Salmon of the Prairie? Tracking the Fate of Common Carp Carcasses Following a Natural Disturbance

Pacific salmon Oncorhynchus spp. transport marine-derived nutrients from oceans into low productivity freshwater streams and substantially contribute towards ecosystem productivity through carcass decomposition.  Common carp Cyprinus carpio is a highly abundant invasive species throughout the Midwest that thrive in shallow eutrophic lake ecosystems where periodic anoxic conditions occur, also potentially providing an important nutrient subsidy through carcass decomposition.  However, the importance of nutrient subsidies of fish carrion in eutrophic-hypereutrophic ecosystems is unknown.  We evaluated nutrient availability, lake productivity, and invertebrate production in lakes from April through September following complete, partial, or no winterkill during the winter of 2007-2008.  Lakes with complete winterkill had an estimated 264 kg/ha of common carp carrion and released 104 g/ha total phosphorus and 585 g/ha total Kjeldahl nitrogen whereas lakes with partial kills had 23 kg/ha of common carp carrion and released 1,187 g/ha total phosphorus and 6,648 g/ha total Kjeldahl nitrogen.  Lakes with winterkill had higher nutrient concentrations, pH, turbidity, chlorophyll a, and zooplankton and benthic invertebrate abundance and less periphyton biomass compared to control lakes and effects were typically greater for complete than partial winterkill lakes.  Differences in nutrient availability and productivity among systems were detected shortly after ice-out and persisted throughout the summer.  Our results suggest that nutrients released during fish decomposition following stochastic disturbances can be an important nutrient subsidy in eutrophic lakes, further enriching lake productivity.