Onderwerp: Perenbomen op/in het wad.

Volgens de info van RWS liggen er iets van boei(tjes) bij, maar de posities die ze daar voor geven vind ik zelf nogal flink er naast.

Diepte heb ik geen idee van. Toen ik daar in de buurt was niets boven water zien uitsteken

Volgensmij trek je de verkeerde conclusies. Als we voor het gemak even schatten dat die dingen 2m hoog zijn.[En die dingen liggen is dit vakje,
Dan zouden ze met LW bovenwater kunnen komen. De dikkere dieptelijnen zijn van resp. 1 en 2m diep!

This is also the case in the Dutch Wadden Sea, where natural hard substrates have gradually disappeared due to burial by sand and/or active removal by humans. In addition, driftwood that was historically imported from rivers has been nullified by upstream logging and coastal damming of estuaries.

Placement of tree-reef blocks
In April 2022, eight tree-reef units per trip were loaded onto the deck of a cockle fishing ship. These were deployed at the study sites in a square pattern of approximately 25 m2 (Figure 1B). For navigational safety, four large yellow buoys of 1.12 m were deployed 25 m out from each corner of the reef square: these were attached to 125 kg concrete weights of approximately 80 cm diameter and 30 cm height, secured by eight meters of 20 mm chain. Control plots were also marked by these buoys, though only two buoys were used since there are no hazards to navigation in control plots.

Figure 1 (A) Location of the tree-reefs (marked by triangles) in the Dutch part of the Wadden Sea. The inset provides a zoom in on the study area, showing that the tree-reef blocks (i.e., experimental plots marked by triangles) are located towards the ends of four subtidal gullies, where the morphology is relatively stable. ( Within each tree-reef block, we placed eight tree-reef units with five meter distance in between. (C) Each tree-reef unit consisted of six short-stemmed fruit trees, bolted together to form a pyramid shape. That is, three trees (upright legs) had a concrete weight at their base, and were bolted to three other trees (crossbeams) to create a self-reinforcing series of triangles that comprise the overall pyramid. (D) Picture of the barrel-fyke style net, referred to as traps, used to catch fish both nearby and away from the tree-reef.

Within six months, the tree-reefs were colonized by sessile hard substrate associated species, with a clear vertical zonation of the settled species. Macroalgae and barnacles were more abundant on the lower parts of the reef, while bryozoans were more dominant on the upper branches. In addition, six fish species were observed on the reefs, while only two species were caught on sandy control sites. Moreover, the abundance of fish on the reefs was five times higher. Individuals of the most commonly caught species, the five-bearded rockling Ciliata mustela, were also larger on the reef. These patterns also hold true for common prawn, Palaemon serratus, which were also larger and ten times more numerous on the reefs. Present findings indicate that the reintroduction of tree-reefs as biodegradable, structurally complex hard substrates can increase local marine biodiversity in soft-sediment systems within relatively short time scales.

het is 0,1 cm.