Methods development for cost-effective marine environmental monitoring at offshore wind farms in Norwegian waters

Current understanding of the environmental impact from offshore wind farms and experiences in monitoring practices, are restricted to soft-bottom habitats. Due to the large expansion of this source of energy, and the national and international drive to place large parks offshore, there is at present a strong need to further increase our knowledge of the impact on the marine environment in a wider range of habitats. At a national level, it is of importance to develop monitoring methods that are suitable for Norwegian sites and that are adjusted to impact levels expected from wind parks. Biological data on the impact of offshore wind farms in marine ecosystems are predominantly focused on the southern Baltic and southern North Sea. It is shown that large wind farms do have an impact on the marine ecosystem. The most studied effects relate to the introduction of hard substrate (the turbine foundation and scour protection) in an area made exclusively of soft sediments. This leads to an introduction of a new category of fauna, a higher productivity and a shift in community structure and species composition. In addition, the construction of an offshore wind farm excludes other activities with potentially high negative impacts on the marine ecosystem such as bottom trawling. These findings are not necessary applicable to rocky shorelines such as those bordering the Norwegian coast and the first full-scale offshore wind farm, Havsul 1. The Havsul site borders an open ocean with high average yearly wind speeds of more than 20 knots. A relatively nar-row shelf and steep underwater topography creates waves of substantial heights and a benthic marine ecosystem that is fundamentally different from the shallow water, soft sediment substrates in the southern Baltic and North Seas. Instead, areas in Norway with water depths suitable for today‟s design of offshore wind farms (down to a depth of about 30-50 m) have a complex topography and a mosaic of substrate types are present (rocky seabed, sand, gravel and stones) and are often exposed to severe waves and strong tidal currents. Keystone or-ganisms at an exposed and complex hard bottom environment can potentially include large kelp species (Laminaria), red algae growing on bare rock (e.g. Lithothamnion) and reef or bed forming species such as the horse mussel (Modiolus modiolus) and maerl (coralline algae). These structure-forming organisms support a high diversity of marine life and provide important ecosystem services such as feeding grounds for commercially valuable fish and crayfish species. No studies have so far investigated the effects from large scale offshore wind farms in this type of environment. The first year of benthic marine baseline data collection in the Havsul area, suggested that there is a lack of standards for monitoring methods at complex marine habitats dominated by bare rock, and kelp communities. We have applied a suite of methods chosen to detect changes in a range of habitats and trophic levels including tradi-tional sediment coring, metagenomic diversity estimates, video data collection and assessment of the kelp community. Preliminary results suggest that it is necessary to adjust monitoring practises to the local environment. This makes comparisons with other regions difficult and may jeopardise efforts to conduct studies of potential cumulative impacts. Benthic community structure assessments and large scale habitat mapping based on video mosaic data is particularly promising both in terms of cost effective collection of data, data quality and sensitivity.