Environmental effects on biofilm bacterial communities: a comparison of natural and anthropogenic factors in New Zealand streams

Summary We investigated the resident bacterial communities within the biofilm of 252 streams in N ew Z ealand with the aim of assessing the community variation associated with natural and anthropogenic‐influenced environmental characteristics. This work is part of a larger project investigating the use of bacterial communities as biological indicators, and here we assess how predictable the variation in bacterial community is in response to environmental influences. Samples of epilithic biofilm were collected in the A ustral S ummer of 2010, and bacterial communities were characterised using the DNA ‐fingerprinting technique automated ribosomal intergenic spacer analysis ( ARISA ). Multivariate analysis of the ARISA data revealed that geographical location (region) was a better predictor of bacterial community structure than land use. Our finding that taxon richness varied with geographical location, decreasing along a north to south (increasing latitude) gradient, and that land use had no significant effect on taxon richness suggests that bacterial communities have great potential to act as biological indicators of stream health. In particular, the maintenance of taxon richness at impacted sites is a key advantage since the local extinction of many traditional indicator organisms, such as fish or macroinvertebrates, often precludes their further use. Our conceptual model of bacterial community structure proposes that stream biofilm communities are comprised of four broad groups of bacteria: ubiquitous bacteria (found at all sites), region‐specific bacteria (those representative of geographical areas), natural‐state bacteria (those associated with unmodified systems) and impact‐related bacteria (those associated with human activities). The proportion of these four groups at a particular sample site would provide the basis of a novel bacterial community index of stream health.