There is an increasing awareness that knowledge of the functional diversity of a community is key to understand how the community responds to environmental and anthropogenic pressures. The Belgian Part of the North Sea (BPNS) represents a highly dynamic area that is subject to a variety of human activities. The main objective of this study is to investigate the usefulness of functional diversity indices and fuzzy correspondence analysis (FCA) to evaluate their applicability in assessing changes in benthic functional properties in the frame of environmental impact assessments (EIAs) for dredge disposal, sand extraction and offshore wind energy exploitation. Ten traits were selected, subdivided in 47 modalities, including both response- and effect traits. Functional diversity was quantified through different functional indices while shifts in trait composition due to anthropogenic pressure were determined by FCA. The analyses were based on a benthic dataset of 1262 samples.
Results revealed that under chronic pressure of high disposal or sand extraction, the functional diversity indices – especially functional richness - showed a clear response. However, considerable variation (decrease/increase) was found for the index values between the impacted sites. Within the offshore wind farms, findings for the functional diversity indices were less pronounced. The FCA graphs revealed a shift in trait composition in all cases except for Macoma balthica and Nephtys cirrosa habitat in the dredge disposal case.
The BPNS - with different types of pressure and levels of impact - provided the ideal platform to assess the potential of biological trait-based indicators. While responses are complex and dependent on several aspects such as local habitat, pressure type or level of impact, our results proved that functional trait analyses are a necessary and complementary tool in future environmental impact assessments.