Science Centres: Aquatic Biodiversity and Biosecurity

Didymo continues to make headlines as it spreads through waterways in the South Island, with the latest confirmed incursion in the Ahuriri River, Canterbury.

Biosecurity New Zealand has commissioned NIWA to identify and trial biocides that could control or eradicate didymo without causing unacceptable environmental impacts. This will be a three-step process, involving product screening, product testing, and full-scale river control/eradication trials.

We have set up a facility for the screening and testing trials at Monowai Power Station on the banks of the lower Wairau River, Southland. We are currently screening 10 prospective biocides, testing their toxicity to didymo in small-scale controlled experiments. The biocides are ‘phytotoxins’, chemicals that will kill didymo cells directly.

At least two of the most promising biocides will undergo further testing in a large-scale trial in stream-side channels, where didymo will be incubated for up to two months. This trial will determine the effects of the biocides on didymo and also on non-target species, such as insects and fish.