Early colonisation of a concrete offshore windmill foundation by marine biofouling on the Thornton Bank (southern North Sea)
Kerckhof, F.; Norro, A.; Jacques, Th.; Degraer, S. (2009). Early colonisation of a concrete offshore windmill foundation by marine biofouling on the Thornton Bank (southern North Sea), in: Degraer, S. et al. Offshore wind farms in the Belgian part of the North Sea: State of the art after two years of environmental monitoring. pp. 39-51 In: Degraer, S.; Brabant, R. (2009). Offshore wind farms in the Belgian part of the North Sea: State of the art after two years of environmental monitoring. Management Unit of the North Sea Mathematical Models, Marine Ecosystem Management Unit/Royal Belgian Institute of Natural Sciences: Brussel. 287 + annexes pp., more |
| Abstract | During late spring of 2008 the first 6 windmills of the C-Power windmill park were built on the Thorntonbank, some 30 km off the Belgian coast. Within the coming years, more windmills will be implanted in various windmill parks in a designated area of the Belgian part of the North Sea (BPNS). With the construction of windmills, a new habitat of artificial hard substrate is being introduced in a region mostly characterized by sandy sediments. This will increase the habitat heterogeneity of the region and the effect of the introduction of these hard substrates the so-called reef effect – is regarded as the most important change of the original marine environment caused by the construction of windmill farms. A monitoring programme was set up to sample the biofouling on the new hard substrates associated with the windmills. At the moment of sampling, only the sub- and intertidal parts of the turbine foundations, made of concrete, were available for colonisation as the scour protection was not yet fully deployed yet. Six semi-quantitative samples for epibiota were collected in the autumn of 2008. The subtidal samples were taken by scuba divers at four different depths all along the foundation of one of the windmills and a vertical video transect was made. Samples were taken by scraping the fouling organisms from a sampling surface area of 6.3 dm². The scraped material was collected in plastic bags that were sealed and transported to the laboratory for processing. After preservation of the sample, the organisms were indentified and an estimate of their density was made. After about 3½ months, the submersed part of the foundation was already totally and heavily colonised by epibionts and also the intertidal zone was almost completely covered. A clear depth zonation could be observed. A species list was compiled listing 49 species: 1 Protoctista, 4 algae and 44 invertebrates. The vegetation was restricted to the intertidal zone and rather sparsely developed. Only four species of mainly filamentous algae were present: Blidingia minima, Ulva intestinalis, U. Compressa and Bangia fuscopurpurea. A total of 44 invertebrate species was identified in the samples. However, only a few species were really abundant. The most numerous (> 1000 ind/m²) or abundant species were the giant midge Telmatogeton japonicus, the amphipod Jassa herdmani, the barnacle Balanus perforatus and the bryozoanElectra pilosa. All other species were far less abundant with the exception of Phtysica marina, the only caprellid present (100-1000 ind/m²). Taking into account the short (i.e. 4-6 months) period of time available for colonisation of the foundation, the number of 49 spp. is considered high compared to other hard substrata in the Belgian part of the North Sea (BPNS) and included several uncommon species for the Belgian fauna. Four non-indigenous species were found: the slipper limpet Crepidula fornicata, the New Zealand barnacle Elminius modestus, the giant barnacle Megabalanus coccopoma and the giant midge Telmatogeton japonicus. All four species, already known from the area, are opportunists and early colonisers after disturbance, taking advantage of man-made structures and disturbed conditions to settle. |
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