Science Centres: Aquatic Biodiversity and Biosecurity

NIWA’s Rohan Wells with a hornwort find.

One of the worst water weeds in New Zealand, hornwort represents a major threat to the ecology and biodiversity of South Island lakes and rivers if it spreads. Hornwort can grow much deeper than other invasive species, displacing native vegetation to at least 16 m. The weed is a multimillion dollar cost to hydro-electric generators in the North Island, as well as impacting on irrigation and flood control schemes, with similar problems expected in the South Island if it escapes.

Biosecurity New Zealand asked NIWA to carry out a hornwort delimitation survey at Centennial Park Lake in Timaru, after DoC discovered the weed there in February. The weed was well established in the lake and some fragments were present immediately downstream, but upper and lower reaches of this stream system appeared to be clear.

With NIWA’s assistance, hornwort had been successfully eliminated from the few previously known South Island sites around Nelson. Biosecurity New Zealand is awaiting results of control measures at the Timaru site.