Marine Net Gain: An Overview

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What is Marine Net Gain?

Biodiversity net gain (BNG) aims to leave the environment in a better condition than previously and compares habitat losses and gains.

In 2018, following consultation, it was decided BNG would be mandatory for new terrestrial developments. For further details on BNG, please see our other article here. Consultation responses suggested extending BNG to marine developments to encourage sustainable growth and recovery of marine industries, and help meet net zero targets.

Marine net gain (MNG) will only be applicable to developments below the Low Water Mark, and is intended to cover most new marine developments in English waters. Each development would need to produce a level of gain proportionate to the losses related to it. MNG would not supersede existing environmental requirements, but would be a new requirement that developers will need to adhere to.


Public consultation on the principles of MNG took place for 14 weeks starting in June 2022. Consultees were asked to answer questions relating to nine different principles, all associated with the concept of MNG. During the consultation period, 92 responses were received, a summary of which are below.

Summary of Consultation Responses

Taking into account the fact that the marine environment is highly mobile, unlike terrestrial environments, it was largely agreed that MNG needs to use a whole ecosystem strategy to adequately positively impact both habitats and species.
When addressing the wider environmental benefits that should be included in MNG assessments, respondents suggested that the following should be included:

  • Sustainable fishing practices, such as the impact on commercial fishing, and fish recovery areas;
  • Climate change control practices, such as blue carbon habitats, and flood and climate control; and
  • Habitat benefits, such as creation and restoration of habitats.

In relation to whether or not MNG should  be mandatory for new developments in the marine environment, the majority of respondents agreed that it should be. Respondents also suggested various activities for which MNG should not apply. Potential exemptions included the following: 

  • Operational and maintenance activities;
  • Dredging;
  • Scientific research activities; and
  • Activities for meeting statutory functions. 

Most respondents agreed that both site-level and strategic interventions are important to ensure MNG is most beneficial to the marine environment. Some respondents highlighted that a more strategic approach would benefit smaller developments to avoid ‘piecemeal interventions’, while other respondents suggested that site-based interventions were particularly important to provide meaningful benefit to the local area impacted by the development.

Above is just a brief summary of the consultation responses. If you would like to read DEFRA’s full summary of responses to each consultation question, they can be found here.

You can find the MNG consultation documents here.

Ashfords regularly advises on environmental matters in the context of the marine environment. If you have any queries or would like further information on marine BNG, please contact our Marine team.

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