Publication Date:
2024-01-12
Description:
The bivalves of the Noordzeekanaal (Mollusca: Bivalvia)\nIn recent years, the macrobenthos of the Noordzeekanaal area, west of Amsterdam, has been\nsurveyed intensively. The area consists of a main, brackish channel and a set of deep sea\nharbours. It was discovered that several bivalve species were present in large numbers. Many\nfindings came as a surprise.\nEspecially noteworthy is the presence of a (formerly unknown) sizeable population of lagoon\ncockle Cerastoderma glaucum. This species has only a sparce distribution in the Netherlands (and\nsurrounding countries). Also, the sand gaper Mya arenaria was found to be remarkably common\nin many places. The false dark mussel Mytilopsis leucophaeata was already known to be abundant\non stony substrate alongside the canal, but was found to be locally abundant on the channel\nbottom as well. The findings of the marine common basket shell Corbula gibba and\npeppershell Abra nitida were remarkable. Both species seem to have become more common\nsince the late 1990s in deep, man-made waters like channels and inland brackish harbours.\nSeveral other marine species were found in small numbers: cut trough shell Spisula subtruncata,\nrazor clam Ensis directus, American piddock Petricola pholadiformis, edible cockle Cerastoderma\nedule and Baltic tellin Macoma balthica. These have probably reached the area through the\nIJmuiden-sluices. Also, some fresh water species were found: zebra mussel Dreissena polymorpha,\npainter\xe2\x80\x99s mussel Unio pictorum as well as both Asian clams Corbicula fluminea and C. fluminalis.\nTowards the end of the 19th century the Noordzeekanaal was constructed. The former IJ was\nlargely reclaimed, reducing the habitat of the sand gaper and lagoon cockle to just a narrow\nchannel of 25 km long and several km wide, in total less than 10% of the original distribution\narea of these species. When the Zuiderzee was closed in 1932, the water of the Noordzeekanaal\nturned fresher. On top of this, the Second World War had the IJmuiden sluices closed, reducing\nthe inlet of seawater into the Noordzeekanaal. However, we assume that both the lagoon cockle\nand sand gaper have not disappeared from the Noordzeekanaal. A sufficient amount of brackish\nwater remained over the bottom of Noordzeekanaal, sufficient to sustain a small population of\nboth sand gaper and lagoon cockle. The stratification of the Noordzeekanaal-water has surely\nplayed a role in this, as the salt water was forced down (halocline). A completely fresh water\nsituation on the bottom was never reached. Thus, we suggest that the populations of sand gaper\nand lagoon cockle have survived as relics from the Zuiderzee-era.
Keywords:
tweekleppigen
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Nederland
;
verspreiding
Repository Name:
National Museum of Natural History, Netherlands
Type:
info:eu-repo/semantics/article
Format:
application/pdf
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