Abstract
The goal of this report is to assess the benthic development of the soft bottom faunal community in and around the offshore Prinses Amalia Wind Park (PAWP) near the Dutch coastal zone. The current report focuses on the development of soft bottom fauna, 10 years after the putting into use of the PAWP, and therewith 10 years of exclusion of fisheries in the wind park area. Comparisons were made between locations inside the wind park (QT) and reference locations outside the wind park (QAW). This analysis was done on available data from the baseline study in 2003, the T5 (2012), T6 (2013) and T10 monitoring in 2017. Trends in faunal communities were analysed, as well as effects of environmental conditions (i.e. sediment characteristics, fishing intensity) on the benthic fauna. Variables like number of species, abundance and several diversity indices were statistically analysed with univariate methods. Differences in community composition were analysed with multivariate methods. Moreover, possible correlations of several abiotic variables with benthos were investigated, which was not done in earlier research.
Overall, clear temporal effects on the species composition of the Prinses Amalia Wind park were present, both on the univariate data (i.e. number of species, abundance and diversity indices) and on the multivariate data (community composition). The species composition changed over time when comparing the survey sites over the different years. Of the tested variables, sampling year had the highest significance in comparison to the other environmental factors. This suggests that there is a strong temporal effect on the species composition in the data. Of the environmental variables that were analysed with multivariate statistics and multiple regressions, depth had a correlation with the species composition of the benthic community. Organic matter content and the D50 fraction of the sediment played a role in the diversity of the samples (Margalef-, Shannon Wiener- and Simpson index; except Pilou evenness). Fishing intensity does not seem to play a large a role in the composition of the benthic community. When 2003 is left out of the analysis, fishing has no effect, even when fishing intensity differs within and outside the wind park, especially in 2017. Furthermore, there is still a difference in community composition between the sampling years of 2012, 2013 and 2017, which cannot be attributed to fishing intensity. The low explaining power of the multiple regressions, as well as the multivariate analyses, indicated that temporal effects were overriding effects of environmental variables, and that other non-measured variables may be important.
Overall, 2017 seems to be a peculiar year, with large differences from previous years, with high abundances and low number of species and diversity indices. It is therefore advised to do another sampling campaign, since 10 years might not be enough to capture recovery of the species community after exclusion of fisheries. Analysis of additional environmental variables should be considered, such as additional sediment characteristics and bed shear stress. Additionally, different types of analyses on the data are advised, such as a trait analysis, a meta-analysis including other similar projects and the utilization of the BISI index. These might give more insight in mechanisms behind recovery after disturbance in different habitat types and help in management of nature conservation goals.