_polymorpha_


h1. General
{section}{column:width=80%}
|| General characteristics || ||
| Common name  | Zebra mussel - _Dreissena polymorpha_ |
| Region | The Netherlands, Europe  |
| Watersystem | meren, rivieren |
| Nature parameter | molluscs |
| Factsheet made by | K.E. van de Wolfshaar, M. Haasnoot |{column}{column:width=20%}

| !Driehoeksmossel.jpg|thumbnail! |
| Photo: Ron Offermans Source:kennislink.nl|{column}{section}


h1. Descripton habitat

h3. Occurence
The zebra mussel lives in rivers, lakes, pools and canals and attaches itself to solid substrates. In winter, zebra mussels are consumed in large quantities by water birds, such as the Tufted Duck (Aythya _fuligula_), the Common Pochard (A. _Ferina_), the Greater Scaup (A. _marila_) en the Eurasian Coot (Fulica _atra_). It is a small freshwater mussel that lives in fresh, large stagnant waters in the lower river basin.


h3. Environmental boundary conditions
Fresh water, soil type, water depth and water temperature are important environmental conditions for the zebra mussel [#2], [#6]. 
They attach themselves to solid substrate such as rocks and shells. Zebra mussels are filter-feeding organisms, they remove algae from the water column. Water and soil that contain high silt concentrations hinder filter-feeding and can eventually cause suffocation. Lab experiments on mussel filtration of the zebra mussel under various inorganic silt concentrations showed that the filtration capacity of the zebra mussel decreases with increasing silt concentrations ([#11]). A silt concentration of more than 1g/l hinders the filtration. These concentrations result not only in slow silt filtration but also in slow green algae filtration ([#11]). This way, the mussels might not obtain enough food (as they are too busy with the removal of silt through pseudofaeces) which can lead to a lack of growth or even death. 
Most mussel colonies grow at various depths varying per area. There are reports of mussels at a depth of 50 metres ([#9]. Most concentrations can be found at a depth of 2-5 metres ([#2]). The zebra mussels do not occur in shallow areas, probably because of rapid temperature changes, mussel predator pressure or a high mortality rate in winter as a result of a long anaerobic period due to ice covering ([#8]). At larger depths, temperature and oxygen level are often limiting factors ([#10]). 
The water temperature influences the growth and reproduction of zebra mussels [#2]. The growth period is short and reproduction is minimal in cold water (<15˚C), Morton, 1969; Lewandowski, 1982; Strayer, 1991). Warm waters also have a negative effect on their reproduction (Walx, 1974). Mortality rate increases when temperature rises above 26-32˚C (Strayer, 1991). Noordhuis and Houwing (2003) suggest that relatively warm winters might have a negative effect. In Polish lakes, eggs and larval have been reported at water temperatures of 17-19 ˚C (Lewandowski, 1982) and in North American lakes at 13˚C (Hebert e.a., 1989). 


For the lake Ijssel, the yearly spring growth of the zebra mussels start in April and ends in September. Research by Reeders (1989) showed that filtration rate is optimal at a water temperature of 5-20˚C. Filtration rates abruptly decrease if the temperature drops below 5˚C. When temperature is above 20˚C, the rate gradually decreases. According to research (Morton, 1969), longitudinal growth only takes place at a water temperature above 11 ˚C and it comes to a complete stop when the water temperature is over 30˚C. The zebra mussel is extremely sensitive for rapid water temperature rises. Therefore, the thermal shock method is used to control zebra mussels in cooling water systems: at a temperature of 35˚C all new growth is dead within half an hour (Jenner en Mommen, 1985). The growth of zebra mussels in the Randmeren is limited by a number of factors, including rapid water temperature rise and large daily temperature fluctuations, which can occur in shallow and sheltered lakes in spring. These changes can completely disturb the reproduction of zebra mussels (Vanhemelrijk e.a., 1993).


h3. Control and growth opportunities
The occurrence of zebra mussels is mainly influenced by changes in salinity, water depth and water temperature. 


h1. Dose-effect relations
The dose-effect relations have been based on an extended study of TNO  ([#2]) and an expert meeting ([#3]).  For lakes and rivers, a distinction is made between water depth and flow velocity [#2]


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h4. Flowchart
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{flowchart}

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{flowchart}
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{flowchart}

\\
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"node3" [
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"node0":f1-> "node3" [style=italic,label="minimum"];

{flowchart}
\\



h4.