Surveys of Hard Bottom Communities on Foundations in Nysted Offshore Wind Farm and Schönheiders Pulle in 2004

Report

Title: Surveys of Hard Bottom Communities on Foundations in Nysted Offshore Wind Farm and Schönheiders Pulle in 2004
Authors: Birklund, J.
Publication Date:
May 01, 2005
Document Number: 52878
Pages: 46
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Citation

Birklund, J. (2005). Surveys of Hard Bottom Communities on Foundations in Nysted Offshore Wind Farm and Schönheiders Pulle in 2004. Report by Danish Hydraulic Institute (DHI) and ENERGI E2. pp 46.
Abstract: 

Deployment of foundations in Nysted Offshore Wind Farm started in the autumn of 2002 and the construction work including placement of stones in foundation chambers and around the foundations as scour protection ended in the spring of 2003. The first post-construction survey of the fouling community on shafts and stones was conducted in October 2003. An almost similar investigation was carried out one year later in October 2004 and supplemented with surveys at Schönheiders Pulle with the aim of providing data on a natural hard bottom community on a stone reef close to the wind farm. 

 

Common mussels and barnacles dominated the fouling community in the wind farm in 2004. The biomass of the community has increased significantly since 2003 due to a rapid growth of the mussels. However, the biomass on shafts and stones was still below the biomass at the monitoring mast deployed in 1997 and at Schönheiders Pulle. It is expected that the biomass on the shafts will approach the maximum level for mussel populations in the area during the next year. 

 

The structure of the fouling community was uniform around the foundations but changed with depth on both shafts and stones. The number and biomass of the dominantspecies of mussels, barnacles and the amphipod Gammarus sp. was lower in deeper water and other species of crustaceans increased with depth. These changes in community structure were attributed to depth-related hydrographic changes, affecting the flux and settling of larvae, availability of food and growth and stirring of sediment from the seabed.

 

The community of macroalgae was dominated by redalgae but the number of species was low. Macroalgae has disappeared from the shafts since 2003 and excluded by the rapid growth of the mussels with the exception of the transformer station, where algae were attached to patches with no or few mussels on the shafts. The community of macroalgae at Schönheiders Pulle was similar, irrespective of the depth and similar to the community on stones in the wind farm when assessment was based on biomass. The dominant species of redalgae were the same but the species composition was different in the two areas because the distribution of the less common species varied. Two less common species of redalgae recorded at Schönheiders Pulle were not found in the wind farm. The future development of the community of macroalgae in the wind farm is expected to depend on the growth of the mussel population and the space competition between algae and invertebrates.

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