Numerical, growth and secondary production responses of the benthic macroinvertebrate community to whole-lake enrichment in insular Newfoundland

Abstract

A whole-lake enrichment (N + P) experiment was conducted over a three-year period to evaluate the feasibility of boosting benthic productivity in insular Newfoundland lakes. Response of the benthic community to enrichment was monitored by a combination of biomonitoring (artificial substrate) and quantitative dredge sampling in both the enriched lake and two control lakes. -- Observations of benthic abundance through biomonitoring approaches revealed a continuum of positive numerical responses to enrichment. Responses were most rapid in short-lived herbivores such as chironomids, gastropods and sphaeriid clams while longer-lived detritivores (mayflies, amphipods) and predators (flatworms, leeches and dragonflies) demonstrated a slower, more modest numerical response. The benthic macroinvertebrate communities of the study lakes were composed of cosmopolitan species from the North American fauna in relatively low densities. Benthic biomass was dominated by gastropoda and the odonate Cordulia. Secondary production estimates were relatively low when compared to mainland systems. Short-lived herbivores (Amnicola, Phryganea) were observed to have increased secondary production in the enriched pond. Secondary production estimates were similar in the three study ponds for the other macroinvertebrate taxa. Some of these taxa were observed to have increased growth (Cordulia) and/or recruitment (Enallagma) late in the study. This pattern indicates that benthic macroinvertebrate community production was still increasing in the enriched pond.