Community–habitat relationships in coastal streams in Big Sur, California, USA: travertine influences macroinvertebrate abundance and community structure

Travertine deposition occurs in streams worldwide but its effects on stream communities are poorly understood. I sampled benthic macroinvertebrates, periphyton, and reach-scale environmental variables in coastal streams in Big Sur, central California, USA, to determine the specific effects of travertine that occurred at some sites as well as to provide a broader assessment of community–habitat relationships. Total density and biomass of macroinvertebrates varied 6- and 9-fold across sites, respectively, and chlorophyll a concentrations varied 10-fold, but invertebrate and periphyton abundances were not correlated. Baetis tricaudatus (Ephemeroptera), Simuliidae (Diptera), and Chironomidae (Diptera) dominated macroinvertebrate communities across all sites, although differences in the relative abundances of these and other taxa produced moderate variation in community structure among sites (Bray-Curtis similarity coefficients of 47–84). Variation in community structure was related to a number of habitat features, notably travertine but also including variables reflecting channel morphology, flow, substrate size, and riparian tree type. Median density and biomass of macroinvertebrates were more than twice as high at sites without travertine than sites with travertine. Taxa richness also was higher at sites without travertine, and community structure differed moderately between sites with and without travertine, although there were no particular assemblages associated with either group. Non-metric multidimensional scaling (MDS) and cluster analysis of similarities in community structure appeared to separate sites with either travertine or high fines from sites without those conditions. These results demonstrate that travertine can have strong effects on stream communities, and additional studies are needed to identify the full range of effects on ecosystems and to evaluate the potential consequences of travertine for conservation efforts such as biomonitoring programs and threatened species management.