Genetic diversity is an important component of biodiversity. Recent NIWA research shows how contaminated stormwater can reduce the genetic diversity of one model freshwater species.

Contaminated stormwater running into urban streams can cause all sorts of problems for natural ecosystems. The most direct of these, which are well understood, include toxic effects and subsequent loss of sensitive species and selection of tolerant species, and disruption to natural food webs.

We know much less about how contaminated stormwater affects the genetic diversity of aquatic life and whether or not those changes affect future generations. NIWA scientists are working on ways to detect the effects of chronic, low-level stormwater contamination on multiple generations of aquatic species. While changes in genetic diversity are natural over evolutionary time scales, contaminants are known to speed up this process, leading to micro-evolution within just a few generations.

Freshwater clams: a good model species

We are using the native freshwater pea clam (Sphaerium novaezelandiae) as our 'model' species. It is an ideal model as its feeding and movement activities mean it is exposed to both sediment and water column contamination. It also has a relatively rapid life cycle, starting at around three months of age.

We ran experiments both in the field (five different streams in the Auckland area) and in the lab. In the lab we exposed the clams to contaminants for between 4 days (representing an 'acute' poisoning incident) to 38 days - a chronic period of toxicity.

Things we looked at included:

  • the effects of different levels of contaminants over short and long time periods on both adult and juvenile populations, especially on physiological and reproductive measures
  • changes in genetic structure between adults and juvenile populations, which helps us understand effects across generations. 

Key findings

So far key findings include:

  • stormwater contaminants can negatively affect both the reproductive ability and the genetic diversity of freshwater clams
  • this effect can be observed within a single generation
  • animals already exposed to contaminants are more vulnerable to additional stressors.

What next?

Populations with low levels of genetic diversity are vulnerable because they lose the ability to adapt, especially to extreme events. If we can measure the potential loss of genetic diversity associated with stormwater contaminants, we will be better able to contribute to ecological risk assessments associated with, for example, new development in urban areas.

Contact: Dr Ngaire Phillips