Offshore wind energy is in its early stages in the United States, and consequently, there are few empirical studies to inform the potential for any environmental impacts. Europe, in particular, has established large offshore wind farms, which have been studied extensively. In those European studies, offshore wind farms have been shown to alter local marine environments, especially by introducing hard substrates that promote colonization and accumulation of biogenic debris from various marine organisms. Most of those effects were found to be localized and proximal to the wind turbine structures themselves. Until very recently, the Block Island Wind Farm (BIWF), with its five relatively small turbine structures, was one of the only opportunities for examining the conformance of European findings in US waters and beginning to understand any potential ecological changes triggered by the ongoing expansion of the US offshore wind industry.

In 2020, CSA Ocean Sciences Inc. (CSA) was contracted by the Bureau of Ocean Energy Management’s (BOEM) Opportunity for Real-time Development Environmental Observations (RODEO) program to conduct the fourth and final year of an ongoing study of the ecological impacts associated with the operation of BIWF. These studies focused on benthic and epifaunal communities surrounding three of the five wind turbines. The study’s design was informed by both previous studies at the BIWF but was revised to better understand any existence of changes in the benthic communities surrounding the structures.

The research and subsequent scientific paper, "Effects of the Block Island Wind Farm on Benthic and Epifaunal Communities" were published in the Journal of Coastal Research in November 2024 with study co-authors McMahon A., Erickson R., Tiggelaaar J., and Graham B. The primary goals of the study were twofold: one, to detect, measure, and monitor alterations to seafloor sediment composition, faunal abundance, diversity, and community structure at varying distances from the turbines and to determine the spatial and temporal extent of these effects and, two, to also monitor the faunal communities on the turbine structures themselves for changes in abundance and composition both among turbines and over time.

In-the-Field Ops

Sampling occurred at three turbines (T1, T3, T5) and in three control areas located over 250 meters from the turbines. Five distance-based strata were established around each turbine: foundation footprint, very near field (<30 m), near field (30–49 m), intermediate field (50–69 m), and far-field (70–90 m). Benthic infauna and sediments were collected using vessel- and diver-based grab samplers. Epifauna on the turbine structures themselves were collected as scrape samples, and divers collected video transects along the vertical extent of the turbine legs. Sediments were analyzed for particle size, total organic matter (TOM), and total organic carbon (TOC). Benthic infauna and epifauna species were identified to the lowest practical taxonomic level, and community metrics (diversity, richness, evenness) were calculated.

Investigation Findings

As seen in some European studies, the most notable changes in sediment particle size occurred in the immediate footprint of turbine foundations. Sediments surrounding turbine T1 (in deeper water) had the highest gravel content, while T3 and T5 were sand dominated. With increasing distance from turbines, gravel content generally decreased, and sand content increased, but these trends did not extend beyond approximately 90 meters from the turbines. TOM and TOC levels were generally similar between turbine and control areas, with minor, statistically significant differences in some strata. Importantly, no consistent evidence was found for progressive organic enrichment of sediments with distance away from the turbines, aside from accumulations of biofouling sloughing at the base of foundations.

Block Island Wind Farm study map. (Image credit: CSA)

Across all faunal samples taken, 28,025 individuals from 216 taxa were identified, of which Annelida (segmented worms) dominated at 84%, followed by Arthropoda at 8%, and Mollusca at 7%. The invasive carpet tunicate (Didemnum vexillum) was not present in Year 4, although its presence was noted in the Year 3 report. Moderate species diversity and evenness were observed across all turbines and strata. Integrating findings from previous studies to complete the picture for the four-year program, it was found that the number of unique infauna taxa increased by about 28%, suggesting either natural variability or potential long-term enrichment. Significant changes in faunal composition and abundance were also generally restricted to the immediate vicinity of turbine foundations. No evidence was found for a progressive, distance-dependent effect radiating outward from turbines.

Image from video transects showing varying epifauna growth among turbine structures. (Image credit: CSA)

Image from video transects showing varying epifauna growth among turbine structures. (Image credit: CSA)

The BIWF turbines caused measurable changes in sediment composition and faunal communities, but these effects were highly localized—primarily within the immediate foundation footprint and not extending far into the surrounding seabed. Both benthic and epifaunal communities exhibited high temporal and spatial variability, with no evidence of stable, climax communities forming on or around turbine structures. This dynamic nature is perhaps driven by natural fluctuations, hydrodynamic forces, and short life spans of dominant taxa. The turbines provided habitat for structure-oriented species, including mussels and fish, like the artificial reef effect recorded in European offshore wind farms and other offshore energy structures.

The Block Island Wind Farm has induced clear, but highly localized, changes to seabed sediments and faunal composition at turbine foundations. Beyond these immediate areas, the physical and biological environment remains largely unchanged, with natural variability and disturbance appearing to dominate community dynamics. This four-year study highlights the need for robust, long-term monitoring strategies to distinguish turbine-induced effects from natural fluctuations, especially as offshore wind development expands in US waters. The highly experienced marine ecology scientists at CSA were pleased to have the opportunity to contribute to the continuation of building an objective basis of information to inform assessments of impacts and risks to the marine environment as the offshore energy framework evolves.

This feature appeared in environment coastal & offshore (eco) magazine’s 2025 summer edition Rethinking Offshore Operations, to read more access the magazine here.