Invasive species not entirely bad

Posted on May 26, 2009

Dense stands of invasive plants can have serious negative impacts on aquatic ecosystems – for example, they can impede water exchange, reduce nighttime oxygen concentrations and change pH levels.  Nevertheless, depending on the growth form of the species concerned, they can still provide structurally suitable habitats for fish and their macroinvertebrate prey.  Thus their overall impact will depend on the balance between their negative and positive features.  Lagarosiphon major is an exotic macrophyte that commonly outcompetes and replaces native aquatic plants.  In Lake Dunstan, New Zealand, it forms a dense band around the entire lake perimeter and extends to a depth of about 6 m.  The biomass of a native fish species (the common bully, Gobiomorphus cotidianus) increases with the density of Lagarosiphon, and bully diets are dominated by invertebrates commonly associated with macrophytes.  Although removal of the weed isn’t feasible because it easily recolonises from upstream, it seems that Lagarosiphon can provide some ecosystem functions in disturbed habitats.

Reference: Bickel, T.O. & Closs, G.P. 2008.  Fish distribution and diet in relation to theinvasive macrophyte Lagarosiphon major in the littoral zone of Lake Dunstan, New Zealand.  Ecology of Freshwater Fish 17, 10–19.