Emu Limited was commissioned by Kentish Flats Limited to undertake a marine ecological survey of two turbine foundations, within the Kentish Flats Offshore Wind Farm.
The aims of the study were to investigate the faunal colonisation of the subsea monopile foundations, using diver collected stills photography and video footage, MNCR Phase II recording data, and collection of scrape samples. The survey was undertaken approximately three years after installation of the turbine foundations.
The survey of turbines numbered D2 and C4 (see Figure 1) was undertaken on the 30th July 2008. The following data was collected at each of the 2 turbine monopiles;
- Stills photography of the monopiles from sea surface to seabed,
- Video footage from sea surface to the seabed,
- Video footage of the seabed within the immediate vicinity of the monopile,
- Four surface scrapes (0.01m2) on each monopile,
- MNCR Phase II biological recording.
The recorded species during the survey were comparable for the two turbines surveyed. The fauna recorded on the foundations of these two turbines are considered likely to be generally representative of the fauna colonising all of the foundations at the Kentish Flats offshore wind farm site, notwithstanding the potential for localised features / communities.
The predominant species found on the turbines were barnacles in the intertidal area, through to an infralittoral zone, which was dominated by the mussel Mytilus edulis, with the anemones Sagartia elegans and Metridium senile. Below the mussel zone, the area became dominated by anemones along with barnacles, hydroids and the tube forming worm, Pomatoceros sp. All of the recorded species are typical colonisers of hard substrates and are regularly found on man made surfaces in UK waters.
At the seabed, the shelly sand and gravel substrate was, in places, almost completely covered with the starfish Asterias rubens. This species is very common and could be expected to be present given the considerable density of its prey species, Mytilus edulis on the turbine foundations.
As a broad overview of the monopiles, three zones were present, which can be matched to biotopes described in Connor et al, (2004). The species assemblages recorded on the monopiles and their corresponding biotopes are:
- the upper barnacle dominated zone (LR.HLR.MusB),
- the infralittoral Mytilus edulis zone (IR.LIR.IFaVS),
- the Metridium senile fouling communities (CR.FCR.FouFa).
These biotopes are typical for this type of hard substrate, although the biotopes were relatively impoverished in some areas.
The biomass values for the scrapes taken at each biological zone on the monopile confirmed that Mytilus edulis is the major biomass contributor and accounts for the intra-zonal variability in biomass observed.