Multivariate analyses of invertebrate community responses to a C12-15 AE-3S anionic surfactant in stream mesocosms

The ecological effects of a C(12-15)AE-3S linear alkylethoxysulfate anionic surfactant on aquatic organisms were studied in stream mesocosms. Analyses of the experimental data have yielded multiple population-level no-observed effect concentrations (NOECs) but did not provide a measure of community-level response to surfactant exposure. In the present study, the invertebrate data from the mesocosm study were further examined for community-level effects using multivariate techniques. Two multivariate statistical methods were selected as representative of recommended methods and used to analyze invertebrate abundance. One method was similarity analysis using the Bray-Curtis index, and the second method was the canonical ordination technique principal response curves recently developed for analysis of mesocosm data. Both sets of techniques detected statistically significant changes in invertebrate community structure following surfactant exposure. Ordinations constructed from Bray-Curtis similarity matrices provided clearer two-dimensional representations of these changes than ordinations from redundancy analysis. Re-displaying treatment and temporal effects on community structure on separate axes as response curves provided a clearer method for interpreting community response to surfactant exposure. Both approaches detected treatment effects in low and high abundance taxa. The highest rank abundance taxa in the pretreatment streams contributed very little to the differences observed between the control and treated streams. The same set of taxa was identified as the dominant drivers for structural differences between control and treated communities despite underlying mathematical differences in these two methods. Invertebrate community-level NOECs estimated from these different multivariate methods (2.5-5.0 mg/l) were comparable and these NOECs were similar to invertebrate population NOECs determined for this surfactant.