Abstract
This pre-survey report on biological fouling (NZW-MEP task 1.1.2) covers a description of the methodology, the results of the pre-survey into existing knowledge and approach of monitoring.
The goal of the monitoring is to investigate if biological fouling in the OWEZ windfarm has a different pattern, compared to what can be expected based on existing knowledge. The aim is to deliver information on the nature and thickness of the fouling on turbine support constructions, as a function of time. It holds the framing of an assessment of the (succession of) species composition and the expected biomass through the successive years. The monitoring details for the biological fouling monitoring will be attuned to the existing inspection procedures and with the inspection activities regarding the corrosion monitoring activities.
From literature an oversight is provided on the fouling that can be expected on man-made structures in the North Sea. Important aspects are among others geographical location, species composition, zonation and succession of the fouling community during successive years. The results provide a proper oversight of the fouling that can be expected on the monopiles of the Offshore Windfarm Egmond aan Zee (OWEZ). The type and extent of fouling is location specific. The extent of fouling (biomass) and species composition and succession is determined by influence of both abiotic and biotic parameters, i.e. temperature, turbidity, sand scour, larvae abundance, et cetera. Two studies in the Dutch coastal zone provide information on which an expectation for the fouling at the OWEZ can be based. These studies concern off shore NAM-platforms and artificial reefs.
The fouling community that might develop on the offshore structures of the OWEZ windfarm could be as follows: the first colonisers after installation are expected to be hydroids (within several weeks), followed by mussels, barnacles and anemones. Surface coverage of these species will increase during the first growth season (i.e. first year). More species will settle during time: mussels (Mytilus edulis and M. galloprovincialis), anemones Metridium senile, Obelia spp and Tubularia spp. Also a clear vertical zonation of the fouling species is expected. The first (upper) zone is expected to be fouled with hard fouling, probably dominated by a single species, likely by the mussel M. edulis. At lower zones soft fouling is dominant, existing in anemones and hydroids, although growth of soft fouling species might limited by any sand scour.
The yearly monitoring will show the exact fouling composition and succession.