De Blauwe, H.

Open Marine Archive

  
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DIVERSITY AND LONG-TERM CHANGES IN THE BRYOZOAN FAUNA OF 
THE HINDER BANKS, BELGIUM 
De Blauwe Hans  
Afdeling Malacologie, Departement Invertebraten, Koninklijk Belgisch Instituut voor 
Natuurwetenschappen, Vautierstraat 20, 1000 Brussel, Belgium 
E-mail: deblauwehans@hotmail.com  
The Hinder banks rise about 25m above the seafloor and are about 20km long. Gravel fields are 
located in the gullies between the sand banks. The sand banks are characterized by large 
transversal sand waves. In a transitional zone, patches of gravels are present between large sand 
waves. The gravel field along the south-eastern flank of the Westhinder bank once hosted large flat 
oyster banks, which were destroyed by oyster dredgers in 1873. Nevertheless the samples of 
Gustave Gilson taken between 1900 and 1910 still reveal a very rich biodiversity on the Hinder 
Banks. Due to increased trawling, Gilson recommended in 1921 to protect gravel habitats. After the 
First World War, direct impacts to offshore gravels increased subsequently to the introduction 
motorized bottom trawling. After the collapse of herring in 1960, beam trawling was used to catch 
flatfishes with increasingly powerful ships. Continuous disturbance of the bottom has a devastating 
impact on erect growing fauna. Erect growing bryozoans like Flustra foliacea, Electra pilosa, 
Alcyonidium sp., Bugula flabellata and Vesicularia spinosa used to be abundant in Gilson’s time, 
nowadays erect colonies are rare. Only sheltered areas, where the beam trawl hops over the hill and 
can not reach the gravel zone, host more and larger specimens. Encrusting bryozoans e.g. 
Schizomavella teresae, Membranipora tenuis, Conopeum reticulum, Aspidelectra melolontha and 
Electra pilosa are now dominant on gravel. In 2005 the Hinder Banks were re-sampled with a 2m 
beam trawl (Houziaux et al., 2008). Up to 21 bryozoan species were found on gravel locations, 
covering large parts of the substratum. Surprisingly, the greatest diversity of bryozoans occurs on 
empty shells on sandbanks with up to 71 species per location. This study revealed 31 species new 
for the Belgian fauna. A great amount of species that are typically reproducing at small colony size 
as an adaptation to short survival on small unstable substrata, are added to the Belgian list. 
Escharella gilsoni and Escharoides bishopi described from the Kwintenbank (De Blauwe, 2006) are 
found again and probably some other species new to science are discovered. The campaign shows 
that some species well known from the English Channel are protruding in the southern bight of the 
North Sea.  The presence of Distansescharella seguenzai, Puellina nana and others show some 
resemblances with the fauna in the Rias in northern Spain. Thousands of shells in the Gilson 
collection still have to be screened to determine long-term changes in the bryozoan fauna on shell 
debris. 
 
References 
De Blauwe H. 2006. Bryozoa on shells from the Kwintenbank, Southern Bight of the North Sea 
(Belgium). Bulletin van het Koninklijk Belgisch Instituut voor Natuurwetenschappen. Biologie 
76:225-138. 
Houziaux J.S., F. Kerckhof, K. Degrendele, M. Roche and A. Norro. 2008. The Hinder banks; yet an 
important area for the Belgian marine biodiversity? Belgian Science Policy. Brussels, Belgium. 
248p. 


Diversity and long-term changes in the bryozoan fauna of the Hinder banks, Belgium

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