Bfn Data analysis ecoblock revetments: verschil tussen versies

Huidige versie van 24 okt 2017 om 15:15

Example of a picture composite of a dyke section (left) and GIS-analysis of the same section where each color is a different species group/bare area (right). light green= gutweed; light brown=Fucus; dark brown=ectocarpales. Photos: E. Paree.

In April 2016, ten months after placement, the standard hydroblocks (Figure 1a.) were largely covered with Fucus on most parts of the full vertical range. Gutweed was still present higher on the dyke, above +0,50 mNAP. Here, also part of the surface is still bare. Ectocarpales are mostly present below NAP which is the case on all revetment types. The hydroblocks with an ecotop layer (Figure 1b.) were covered for a large part with gutweed in the middle and top part of the vertical range. Fucus cover seemed to increase when the gutweed decreases and vice versa. The lowest parts of the section were partly bare (up to 50%). The hydroblocks with a BfN-structure were nearly completely covered with Fucus over the entire vertical range (Figure 1c.). Gutweed was only present at the top and bottom of the section, covering a few percent of the block surface. The standard and porous Hillblocks (Figure 1d,e.) are also mostly covered with Fucus but below NAP its percentage cover was markedly lower than on the BfN hydroblocks. Gutweed was present at the top of the sections but in low percentage cover. The highest percentage of Ectocarpales (up to 50% in low intertidal) was observed on the Hillblocks. In September 2016, all revetment types were almost entirely covered with Fucus over the whole vertical range. The exceptions were the sections with hydroblocks with ecotop. On this revetment type gutweed contributed up to 20% to the seaweed cover at lowest part of the section.

Figure 1. Vertical kite graphs of the distribution of the seaweed species groups on the different revetment types. a: standard hydroblocks; b: hydroblocks with an ecotop layer; c: hydroblocks with a BfN-structure; d: standard Hillblocks; e: porous Hillblocks

Brown seaweed biomass

In October 2016 (t=16 months) the total biomass of all Fucus species was highest on the sections with porous Eco-Hillblocks followed by the BfN-hydroblocks and the standard Hillblocks (Figure 2.). The biomass of Fucus vesiculosus was highest on the BfN-hydroblocks and lowest on the hydroblocks with ecotop. On the hydroblocks with ecotop and on both Hillblock types Fucus spiralis was most abundant. The differences in biomass on the different BfN-types were minor.

Figure 2. The average biomass at t=16 months for the different Fucus species integrated over the full height range of the experimental dyke (-0,60 - +0,92 mNAP) on the different block types.

Fauna

After one year all revetments types were colonized by a variety of invertebrates The species (groups) most often observed were springtails (Anurida maritima), the common crab (Carcinus maenas), barnacles (cirripedia), amphipods and isopods. Periwinkles were encountered incidentally. There were obvious differences in the abundance of main fauna species groups on the different revetment types. Relatively high abundances of amphipods were found on the BfN-hydroblocks and on both types of Hillblocks, while abundances were low on the hydroblocks with ecotop. The abundance data on the common crab are not reliable since a larger surface would need to be sampled to get an accurate estimate.