Posted by: lensweb | October 13, 2011

Azolla Invades Erewash Canal

Azolla on Erewash Canal

Azolla filiculoides covering Erewash Canal

Water fern (Azolla filiculoides) has completely covered areas of the Erewash Canal near Sandiacre. Reference was found to another photo taken by David Lally on 24th September, shows Azolla covering a stretch of the same canal in Long Eaton. Marion Bryce has also reported sightings of the fern in the River Erewash at Toton and the Trent at Beeston.

This non-native species can have serious impact on waterbodies as it;

  • Forms dense rafts and outcompetes native plant species. Also a danger to children, pets and livestock, which may attempt to walk on the apparently dry land.
  • Reduces light levels below the rafts which can cause die off of waterweeds and algae and reduce water oxygenation levels.
  • Deoxygenates water killing fish and other fauna.
  • Blocks water bodies and may lead to an increased risk of flooding.
The plant is a native of North America, and is probably the only species of floating fern found in Britain. The most characteristic feature of this plant is the red colouration taken on over the winter or when the plant is stressed, it is usually green during the summer months. It reproduces both vegetatively as the fronds grow and sexually by producing spores. Germinating spores can give rise to dense infestations of this plant and are the main method of overwintering. Spore production occurs as a result of stress when the plants start to form dense mats. The spores are released into the water so that controlling or harvesting the floating mats after this stage will not prevent re-infestation. The plant is free-floating often building up into thick layers where wind and currents collect it. Azolla’s nitrogen fixing properties have led to its use as a fertiliser, and a farmer in the Philippines is cultivating the fern as a livestock feed.
Azolla can grow in any depth of water but is not tolerant of waves or turbulence and can be flushed away in fast flowing waters. Due to spore formation, Azolla filiculoidesis is very difficult to eradicate, however, biological control by a weevil, effective against this plant in South Africa, has been observed on several occasions to be associated with Azolla in the UK. The weevil is called Stenopelmus rufinasus and is characterised by a yellow striped back. It is about 2 mm long.
A significantly smaller raft of the fern was also noticed by the author on Clifton Pond, Attenborough in October 2010.
Azolla filiculoides magnified image

Azolla filiculoides – magnified


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