Secondary production of Chironomidae in a large eutrophic lake: implications for lake sturgeon production

Most foodweb research in lentic systems has focused on pelagic primary (phytoplankton) and secondary (zooplankton) production as the primary energy sources for higher trophic-level production. Recent research has demonstrated that secondary production of benthic primary consumers can affect pelagic fish production and foodweb structure in lakes. We used the instantaneous growth method to calculate secondary production of chironomids in Lake Winnebago, Wisconsin (USA), where previous research has shown that lake sturgeon (Acipenser fulvescens) rely heavily on the benthos (chironomids) as a food source. We also used literature-derived data and the instantaneous growth method to calculate annual production of lake sturgeon to test whether chironomid production is sufficient to support the current lake sturgeon population in Lake Winnebago. We collected benthic samples with an Ekman grab at 4 profundal sites during ice-free conditions on 11 dates from spring 2008 through spring 2009. We measured instantaneous growth rates for 7 chironomid length classes at 5 thermal regimes in the laboratory. Mean annual density of Chironomidae was 2714 individuals/m(2), mean biomass was 2.75 g dry mass (DM)/m(2), and mean annual production of Chironomidae was 7.59 g DM m(-2) y(-1). Estimated annual production of lake sturgeon was 0.02 g DM m(-2) y(-1) in 2007. We concluded that in 2008-2009 chironomid secondary production was sufficient to support the lake sturgeon population in Lake Winnebago. The annual production rates for chironomids in Lake Winnebago are higher than rates in many other lakes in North America, presumably because of the eutrophic condition of Lake Winnebago.