Marine renewable energy projects (MREs) are supported by mandatory environmental monitoring programmes due to assumed environmental impacts. These programmes concentrate on the resultant effects of single industrial projects onto biological and physical components contributing to the local ecosystem structure. To date, impact assessments at the ecosystem functioning level (e.g. trophic interactions, nutrient cycling) are largely lacking. This critical knowledge gap hampers our ability to answering the “so what” question when assessing environmental impacts, i.e. whether the observed impacts are classified as good, bad or neutral, and/or acceptable or unacceptable. When assessing MREs, there is a fundamental need to focus on ecosystem functioning at relevant spatial and temporal scales to properly understand ecological impacts and its consequences. Here, we make a science-based plea for an increased investment in large scale impact assessment of MREs focused on ecosystem functioning. This presentation will cover a selection of examples from MRE monitoring programmes, where the current knowledge has limited conclusions on the “so what” question. Further, applications will demonstrate how a proposed ecosystem functioning approach at an appropriate spatial and temporal scale could advance our current assessment. These examples will illustrate the need to expand the current level of MRE monitoring beyond that of community structure and of individual industrial projects. This work will advance and strengthen collaborative MRE monitoring strategies, facilitating scientists, developers and regulators to answer the much needed “so what” question when undertaking environmental assessments, and reassuring stakeholders with high confidence over these assessments.