Bfn Conclusions ecoblock revetments: verschil tussen versies

Versie van 24 okt 2017 om 12:02

There were large differences in the development of seaweed coverage in the first 1.5 years after laying the blocks. The development of Fucus vesiculosus was particularly fast on BfN-hydroblocks and Hillblocks. The fact that Fucus vesiculosus was developing faster on BfN-blocks as compared to standard hydroblocks can likely be explained by water retention by the blocks. Since all blocks were produced by the same standard procedure at the same factory, it is unlikely that there are differences between the blocks other than the pits. The coverage rate of gutweed remained remarkably high throughout the first year on hydroblocks with ecotop. There may have been a competition for space between the pioneer species of gutweed and the Fucus species. Gutweed are known as pioneering species that develop on bare substratum. Gutweed are strong interference competitors, but only under conditions that are stable, as they are relatively sensitive to grazing and desiccation (Hurd et al. 2014). The ecotop seemed to stimulate gutweed growth the most, possibly by their relatively high moisture retention capacity. This might have resulted in reduced space available for brown seaweeds to settle.

The presence of amphipods strongly correlated with Fucus biomass. These algae are an important food source for them. Crustaceans like these are in turn a food source to bird species like ruddy turnstones, which are known to use dykes as foraging habitat. The rapid colonization and biomass development on several of the block types tested may therefore benefit these species. Based on the experiment, it is still hard to predict how much the revetment type influences the final seaweed community composition at the climax state. The climax community of the seaweed population on dykes is dominated by brown seaweeds (Fucus vesiculosis, Fucus spiralis, Fucus serratus and Ascophyllum nodosum) and a variety of smaller red and green algae. Ascophyllum nodosum was a dominant species on the previous dyke at Sint-Annaland before it was renovated (personal observation).

Outlook

Ongoing research at HZ includes a simulation of a disturbance event where all seaweeds on a part of each section will be completely removed using a bush trimmer (Figure 1.). The aim of this research is to gain insight into the ability of the seaweed community to recolonize the substrate after e.g. winter storms. This research will be part of the educational program of the Bachelor study Watermanagement: Aquatic Ecotechnology at the Delta Academy.

Figure 1. The dyke at Sint-Annaland after treatment with a bush trimmer (February 2017). Photo: T. van Oijen.