Abstract
This report evaluates a test of the Marine Growth Sampling Tool (MGST), a remotely operated vehicle (ROV)-mounted system developed to collect biofouling samples from offshore energy structures. The MGST was designed as an alternative to diver-based sampling, which has become increasingly impractical in Dutch offshore wind farms (OWFs) due to stricter safety regulations and higher costs. Effective monitoring of biofouling communities on OWF turbine foundations is essential for understanding ecological impacts, such as changes in biofouling composition and nutrient cycling. The MGST was tested in November 2023 at the Hollandse Kust Zuid offshore wind farm, using the damaged E04 turbine foundation. The test aimed to assess the MGST’s operational performance, including depth limitations, coating damage to turbine foundations, and sample quality. The MGST, mounted on a Saab SeaEye Tiger ROV, scraped biofouling from turbine foundations at depths between 4.5 and 20 meters. Three scraper types (metal, green plastic, and blue plastic) were tested. Over two days, the MGST successfully collected 21 biofouling samples. The tool demonstrated high precision, with only a 1% average deviation between programmed and actual sampled areas. There were no significant differences in sample quality, species richness, or abundance among the three tested scraper types, though the plastic scrapers wore down more quickly than the metal scraper. The test also evaluated the potential damage to the turbine foundation’s protective coating by quantification of particles present in the biofouling samples. Noting that all samples were collected in an MGST net with a mesh size 0.5 mm, in half of the samples no coating particles were found, and in the remainder the maximum total size of coating particles found in a sample was small, at 0.005% of the sampled area. No coating damage was observed on video. This indicates that the MGST causes negligible harm to turbine coatings, making it suitable for upscaling in long-term monitoring applications. Taxonomic analysis revealed a diverse range of species dominated by amphipods and anemones, and the sample quality was found to be high, like that of diver-collected samples. A comparison with the international BISAR biofouling dataset confirmed that the MGST samples fell within expected ranges for species richness and abundance. Assessment of the impact of processing biofouling samples to higher taxonomic levels to reduce costs, showed that geographic patterns in the BISAR data which were visible at species level, became invisible already at genus level. It is recommended to process samples at the lowest possible taxonomic level possible, ideally on species level. This will increase the reusability of the biofouling data for scientific studies and to answer questions that currently have not been asked yet. We conclude that the MGST is a viable alternative to diver-based sampling, offering a safer method for monitoring biofouling communities in OWFs. Further tests are needed to evaluate the efficiency of sampling harder structures, such as mussels, as well as thicker biofouling layers. Future comparative studies between MGST and diver-collected samples are also suggested to validate the tool’s broader applicability.