Impact of Windfarm OWEZ on the Local Macrobenthos Community


Title: Impact of Windfarm OWEZ on the Local Macrobenthos Community
Publication Date:
January 01, 2006
Document Number: OWEZ_R_261_T1_20090305
Pages: 79

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Daan, R.; Mulder, M.; Bergman, M. (2006). Impact of Windfarm OWEZ on the Local Macrobenthos Community. Report by IMARES - Wageningen UR and Noordzeewind. pp 79.

In this report the results are presented of a study on possible short‐term effects of the construction of Offshore Windfarm Egmond aan Zee (OWEZ) on the composition of the local benthic fauna living in or on top of the sediment. The study is based on a benthic survey carried out in spring 2007, a few months after completion of the wind farm. During this survey the benthic fauna was sampled within the wind farm itself and in 6 reference areas lying north and south of it. Sampling took place mainly with a boxcorer, but there was also a limited programme with a Triple‐D dredge. The occurrence of possible effects was analyzed by comparing characteristics of the macrobenthos within the wind farm with those in the reference areas. A quantitative comparison of these characteristics with those observed during a baseline survey carried out 4 years before was hampered by a difference in sampling design and methodological differences.


The conclusions of this study can be summarized as follows:


  1. Based on the Bray‐Curtis index for percentage similarity there appeared to be great to very great similarity in the fauna composition of OWEZ and the majority of the reference areas.
  2. Overall fauna densities within OWEZ were well within the range of densities found in the reference areas. The same holds for overall biomass values.
  3. Diversity within OWEZ, expressed in terms of species richness, evenness and dominance, was well within the range of values observed in the reference areas. #The relative fauna abundance within OWEZ was statistically not different from that in the reference areas.
  4. Differences between the mean densities of individual species in OWEZ and in the reference areas were tested for statistical significance for 22 box core species. In 6 cases such a difference was significant, but the OWEZ area never showed a significant difference with more than one reference area. In other words, for all species tested the density found in OWEZ was within the range of densities of at least 5 of the 6 reference areas.
  5. Differences between the mean densities of individual species inside OWEZ and outside OWEZ were tested for statistical significance for 10 Triple‐D species. In none of these species the mean density in OWEZ was significantly different from that outside OWEZ
  6. There is not any indication, that OWEZ differed in some way from (the majority of) the reference areas, but that statistical analysis did not confirm a significant difference.
  7. There seems to be no short‐term effect of the construction of the wind farm on the local benthic fauna composition
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