Decommissioning – Relative Effects of Alternative Management Strategies (DREAMS)

Weighing up the pros and cons of different decommissioning options – studying how marine structures and decommissioning strategies affect ecosystems and the services they provide.

Objectives

Using systematic reviews, meta-analysis and advanced ecosystem models, this project aimed to:

• Assess the clusters and gaps in scientific understanding of structures on marine ecosystems
• Understand the linkages between ecological effects of offshore wind farms and provision of ecosystem services
• Statistically assess the global effects of structures
• Evaluate the relative effects of different Man-Made Structures (MMS) on whole-system marine productivity and biogeochemistry
• Uderstand the connectivity potential of structures in the North Sea

Mapping marine connectivity: hotspots in the North Sea

DREAMS created a Connectivity Importance Index (see image) using advanced modelling techniques—like hydrodynamic, biogeochemical, particle tracking, and network analysis—to show where marine structures are most connected. The strongest connectivity was found at 55°N, 4°E (see red squares), highlighting the Southern North Sea as a key area. Another important spot was identified at 59°N, 4°E (see darkest red square) in the Northern North Sea.

Image Credit: Plymouth Marine Laboratory and University of Plymouth.

The results are intended to guide decisions on where to install or remove marine structures. The findings are consistent with previous studies and emphasise key differences between oil and gas platforms and offshore wind farms in terms of their effects on productivity and nutrients. Oil and gas structures tend to have less impact, whereas offshore wind farms—because of their greater density—can significantly influence productivity and nutrient dynamics in and around their locations.

Diving into the data

DREAMS analysed over 530 data points from 109 studies to assess the potential effects of decommissioning marine structures. They found that MMS can support more ecological function than soft seabeds, but not more than natural rocky reefs. Different types of structures also have different ecological impacts.

There’s still not enough evidence to say whether decommissioning oil and gas or wind structures as artificial reefs is clearly beneficial. However, some data suggest that fully removing structures can harm ecosystem services, while leaving them in place or partially removing them may offer more ecological benefits.

Unfinished dreams – key evidence gaps remain

DREAMS found a major lack of real-world case studies on the ecological effects of different decommissioning options, making it hard for decision-makers to assess impacts or push for policy changes. While the project gathered a lot of evidence on how marine structures affect fish, invertebrates, and artificial reefs, big knowledge gaps remain—especially around newer structures like marine renewables. Key areas with missing data include hydrography, sediment processes, nutrient cycling, and impacts on algae, plants, and mammals. The team identified over 197 evidence gaps related to ecosystem services, mostly linked to wind turbines. Despite progress, much is still unknown about how MMS affect ecosystem services.