Populations and communities

Benthic ecology: lower Selwyn River

In the early 1970s Mike Winterbourn investigated the life histories of the stonefly Stenoperla prasina and its main prey the mayfly Deleatidium at Chamberlain’s Ford on the lower Selwyn River, Canterbury. In 2007 Mike decided to repeat the study with emphasis on the life histories and population dynamics of Deleatidium and a second mayfly Atalophlebioides cromwelli not seen there 30 years ago.
The field programme, which is based on monthly benthic sampling, has been running for two years and was modified to examine the effects of an extended period of low flow and a very large flood on the benthic community. Importantly, Mike's fortuitously timed field programme has meant that extensive pre- and post-disturbance data are available with which to assess effects on the benthos. Mike has also been able to evaluate the effect of these disturbances on the MCI and QMCI, indices used to evaluate river health.
Despite major changes in abundance of invertebrate species over time, disturbances had only small effects on the MCI (mean 104, coefficient of variation 6.1%; Fig. 1).

Figure 1. MCI and QMCI scores for the Selwyn River at Chamberlain’s Ford from March 2007 to December 2008

However, the QMCI was much more variable (mean 5.8, coefficient of variation 22%) and was strongly influenced by the relative abundances of the two numerically dominant taxa, Deleatidium (MCI score 8) and the caddisfly Pycnocentrodes (score 5). In the recovery period after the flood it fell dramatically as larval Orthocladiinae (score 2) and small Oligochaeta (score 1) dominated the fauna (Figure 1). In contrast, the MCI score was at its highest (121) in November when the QMCI was only 2.4.

People involved in this project

University of Canterbury
Mike Winterbourn