New guides to stream health

Posted on January 5, 2013

Because macroinvertebrate species vary widely in terms of pollution sensitivity, they’re  often used as rapid-assessment indicators of stream condition.  However, almost no attention has been paid to the potential advantages of using other organisms, such as bacteria and ciliated protozoans, as alternative guides to ecological structure and function.  A group of New Zealand researchers has compared the structure of macroinvertebrate, bacterial and ciliate communities in 18 freshwater streams in developed and undeveloped areas in the Auckland region.  They collected macroinvertebrates with a net after disturbing the substrate, and obtained genetic fingerprints of bacterial and ciliate communities from surface biofilms growing on rocks at each site.  The composition of all three types of aquatic communities varied with stream temperature and the concentrations of lead in the biofilms.   The richness of macroinvertebrate and ciliate, but not bacterial, communities was significantly lower at urban and rural sites than  at undeveloped forest sites.  Ciliate community structure varied with the degree of development, while bacterial community structure varied with the type of land use (rural or urban).  In contrast, macroinvertebrate  communities didn’t vary with either the extent or the type of land development.  These findings suggest that the three types of communities respond somewhat differently to catchment conditions, and that stream condition indicators based on bacteria and ciliates can be usefully employed alongside macroinvertebrate-based measures.   Advantages of the use of microbes include their ubiquity, their quick response to environmental change, the ease of microbial sampling, and the rapidity of genetic fingerprinting techniques.

Reference:  Lear, G., Dopheide, A., Ancion, P. & Lewis, G.D.  2011.  A comparison of bacterial, ciliate and macroinvertebrate indicators of stream ecological health.  Aquatic Ecology 45, 517–527.