SECONDARY PRODUCTION OF CHIRONOMIDAE IN A LARGE EUTROPHIC LAKE

Abstract

To date the majority of food web research in lentic systems has focused on pelagic primary (phytoplankton) and secondary (zooplankton) production as the primary energy sources for higher trophic level production. Recently research has provided evidence that benthic secondary production of primary consumers can impact pelagic fish production and food web structure in lakes. I calculated secondary production of chironomids in Lake Winnebago Wisconsin where previous research has shown that lake sturgeon (Acipenser fulvescens) rely heavily on the benthos (chironomids) as a food source. I also calculated lake sturgeon annual production from literature-derived data using the instantaneous growth method in order to determine if there is sufficient chironomid production to support the current lake sturgeon population in Lake Winnebago. Benthic samples were collected with an Ekman dredge at four profundal sites on eleven dates from spring 2008 through spring 2009. Instantaneous growth rates for seven chironomid length-classes at five thermal regimes were measured in the laboratory. Mean annual production of Chironomidae using the instantaneous growth rate method was 7.59 g dry mass (DM) m-2 yr-1. The subfamily Chironominae accounted for 5.56 g DM m-2 yr-1 and Tanypodinae production was 2.04 g DM m-2 yr-1. Lake sturgeon annual production was estimated at 0.044 g dry mass (DM) m-2 yr-1. Mean annual density of Chironomidae was 2714 m-2 and mean biomass was 2.75 g DM m-2. In 2008-2009 there was sufficient chironomid secondary production to support the lake sturgeon population in Lake Winnebago. The annual production estimates for chironomids are higher than many other chironomid production rates from lakes in North America, presumably due the eutrophic conditions of Lake Winnebago.