dependable and clean power source that stands as a compelling alternative to fossil fuels. Despite this promise, tidal energy projects face barriers to practical implementation, and objections to proposed schemes often stem from perceptions of adverse ecological effects.
2. Early concerns surrounding the ecological effects of tidal range energy infrastructure arose largely from the construction stages of barrages rather than from later, longer term operational stages. Though research on this was under-planned, there is now a literature base. We synthesise the available current evidence of effects that both long-established range and novel stream technologies have on marine environments through systematic and exploratory literature approaches.
3. Fifty-four articles have been included in this review and produce a nuanced picture accompanying a steep learning curve in both tidal power system construction and operation.
4. Few of the widespread concerns are substantiated by evidence or in long-term monitoring of existing projects. There is evidence of alterations in hydrodynamics and sediment flux at tidal range power plants, as well as some animal behavioural changes around tidal stream turbines, though many apprehensions either remain unsubstantiated or result in neutral effects on marine ecosystems. Several positive ecological effects are identified such as greater productivity and species diversity within tidal range basins, as well as enhanced seabird foraging hotspots surrounding tidal stream turbines. Maintaining a tidal regime as close as possible to its prior state appears key to minimising adverse ecological effects and has been a major learning point for tidal range
5. Practical implication. This work provides foundations for environmental impact assessments of future tidal projects and may enable more informed choices and facilitate a priori mitigation planning.