Temporal variability of benthic invertebrate communities at reference sites in eastern Newfoundland and its significance in long-term ecological monitoring

Abstract

The reference-condition approach evaluates the ecological impact at a site of interest through comparisons to unimpacted sites of otherwise similar conditions. Reference conditions should ideally represent natural spatial and temporal variation of unimpacted systems, including infrequent disturbance events. This study examined the year-to-year variability of unimpacted benthic macroinvertebrate communities in the Terra Nova National Park, Newfoundland and Labrador, Canada. Sites were sampled annually in October from 2006 to 2011, a time series that included a 100 year flood event associated with Hurricane Igor. Invertebrate collections from a nearby urbanized area were compared to the natural temporal and spatial range of reference sites to determine the adequacy of this approach. Significant year-to-year changes in macroinvertebrate community composition were observed among unimpacted sites, particularly samples collected in the year of Hurricane Igor. These samples were characterized by a lower abundance, but had only minor differences in taxonomic richness. One year later, the benthic community composition showed signs of returning to pre-hurricane conditions. Despite significant temporal change, the variation associated with unimpacted communities was relatively small compared to differences observed at a site from a nearby urban area. These results suggest that reference conditions are clearly dynamic and need to be accounted for. However, at least in the case of invertebrate communities, the magnitude of change associated with anthropogenic impact can greatly exceed that associated with natural temporal variation.