Native flora and fauna response to removal of the weed Hydrilla verticillata (L.f.) Royle in Lake Tutira

  • Published source details Hofstra D. & Clayton J. (2014) Native flora and fauna response to removal of the weed Hydrilla verticillata (L.f.) Royle in Lake Tutira. Hydrobiologia, 737, 297-308.


Actions: Introduce organisms to control problematic plants

A before-and-after study in 2008–2012 in a lake invaded by hydrilla Hydrilla verticillata in New Zealand (Hoftra & Clayton 2014) found that introducing grass carp Ctenopharyngodon idella affected the abundance of individual macrophyte species, but had no clear, long-term effect on overall macrophyte richness. Unless specified, statistical significance was not assessed. In the year before introducing carp, the lake was dominated by hydrilla (present at 15 of 15 survey sites). There were 15 aquatic macrophyte species present (plus two emergent). Around six months after introducing carp, the lake was still dominated by hydrilla (present at 15 of 15 sites) and contained only 11 aquatic macrophyte species (plus two emergent). Around 1.5–3.5 years after introducing carp, hydrilla was significantly less common (present at ≤6 of 15 sites). There were now 13–16 aquatic macrophte species (plus 1–3 emergent). The frequency of 11 native macrophyte species changed significantly over time. For example, in deeper water, watermilfoil Myriophyllum trichophyllum and stoneworts Chara spp. were more common after carp introduction than before (see original paper for data). Methods: Grass carp were introduced to Lake Tutira in December 2008 (100 carp/vegetated ha). Macrophytes were surveyed by a SCUBA diver at 15 sites around the lake, in autumn before (2008) and after (2009–2012) carp introduction.

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