NIWA Media Release 3 August 2011
NIWA fights against one of New Zealand’s biggest biosecurity invasions
Exotic aquatic plants, introduced to New Zealand for the aquarium and ornamental pond trade, are silently invading our
waterways, but new research by NIWA scientists is helping to lower this risk by finding native alternatives for the
Over 70 freshwater invasive aquatic plants have been introduced into New Zealand, with devastating consequences for our
native aquatic plants and other wildlife. Most New Zealand lakes, rivers, streams, and wetlands are now affected by at
least one species of introduced aquatic pest plants. Aquatic weeds cause serious problems for electricity generation by
clogging up hydro dams, impede irrigation and flood control schemes, damage indigenous freshwater ecosystems, and make
recreational activities, such as swimming and boating, difficult.
But working closely with the Federation of New Zealand Aquatic Societies (FNZAS) and MAF Biosecurity New Zealand
(MAFBNZ), NIWA is helping to stamp out the worst plant invaders.
“We estimate that 75 percent of aquatic weeds were introduced to New Zealand illegally through the aquarium and
ornamental pond trade, with a lot of the buying and selling going on over the internet,” says plant ecologist Paul
Champion. “These plants, and the organisms that hitch-hike on them, can have serious consequences for New Zealand, both
environmentally and economically.”
One of the best ways to stop further illegal imports of aquatic plants is to provide alternatives in New Zealand. NIWA
is working with aquarium owners to find the best native aquatic plants suitable for growing in warm water aquaria.
Following cultivation trials at NIWA, a variety of native aquatic plants were sent to aquarium enthusiasts to test
“The feedback we have received has been really positive,” says NIWA plant ecologist Kerry Bodmin. “Aquarium hobbyists
look for special leaf forms and shapes to enhance the look of their aquaria. Until now, they’ve had trouble finding
enough variety in the aquarium plants available in New Zealand. What we are showing them is that native aquatic plants
can be just as appealing as exotic plants, but not a risk to our national biosecurity.”
So far, 17 species of aquatic plants have been successfully cultivated as native alternatives for aquaria. The most
popular with the aquarium enthusiasts were Limosella lineata, a native turf plant, and Myriophyllum robustum, a
threatened native milfoil.
“Some good progress has been made popularising native outdoor pond plants, but native aquarium plants in New Zealand are
almost non-existent. Aquarium owners we spoke to said they’d happily buy the range of new native species NIWA provided
for evaluation, if they were available, so there’s a potential new market there.”
NIWA has also developed a model to evaluate the potential weed risk of aquatic plants. In the experiments, potential
weeds were grown in competition with known weeds and native plants, under different temperature, flow and water depth
conditions, to see how robustly they adapt to New Zealand conditions.
“Understanding the potential for different exotic plants to establish here has helped authorities prioritise which
aquatic plants to manage and control. As a result, 35 aquatic plants are now banned from importation and sale. That’s
huge help to New Zealand’s freshwater biosecurity,” Mr Champion says.
NIWA also helps MAFBNZ identify pest species brought into the country illegally. In 2005, NIWA identified 11 imported
plant species in a suspicious parcel intercepted by MAFBNZ, at the Auckland International Mail Centre. The importer was
selling the plants on Trade Me for aquariums and was sentenced to nine months’ imprisonment and a $25 000 fine– the
first prosecution for illegally imported aquatic plants in New Zealand.