To tackle the joint aspirations of expanding the offshore renewable energy sector and assisting marine nature recovery, the UK Government is currently developing a new policy titled “Marine Net Gain”. This policy will require developers to leave marine biodiversity in a measurably better state than they found it at the start of development, and is similar to the Biodiversity Net Gain policy, which was developed for terrestrial and intertidal environments.

Biodiversity Net Gain relies on a metric (The Biodiversity Metric 3.1, Natural England) to calculate the value of biodiversity attributable to a development in the form of habitats lost, degraded, added or improved through the development. Several challenges arise when applying this approach and the net gain concept to the marine environment, including but not limited to the scarcity of knowledge on the current condition of UK marine habitats, strategies to restore them, and mobile species whose response to developments may not be captured by habitat impacts alone. With Marine Net Gain policy currently in the early stages of development, solutions to these uncertainties are still emerging.

This report uses data from Walney Extension Offshore Wind Farm to generate three offshore wind farm “scenarios” which were tested against an experimental marine version of Natural England’s Biodiversity Metric, to highlight some of the advantages and challenges of using a metric to calculate biodiversity value of marine environments, as well as some of the more general challenges of implementing Marine Net Gain policy.