The potential of offshore wind farms to spread marine alien species: A Norwegian case study and review of current evidence

Alien species are organisms that spread into new areas where they do not naturally occur, aided by human activities, and are often associated with artificial structures in inshore areas. Offshore wind farm (OWF) developments are occurring rapidly and represent an increasing surface area of artificial structures i.e. novel hard habitat that could aid the establishment and spread of alien species in areas otherwise lacking suitable intertidal and shallow subtidal habitat. 

There is concern that wind farm structures will act as stepping-stones or refuges for alien species. Indeed, in the southern North Sea, offshore energy structures already do act as habitats for alien species, and several other examples evidence this worldwide. Despite this, and national and international policy requesting improved knowledge on alien marine species, new introduction pathways and needs for an early-detection system, there remains no formal monitoring programme for alien marine species in Norway and their effects related to OWF remain unstudied. However, in the latest ocean management plans the government states that they want to increase the knowledge on and monitoring of alien species. Our report underlines an urgent need to initiate monitoring promptly to create a baseline for planned new ocean-based activities.

Here we theorise how OWFs may increase the spread to Norway through three mechanisms: 1) using OWFs as stepping-stones in dispersal, 2) direct transport to and from OWFs and 3) refuges from fishing. For each, we collate observations of relevant alien taxa and identify opportunities to close knowledge gaps to facilitate national and commercial obligations for biodiversity protection. We conclude that effective monitoring of OWF activities presents a useful opportunity to better understand the risk of spreading alien marine species in Norway and that structure cleaning practices can be designed and implemented to reduce this risk akin to those being developed for ship hulls.