Partial weed removal suits aquatic animals

Posted on September 22, 2010


Highly invasive waterplants  threaten biodiversity by outcompeting native species, and dense stands of exotic plants  reduce aesthetic values, impede recreational activities and block the intakes of hydroelectric systems.  While cost constraints mean that in many cases, the complete removal of invasive waterplants is out of the question, partial removal can still be worthwhile.  In theory, thinning of waterplant stands should lead to significant  improvements in invertebrate biomass  by increasing light penetration and primary production, and should also benefit fish by increasing the abundance and accessibility of their prey species.  These ideas were tested by cutting 2 x 3.5 m channels in dense stands of Lagarosiphon major (curly waterweed, an African species) inLake Dunstan,New Zealand.  Four months after the channels were cut the weed had largely grown back, covering 75% of the area, but light levels were still significantly higher in the treated zones compared to uncut control areas.  Invertebrate abundances were significantly greater in the treated areas, being three to four times higher in the case of grazing snails and crustaceans.  Fish abundances also increased, although not significantly so.

Reference: 

Bickel, T.O. & Closs, G.P.  2009.  Impact of partial removal of the invasive Lagarosiphon  major (Hydrocharitaceae) on invertebrates and fish.  River Research & Applications 25, 734–744. 

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