This thesis address ecological risks associated with the possible growth of marine renewable energy. Tidal power, wave power, ocean thermal energy conversion (OTEC) and currently expanding offshore wind power are likely to become common components of future seascapes. The world ocean is strongly affected by other marine activities and it is essential that the possible expansion of marine renewables takes place without causing further detriment to the ecosystem. Identifying possible ecological risks at an early stage of technical development facilitates adaptation and supports apposite regulation.
The five studies of this thesis address: (I) stressors from marine renewables in comparison with other human activities that can cause cumulative effects to marine ecosystems; (II) ecological risks of an offshore wind power project in Kattegat; (III) effects of a small tidal turbine on fish movements; and (IV-V) modeling of collision risks of large tidal turbines. Methodological contributions include procedures for handling assessment uncertainties, introduction of fish behavior in collision risk modeling, and stereo-video based in situ measurements of current speed and fish swimming speed.
The results indicate that marine renewables are associated with comparatively many different stressors with potential effects on marine ecosystems. The stressors from offshore wind power, wave power and tidal turbines are quite similar. Most stressors from marine renewables are already common as a cause of existing human activities; however, some are different and may have unprecedented effects. Particular uncertainties regard the ecological effects of OTEC. It was further shown that ecological risks from offshore wind power on cod can be effectively reduced by planning harmful installation procedures so as not to coincide with biologically sensitive periods and that risks for cod are insignificant during the wind power operation phase. For tidal turbines particular uncertainty regards underwater collisions. Here it was found that small turbines are unlikely to pose significant risk to fish. For large turbines the findings indicate that small fish are unlikely to be harmed while large animals may be at risk for collision under poor visibility conditions, such as at night.
Apparent ecological risks of marine renewables vary among the many technical designs and are not known to detail. Positive effects are possible and have not been studied here. By further reducing uncertainties and mitigating risks through technical adaptation, regulation and planning negative effects of expanding marine renewables can be alleviated. This thesis provides some recommendations for research, development and management.