Overview

Brief Summary

Taxonomy

Hydrodictyon reticulatum or water net cells aggregate to form colonies or mats.colonies or mats are
  • a single-layered membrane or sac-like network of several thousand cells
  • free-floating or secondarily attached
  • reaching over 50cm long
  • meshes clearly visible in large colonies
Cells are
  • cylindrical to oblong-oval, up to 15mm long
  • 2-4 adjacent cells connected by their edges and forming 5-6-sided meshes
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Introduction

Hydrodictyon reticulatum, a very invasive nuisance alga, is commonly known as ‘water-net’ reflecting the net-like structure of its sack or membrane-like colonies.Over the past 20 years it has become more common and widely distributed in ponds, lakes and rivers in the British Isles.Water net is a serious nuisance because it
  • clogs waterways and irrigation ditches,
  • taints potable water,
  • causes economic losses to trout fisheries,
  • smothers aquatic plants and fauna
  • adversely impacts boating, fishing, swimming and tourism
The rapid spread of the water net is believed to be a response to elevated and extended summer water temperatures and low river flows caused by climate change.
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Comprehensive Description

Biology

Reproduction
Cell contents cleave to produce unicellular, biflagellate zoospores or gametes. Unlike the zoospores the gametes are not released but lose their flagella and produce miniature colonies within the mother cell wall.The similar sized gametes fuse to form a zygote and these become thick-walled and angular. After a rest period each produces 2-5 zoospores each of which becomes an enlarged polygonal cell whose contents divide into flagellated cells which produce a new miniature colony.The miniature nets are released by gelatinisation of the cell wall.
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Distribution

Hydrodictyon reticulatum, water net, is an invasive species and is considered rare. However erratically water net appears it has been found across the globe.Although considered rare water net is frequently recorded in rice paddy fields in Asia. In late 1980s to early 1990s water net had a significant economic and recreational impact in the in the North Island of New Zealand where it appeared for the first time.Hydrodictyon reticulatum has been found in England for many years but is now spreading north and west. Reports of water net in Dumfries, Scotland and Cork in the Irish Republic have been recieved recently.

Habitat
Free-floating mats of often accumulate in vast quantity in sheltered bays along the downwind shores of ponds and lakes. These mats frequently blanket the surface and are capable of undergoing sudden changes in buoyancy and therefore disappear only to quickly reappear especially during calmer periods.

Water net frequently forms extensive surface and subsurface mats in ponds and lakes and in the marginal shallows of rivers during low flow conditions in the summer months.Conspicuous seasonal blanketing growths in:
  • Ponds
  • Reservoirs
  • Rivers
  • Streams
  • Ditches
  • Drainage channels
  • Wetlands
  • Patches of damp ground
Water net is often growing attached to the remnants of the filamentous green alga Cladophora.The rapid spread of water net is attributed to agents such as
  • wind
  • water movement
  • wildfowl
  • insects
  • livestock
  • humans
Water net mats generally disappear in September in such lakes and from rivers during the first floods of the autumn.
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Ecology

General Ecology

Ecology

The water net has negative and positive impacts on freshwater systems on the biota in lake systems.

Negative impacts
The water net is a serious nuisance alga because it clogs waterways and irrigation ditches, taints potable water, causes economic losses to trout fisheries, smothers aquatic plants and fauna and has an adverse impact upon boating, fishing, swimming and tourism.Shallow water mats
  • smoother beds of aquatic macrophytes causing their collapse and decay.
Extensive surface floating mats
  • reduce the aesthetic appeal of waters
  • interfere with recreational activities by
    • blocking marinas
    • hampering intakes of boat engines
    • swimming and fishing
On beaches water net accumulates in large drifts decaying and causing localized anoxic conditions.

Positive impacts
Some studies have demonstrated water net having a beneficial impact on invertebrates.

Climate change response
The rapid spread of the water net in the British Isles is believed to be a climate change response relating to elevated and extended summer water temperatures and low river flows.The sudden appearance of small (>2cm long), cylindrical colonies in May and June on the surface of a lake near Helston in Cornwall (UK) was associated with the water reaching 15°C. Such colonies increased in size several thousand fold within a few days and gave rise to entangled, cylindrical-shaped colonies blanketing the surface.
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Hydrodictyon reticulatum

The following is a representative barcode sequence, the centroid of all available sequences for this species.


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Statistics of barcoding coverage: Hydrodictyon reticulatum

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 7
Specimens with Barcodes: 7
Species With Barcodes: 1
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