Rock snot is a tenacious beast
Science Centres: Aquatic Biodiversity and Biosecurity
Each didymo plant is microscopic, but they grow in extraordinary abundance. We have measured it at up to 10 times the national guidelines for acceptable algal biomass.
The invasive alga Didymosphenia geminata (didymo) has now been found in several significant fishing rivers in the South Island.
NIWA scientist Cathy Kilroy discovered didymo for the first time in New Zealand about a year ago. Since then, we have been working intensively behind the scenes providing research and scientific advice to Biosecurity New Zealand so that it can make well-informed decisions on containment and/or eradication measures.
Research we have conducted for Biosecurity New Zealand includes:
1. The effect of floods on didymo
We have discovered that didymo can withstand much bigger floods than typical nuisance algae found in New Zealand rivers, especially if the riverbed is stable. This means it will persist for much longer than current algal species when a bloom occurs.
2. Suitable conditions for didymo
Didymo will grow in a very broad range of river conditions. It is not too choosy about the depth of water or the speed of the river flow so it is unclear whether manipulating flow will be effective against didymo. We estimate that over 50% of New Zealand’s rivers contain suitable habitat for the establishment of didymo, with most of those rivers being in the South Island.
3. Didymo’s effect on the food chain
In areas where didymo has become established we see many more invertebrates. However, they tend to be smaller than in unaffected areas, and there are much higher proportions of invertebrates normally associated with polluted or low quality water. Such invertebrates are considered poor quality food for fish. However, the effects of didymo on fish have yet to be investigated.
NIWA also tested methods for cleaning items, such as kayaks, which have been exposed to affected waters. For more information: www.biosecurity.govt.nz/didymo